5.4 Installing Plant Materials

Once the project site has been prepared (Section 5.2) and the plant materials have been obtained (Section 5.3) the vegetation can be installed on the project site. The following implementation guides cover the methods for installing seeds, cuttings, and plants. Section 5.4.1 discusses the different methods of seeding, how to formulate seed mixes, determining seeding rates, and ensuring quality. A specialized form of seeding, hydroseeding, is discussed in Section 5.4.3 outlines cutting installation techniques most commonly used in biotechnical engineering designs. Section 5.4.4 discusses techniques for planting bareroot and container plants. It also discusses seedlings, plant handling, storage, and quality control measures.

5.4.1 Seeding

Introduction

Seeding is the distribution of seeds for the purpose of establishing seedlings at a desired density and species composition. In addition to careful site preparations and seed treatment, optimal seeding operations should incorporate how seeds are uniformly distributed over an area; where seeds are placed vertically (that is, in, on, or under the soil surface); species composition in the seed mix; and when seeding takes place. These factors should be adapted to each revegetation unit to account for the unique climate, soils, and species requirements.

Seeding is often coupled with other operations, such as fertilization, soil amendment applications, and soil stabilization treatments. While accomplishing these objectives at the same time as seeding often makes practical sense from an economic and scheduling standpoint, it might not always be best for the short-term establishment of native vegetation. It is important to consider the effects of combining too many operations into the sowing operation. It may be necessary to plan some of these operations at different times. For example, fertilizing, which is often done during the seeding operation, might best meet objectives if applied separately from seeding (Section 5.2.1).This section describes the seven steps in developing a seeding plan: (1) identifying seeding areas, (2) determining seed application methods, (3) developing seed mixes, (4) determining sowing rates, (5) preparing seed mixes, (6) selecting sowing dates, and (7) applying seed and ensuring quality.

Identify Seeding Areas

It is important to visit the project site as soon as possible and specifically identify seeding areas on the ground. If road construction is a multi-year project, finished slopes should be assessed for seeding while the remaining construction continues. This may be the case if water quality permits are required given that they have specific timeframe requirements for slope stabilization (i.e., earthwork must be permanently stabilized with 14 days of completion). While most seeding areas will conform to the revegetation units developed during planning, sites often look different after construction. A field review should note where topsoil has been placed, the presence of surface rock, surface roughness, accessibility by equipment, microclimate, soil compaction, and other site factors. These factors will be used to develop seeding methods, sowing dates, seed mixes, and seeding rates for each of the seeding areas.

Seeding areas are located on a map and by road station. For each seeding area, acreage can be calculated using the methods described in Table 5-1. These calculations should consider the areas where seeding will actually occur. For example, seeds should not be applied in areas where herbicides will be used for maintenance. At the end of the field survey, the total acreage for each seeding area should summarized and used to develop seed mixes for each seeding area (Section 5.4.1, see Prepare Seed Mixes).

Determine Seeding Methods

A variety of methods for applying seeds are available to the designer. A challenge lies in matching these methods to the sites encountered in mountainous terrain. Typically, the site characteristics of each seeding area will dictate the type of seeding method used. For example, a road project might have three revegetation units: a steep, north-facing slope; an obliterated road; and a rocky south slope. Hydroseeding could be planned for the steep, north-facing slope where other equipment cannot reach. On the obliterated road, several ground-based seeding methods could be used, including mixing seeds into the soil or broadcasting on the surface and covering with a mulch. The south-facing slopes could be hand-seeded, then covered by a mulch to keep the seeds from drying out during germination or hydroseeded using a bonded fiber matrix mulch. Each project will most likely have site-specific seeding strategies to provide optimal conditions for seed germination.

Moreover, each plant species have unique seed covering requirements. While seeds of most species should be buried in the soil or covered by mulch to germinate, some species require partial exposure to light to germinate and should not be covered very deeply. A general rule for seed covering is to bury seeds at depths from twice (Munshower 1994) to three times (Monsen and Stevens 2004) the seed diameter. The deeper the seeds are covered, the less likely they will dry out during germination. The tradeoff, however, is that seedlings will have to expend more energy to emerge from deeply buried seeds. This can ultimately affect early seedling establishment.

The ideal seedbed, as defined in Monsen and Stevens (2004), is "one in which the seed is firmly enclosed within soil particles to provide hydraulic conductivity of moisture to the seed. Seeds should be placed deep enough to prevent rapid drying but shallow enough to allow natural emergence." Creating an ideal seed environment is an important practice, especially in nurseries, farms, or gardens where the objective is to create a uniform plant crop. All operations in these settings should be standardized and uniform (e.g., correct seed depth, optimum lighting, uniform irrigation, and uniform seed densities). While uniformity and standardization can be applied to wildland revegetation, an alternative strategy could be considered. This strategy starts from the premise that information about the specific germination and early seedling growth requirements of different native species at each seeding site is difficult to obtain. For this reason, a variety of environments, or "regeneration niches" (Grubb 1977), should be created where seeds might find the right conditions for germination (Figure 5-82). Further, a range of native species should be applied to fill these environments. With roadside revegetation, uniformity is not the objective. In fact, some randomness will most likely fit with the surrounding plant communities.

Vertical seed placement, where seeds are vertically distributed in soil or mulch layers, can be grouped into the following categories:

• Broadcast onto the surface
• Pressed into the soil surface
• Mixed under the soil surface
• Drilled under the soil surface
• Covered with long-fiber mulch
• Mixed into long-fiber mulch
• Covered with hydromulch
• Mixed into hydromulch

Vertical seed placement methods are discussed in the following sections in the context of how they affect germination and seedling establishment.

Seeds Sown on the Soil Surface—One of the most common forms of seeding is broadcast seeding, which is casting seeds on the surface of the soil with a rotary spreader or by hand. Broadcast seeding is almost always the least expensive form of seeding. Rotary spreaders can be attached to most types of vehicles, including all-terrain vehicles and pickups, and used where vehicle accessibility is adequate. Where slope gradient or accessibility limits mechanical seeding, the use of a hand-held broadcast seeder is a viable option. Because of this, although manual broadcast seeding might be considered a low-tech method, it still has an important place in revegetation.

Manual broadcast seeding offers the opportunity to spot-seed microsites at different seed rates and seed mixes. For example, two people could hand seed a steep cut slope requiring two different seed mixes—the lower portion of the slope sown with a grass and forb seed mix and the upper portion with a shrub and seed mix. In another instance, a fill slope composed of rocky outcrops interspersed among deep soils is composed of two distinct microsites that could be seeded separately with different seed mixes. With knowledge of the road objectives, several hand seeders can apply seeds across a project area that mimics the vegetative patterns of the landscape. Spot-seeding can also be a method of applying valuable seeds or "unique" species to strategic locations. For example, showy forbs that may have benefits to pollinators might be expensive to obtain or require a specific habitat can be spot-seeded in those locations.

The disadvantage of broadcast seeding is that seeds are not covered by soil or mulch (Figure 5-83). Because seeds need intimate contact with soil to germinate, broadcast seeding typically results in low establishment of seedlings. If greater quantities of seeds are sown; however, some seeds will find microsites with high humidity (between surface gravels or rock) or will be covered by soil particles that have been moved through erosion processes. An estimated 50 to 75 percent more seeds should be sown to compensate for the inability of seeds to germinate or the loss of seeds to rodents (Monsen and Stevens 2004). Survival factors should be adjusted downward when calculating sowing rates for seed mixes (Section 5.4.1, see Prepare Seed Mixes). Broadcast seeding on roughened surfaces can potentially increase germination rates, especially if seeds are sown in the fall. The probability that seeds will be covered by sloughing soil over time is increased (Stevens and Monsen 2004), so it is important that the soil surface be left as rough as possible where broadcast seeding will be used.

Seeds Pressed into the Soil Surface—Seed that is sown on the surface and pressed into the soil increases germination rates over broadcast sowing. Seeds are in firm, intimate contact with the soil, that increases available water to the seeds (Stevens and Van Epps 1984, Figure 5-84). Imprinting produces a variety of microsites that may benefit the germination of multiple species (Stevens and Monsen 2004). This type of seeding is accomplished with imprinting equipment (Section 5.2.2, see Roughen Soil Surfaces). In this operation, seeds are dropped from a seeder mounted in front of the imprinter and then pressed into the soil. Imprinting works well for small- to medium-sized seeds; seeds are in firm contact with the soil but not buried too deeply to affect seedling emergence. In some cases, imprinting small- and medium-sized seeds can result in germination as good as, or better than, drilling seed (Haferkamp and others 1985). Larger seeds should be covered by soil or mulch for adequate germination. Imprinting seeds cannot occur on steep slope gradients or slopes with high rock content. Sites that are too steep for tractor access are too steep for current imprinting equipment.

Seeds Mixed under the Soil Surface—Mixing seeds into the surface of the soil is one of the best ways to achieve optimum germination (Figure 5-85). Mixing is done in two stages: seeds are applied on the soil surface by either broadcast seeders or by using a seedbox and drop tubes, and then seeds are incorporated into the soil by dragging anchor chains, disk chains, cables, pipe harrows, or other implements behind a tractor or other all-terrain vehicles. Speciallized, equipment has been developed for wildland conditions that will apply and incorporate seed in one operation. The "ripper-seeder-harrow" (Figure 5-86) is a specialized seeder that simultaneously subsoils, broadcasts seeds, and mixes in one operation. Use of this equipment is limited to slope gradients of 1V:3H or less and non-rocky soil surfaces.

On steeper slopes, any method that scarifies the soil surface after seeds have been broadcast will mix the seeds into the surface (Figure 5-87). Using a hand rake to incorporate broadcast seeds into the surface works well and can be used in areas where expensive or valuable seeds have been applied. This type of seed placement requires that the seed depth be monitored to ensure that it is not buried too deeply. Seeds should not be mixed deeper than 1 inch.

These application methods allow seeds to be mixed evenly through the soil and not be concentrated in rows, as they are with drilling (see below). However, soil is left loose around the seeds, which decreases water-holding capacity and seed-soil contact. If seeds are sown in the fall and do not germinate until the following spring, natural packing of soil around the seeds will occur.

Seeds Drilled under the Soil Surface—Using a seed drill is another method for covering seeds with soil. Seeds are not actually drilled into the soil, as the name implies, but sown just under the surface in rows. Seed drills first open the surface of the soil with a disk or tine; drop seeds from a seedbox through tubes into open furrows; close the furrows with a disk; and finally pack the soil firmly around seeds with a press wheel. Cropland drills have been developed for the agricultural industry. However, this equipment has limited applicability on highly disturbed sites because rocky soils and uneven soil surfaces create difficulties in placing seeds at proper soil depths. Several drills have been developed for rangeland restoration that compensate for these limitations. The Rangeland and Truax® drills were specifically developed for seeding rocky, uneven surfaces and would work well on roadsides with shallow cross slopes. The Truax® drill was an improvement on the Rangeland drill and includes three seed boxes that can independently distribute seeds at different depths corresponding to the size and shape of the seeds (Stevens and Monsen 2004).

Seed drills concentrate seed into rows (Figure 5-88), creating a greater potential for competition between emerging seeds within rows than if seeds were broadcast. For example, a seed mix with an aggressive species will emerge and dominate the row of seeds at the expensive of less aggressive species. The three seedboxes on the Truax® seed drill can be used to compensate for this potential problem. The less aggressive species are placed in separate seedboxes and sown in separate rows. If more than one seedbox is used, separate sowing rates should be calculated for each box. Moreover, the three seed boxes can each accommodate a different type of seed such as very small or large seeds or fluffy seeds. The various seedboxes allow for these seeds to be sown separately into different rows to account for the required sowing rates. Typically, lower seed rates are used in drilling operations because the seeds are concentrated in rows and closer together. Fewer seeds are also used because of increased seedling establishment due to the improved seed-soil contact that results from using this equipment and technique. Where rodents are present, drilled seeds are more prone to being excavated by rodents that simply follow a row of seeds (Stevens and Monsen 2004).

Seeds Covered with Long-Fibered Mulch—Optimum seed germination is obtained under long-fibered mulch. The mulch provides a moisture barrier that protects seeds and keeps soil from drying (Figure 5-89). Soil moisture is maintained longer around seeds than if they were only covered by soil. This is a two-stage operation in which seeds are broadcast on the soil surface and then covered by mulch. The thickness at which the mulch is applied depends on the seed size and the type of mulch. Small seeds will require less cover than large seeds. The rate at which mulch can be applied varies by the characteristics of each type of mulch. Wood strands and straw, for example, can be applied at higher rates (thicker layers) than composts or chips because more light is able to penetrate these mulches, allowing seed germination and seedling establishment. Refer to Section 5.2.3 for further discussion of mulches.

Sowing seed mixes that contain a variety of seed sizes will require that the mulch not be uniformly applied. One strategy is to begin with a roughened seedbed, as shown in Figure 5-86. Because the surface is not even, mulch will settle in depressions and be thicker than on the ridges. Monitoring the application rates is important to ensure that seeds are covered with the proper mulch thickness. While covering seeds with long-fibered mulch is the most favorable method for optimum seed germination, it is also the most expensive. On slopes tackifier can be used to strengthen the cross linking of fibers and the mulch's bond with the soil.

Seeds Mixed into Long-Fibered Mulch—Seeding and mulching are often combined into one operation (Figure 5-90). Most mulch blowers have seed metering systems that distribute seeds with the mulch as it is being applied to the soil surface. Seeds in this operation are distributed within the mulch, as opposed to being placed between the soil surface and mulch layer. Although combining these applications in one operation is more efficient, seed germination and seedling emergence rates are typically lower than when seeds are broadcast on the surface and covered with mulch. When seed is mixed with the mulch, much of the seed will end up on the surface of the mulch and not in contact with the soil. Unless the mulch has a high water-holding capacity, moisture around the seeds will be limiting during germination and seedling emergence. It is important to know how much moisture a mulch can hold when deciding whether seeds will be mixed with the mulch or broadcast applied first then covered with mulch (Section 3.8.1, see Rainfall Interception) for determining moisture-holding capacities of mulches). Composts, for example, have high water-holding capacities, and seeds will typically germinate well in this material; ground or shredded wood mulch and wood strands have very little water-holding capacity and seed germination will be lower. Seed rates should increase relative to how much moisture the mulch is expected to hold. For low water-holding capacity mulches, seeds in the upper portions of the mulch will not germinate or will germinate poorly. Seed rates in this type of mulch should be increased by 25 to 50 percent.

Seeds Applied in Hydromulch—When seeds are applied through a hydroseeder (Section 5.4.2), they will lay on the soil surface surrounded by a covering of fine-textured wood fibers (Figure 5-91). Contractors sometimes apply seeds in hydromulch at less than the manufacturer's application rate and when this occurs seeds will be covered with less than 0.25 inch of mulch, with some seeds not covered. As rates approach 3,000 lb/ac, mulch thickness increases to over 0.25 inch, with most seeds being covered. Some products have a recommended application rate of 4,500 lb/ac. Hydromulch has a high water-holding capacity, maintaining thousands of times its dry weight in water. This can be beneficial to seeds during germination. However, unless very high rates of hydromulch are applied, many seeds in the slurry are not covered by the hydromulch. Some hydroseeding operations try to apply a thin mulch slurry with tracer dye and tackifier and with all the seeds first and then covering the seeds with hydromulch in a second pass. Critically, the total mulch thickness will be determined by the second pass. Hydroseeding is a common method of seeding for roadsides because large areas can be covered in a short time and it holds seed in place with the soil to germinate. Some damage to the seeds can occur through the pumps and agitators or by hitting the ground at very high speeds during application.

Hydroseeding is one of the most common methods of applying seeds to road construction disturbances. It is often the only way to place seeds on steep, rough terrain encountered in mountainous regions. Hydroseeding strategies that maximize good germination include increasing the amount of seeds, applying seeds in the first pass then covering with hydromulch in the second pass, and applying rates of mulch not less than manufacturer's recommendations. Fall hydroseeding also increases establishment rates. Over-wintered seeds are ready to germinate on the first warm days of late winter or early spring when humidity levels are high. In addition, hydraulic mulches are more likely to stay moist for longer periods. Hydroseeding is simpler than dry seeding because there is no seed metering system; seed mixes are simply mixed into the hydroseeder tank and applied. However, even though there is no metering system, applications can be calibrated, therefore having well-trained applicators a key for successful hydroseeding. Refer to Section 5.4.2 for more discussion on hydroseeding.

Seeding with Compost Blanket—A recent addition to seeding methods is the use of the compost blanket. This can be seed, tackifier and medium (or coarse) compost applied in a 2 inch thick layer, but because many seeds are too deep in the compost matrix, a better method is to apply a 1 ½ inch thick layer of medium (or coarse) compost with tackifer to a prepared slope, then apply another ½ inch layer of compost with tackifer and seed. A third method is to install the 2 inch layer of compost, tackifers and hydroseed on top of that. The compost when tacked in place, provides erosion control, retains moisture (but not too much, that is the reason fine compost is the wrong material for compost blankets) and the dark color of the compost captures heat that helps germination. The compost material adds organic material to the site which provides the seeds with nutrients and it jump-starts the development of a soil biotic community. On steep slopes measures may need to be taken to key the compost blanket in place, like installing straw wattles, staked in place, prior to installing the compost.

Formulate Seed Mixes

The seed mix refers to the species composition being applied over a seeding area. It is important to avoid applying a single species to a site. Because highly disturbed sites typically are extremely variable in soil temperatures, fertility, soil moisture, solar radiation, and other site factors, it is important to apply a number of species in a seed mix to ensure that all possible microsites are populated (Monsen and Stevens 2004). Microsites that are unfavorable to one species might be favorable to others. Applying a mix of species also ensures that if there is a problem with the germination of one species, the other species will fill in. The composition of seed mixes and sowing rates should be based on the growth habits of each species and the soils and climate of the site.

It is preferable to avoid mixing slow-growing species with fast growers because the fast growers will out-compete the slow growers for space and resources (Monsen and Stevens 2004). Separating slow growers from fast growers is not always possible. The seed quantities should therefore reflect higher ratios of slow growers to fast growers to achieve some degree of success. Shrubs and trees are typically less aggressive than grasses during the establishment phase and should be applied in a separate mix or planted as seedlings. Grasses tend to be more aggressive than forbs. However, if the Truax® seed drill is used, they could be applied in the same area but in different rows using the separate seed boxes. Although this does not guarantee that the grasses won't out-compete the forbs therefore the preferable approach is to seed the forbs separately if possible (e.g. forb "islands" or patches). Some species take several years to develop. A mixture of fast-growing annuals and slow-growing perennials will ensure that there is cover the first year, yielding to more robust perennials in the succeeding years.

Disturbed reference sites can be good indicators of species that are adapted to the climate and soils of the project area. Vegetative surveys conducted during the planning stages should show the proportions of species that can be expected, and these findings should become the basis for developing species composition and ratios of each species. Prior to determining sowing rates, the proportion of each species within each seed mix should be set. This information will be used to determine seeding rates for each species.

Determine Sowing Rates

The sowing rate is the amount of seeds of each species in a seed mix that are applied in a given area. Sowing rates are calculated for each species that compose a seed mix. These calculations are performed twice—once during the development of seed increase contracts to obtain an approximate quantity of seeds to propagate for the entire project, and several months prior to actual seeding when seed inventories are known and exact seeding areas are located. The calculations made prior to seeding will be used to assemble the seed mixes for each seeding area.

Each species requires a set of data to calculate the total pounds of seeds needed in a seed mix, which includes the following:

• Pure live seeds per pound of bulk seeds
• Estimated first-year survival
• Target first-year seedling density for all seeded species
• Percentage of density composed of each species
• Area that will be seeded with seed mi

Figure 5-92 shows one method for calculating the amount of seeds needed of each species in a seed mix. Because a seed mix is comprised of several species, calculations should be performed on each species. In this example, blue wildrye (Elymus glaucus) is one of several species included in a seed mix. The end result of these calculations is the number of pounds of blue wild rye seeds that should be added to each seed mix bag.

Pure Live Seeds per Pound(PLS/lb)—When purity and germination are multiplied together and divided by 100, the resulting value is the percent PLS. This represents the percentage of the gross seed weight that is composed of viable seeds (Figure 5-65). For example, if germination is 89 percent and purity is 92 percent, the PLS would be 82 percent. When PLS is multiplied by the number of seeds per pound, the result is the pure live seeds per pound of gross seeds (PLS/lb). This value is often used in seed and sowing calculations, and it states the approximate number of seeds that will germinate in a pound of bulk seeds under ideal (test) environments. For example, the PLS in Figure 5-92 is 82 percent, and the number of seeds per pound is 128,000. The total PLS/lb is ( 82 / 100 ) * 128,000 = 104,806 (Line D in Figue 5-92). Tests for purity, germination, and seeds per pound are conducted by State Certified Seed Testing Laboratories and obtained from the seed producer or supplier.

First-Year Survival—Not all viable seeds develop into established seedlings after being sown on a disturbed site. The conditions encountered on revegetation sites are generally unfavorable for germination and plant establishment. The first-year survival factor reflects the effect of the harshness of the site on plant establishment (Line E Figure 5-92). It is a prediction of the percentage of PLS that germinate and become established plants after the first growing season. A favorable site, for example, will have a high survival factor because a high percentage of live seeds will germinate and establish into plants; a harsh site will have a low first-year survival factor because seeds will germinate poorly, resulting in plants less likely to survive over the dry summer months. Unfortunately, there are currently no established field survival factors for the western United States. Therefore, the designer will have to make estimates based on experience and an understanding of site factors, seed handling, and sowing methods.

How much fall down actually occurs? Even under very controlled growing environments, such as those found in seedling nurseries, survival factors are much lower than most would think. It is not uncommon for bareroot seedling nurseries to set first-year survival values between 65 and 75 percent (USFS 1991). Compare the highly controlled environment of a nursery to seeding in the wild, where precipitation is intermittent and soils are depauperate. Only 10 to 20 percent of the live seeds sown in the wild actually turn into live plants the first year after seeding (Monsen and Stevens 2004; Steinfeld 2005).

Estimating first-year survival is always a guess. It is interesting that very exact data from seed tests are used for a portion of the sowing calculations, followed by a broad approximation of how well viable seeds will actually germinate and become established in the field. Unfortunately, this information is hard to obtain. Monitoring data collected in the spring and fall, after the completion of each seeding project, can be used to develop a basic understanding of how seeds perform in the field under various soils, climates, and mitigating treatments. First-year monitoring that measures seedling density is useful in this regard. The number of seedlings can be counted in a series of photoplots, and the average number of seedlings per square foot can be calculated. The average seedling density, divided by the average number of PLS sown per square foot (Line H of Figure 5-92), provides the survival factor for that project area. Steinfeld (2005) performed this type of monitoring for several seeding projects six months after sowing on southwest Oregon sites and found the results to be very low (15 percent of viable seeds became established plants). If this type of assessment is conducted over a range of seeding projects, survival factors could be developed for a range of soil and climate conditions. It would be good to understand how survival factors change with different types of seed-covering methods.

Factors to consider when estimating field survival are listed in Table 5-18. Sites with low first-year survival would have a large number of limiting factors. Very poor sites can have survival factors below 5 percent, whereas favorable sites can have factors as high as 20 percent.

Target First-Year Seedling Density—The target first-year density is the number of plants/ft2 desired the first year after sowing (Line F of Figure 5-92). Establishing target density factors is often based on the objectives of the project. For example, projects where the objective is fast plant establishment for either erosion control or weed prevention would usually require the target first-year densities to be relatively high. Target densities are also based on the growth habits of the species to be sown. Fast-growing species with large spreading growth habits would have low target densities. Shrubs and trees would have target first-year densities of less than 1 plant/ft2, whereas grasses might have densities up to 25 seedlings/ft2. Critically, these target first-year densities help to inform seeding rates. For example, shrubs might have a reduced seeding rate compared to grasses given these different target first-year densities. Moreover, monitoring sites after one year can provide a good indication of what densities can be expected from each species and what densities are most appropriate for meeting project objectives.

Understand that there is a point of diminishing returns, where applying more seeds does not necessarily produce more seedlings. There is a limit to how many seedlings can survive on a site, and no amount of seeds applied will change this fact. While applying excess seed errs on the conservative side, it can be wasteful and costly. It can also favor the aggressive species over the less aggressive species (Monsen and Stevens 2004). When using high seeding rates, it is important to reduce the ratio of aggressive species to non-aggressive species to ensure that non-aggressive species can become established.

Target Composition—The target composition is the proportion of each species that will comprise the seedlings found in a given area (Line G of Figure 5-92). An example of a target seed mix composition is one that would produce a stand of grass and forb seedlings comprised of 35 percent blue wildrye (Elymus glaucus), 35 percent California fescue (Festuca californica), and 30 percent common yarrow (Achillea millefolium). Refer to Section 5.4.1, see Formulate Seed Mixes for further discussion.

Area to Seed—The area to seed is the total acreage of a seeding area to which a seed mix will be applied (refer to Section 5.4.1, see Identify Seeding Areas, for a discussion on how seeding areas are determined).

Prepare Seed Mixes

Once sowing calculations are completed for each species, seed mixing operations can begin. The objective of these operations is to put together seed mixes in packages that are organized, easy to handle, and ready to use. This is an important step because there can be no room for confusion in seeding operations or time for reorganizing seed mixes. The seed mixing operation involves weighing seeds from each species or seedlot, mixing seedlots, placing seeds in bags, and labeling.

The seed bag is the basic handling unit used in seeding. Before mixing begins, determine how much area a bag of seed mix will cover. This will depend on the seeding method. For hydroseeding contracts, seed bags can be no larger than the area a slurry unit will cover (Section 5.4.2). For example, if a 1,000-gallon hydroseeder tank covers a quarter acre, then the bags of seed mix would have enough seeds to cover a quarter acre. In this example, the seed mix is divided into four bags per acre (Line L of Figure 5-92). The most typical seed bag coverage is a quarter of an acre because of the increased flexibility, reduced weight, and ease of handling.

The sowing method is an important factor in assembling the seed mix. If the mix is to be used in a seed metering system (Inset 5-19), each seedlot should be thoroughly mixed together to ensure a uniform distribution of seeds of each species on the site. However, if the seed mix is placed in a hydroseeder, it is not necessary to mix the seeds because all seeds will eventually be mixed in the hydroseeder before application. Other packaging will be required if more than one seedbox is used (e.g., the Truax® seed drill).

Drilling different-sized seeds may also require two or more seed boxes. The Truax® seed drill has three seedboxes that are adjusted to sow various seed sizes and shapes.

Other materials can also be included in the assembly of the seed mix. Mycorrhizal inoculum can be mixed with the seeds, as well as dyes to make seeds easier to see after seeding. Mycorrhizal inoculum and dye will change the rates that seeds will flow. Seed metering systems will have to be calibrated for these materials. Very small-seeded species may need to be sown with carriers, such as rice hulls (Stevens and Munson 2004). For small, fluffy seeds, wheat bran can be added to help prevent them from migrating upward in the seed mix (Dixon and Carr 2001b).

When calibrating seeds for mulch blowing operations, it will be necessary to create more small seed bags that represent smaller calibration areas (Inset 5-20).

Determine Seeding Date

The best date to sow varies by site and by species. For example, it may be preferable to seed warm season gasses (that grow most vigorously during the spring and summer) in the spring. Whereas it may be preferable to seed cool season grasses (that grow most vigorously during the spring and fall) in the fall. But typically, especially in the western US, fall sowing dates are common. On cool, arid sites, seeding later in the fall is better to prevent premature germination prior to the onset of winter (Monsen and Stevens 2004). On warm, moist sites (e.g., often found in the Midwest US), sowing can take place in the late summer and early fall, anticipating that seeds will germinate with early fall rains and become established prior to winter. If seeds are sown in the spring or early summer, seed mixes should be composed of species that germinate quickly and do not require a long natural stratification period.

Ensure Quality

There are several factors to monitor during seeding to ensure operations are administered correctly. Depth of seed placement, uniformity in application, target seed densities, and seed handling should be monitored throughout the process. It is important to periodically measure seed depths, especially at the beginning of the operation or when any new site is being seeded. Seed dyes are sometimes applied to make seeds more visible. However, these are not useful when seeds are applied through hydraulic seeders or mulch blowers. Uniformity of seed application can be monitored as seeds are being distributed through seed metering or delivery systems. Sometimes seed systems plug or malfunction, resulting in sporadic application of seeds. Poorly applied seeds, where the applicator either misses spots or applies over seeded areas, will also result in an uneven application.

Seed densities can be monitored indirectly by measuring the area where a known weight of seed has been applied and matching it to the estimated acreage it was targeted to cover. For example, on a project where a seed mix is split into quarter-acre bags, the area seeded with one bag of seed mix would be measured. If a quarter-acre bag covered only 0.2 acre, the seed was sown more thickly and the density was increased by 25 percent ( 0.5 / 0.2 ). If the seed bag had been applied over 0.30 acre, the seeds would have been spread across more area and the seed density would have decreased by 17 percent ( 0.5 / 0.3 ). These measurements should be done as each seed mix is being applied. If there is a significant change in density, adjustments to the seeding operations can be made.

Measuring a seeding area unit is important not only for determining if seeding rates are being applied correctly, but also for accurately paying the seeding contractors. Contract administrators should be measuring the area that each seed bag or known seed quantity is being sown during, or immediately after, seed application. Table 5-1 describes a method to measure area by measuring the slope length that has been seeded at each road station marker and multiplying it by the distance between markers.

Proper seed handling should also be monitored. Seed bags should be stored in suitable conditions and always handled with care. Seed bags should not be thrown or dropped or left in unsuitable conditions.

5.4.2 Hydroseeding

Introduction

Hydroseeding is a method of hydraulically applying seeds, stabilizers, and soil amendments to the surface of the soil for the primary objective of revegetation. Although the term hydromulching is often used interchangeably with hydroseeding, there is an important distinction: hydromulching is the application of hydraulic mulch and surface stabilizers for the primary purpose of erosion control. Hydromulching is typically conducted on multi-year construction projects when surface soils need to be temporarily stabilized for soil erosion or dust abatement. While hydromulching and hydroseeding operations both should stabilize the soil surface, hydroseeding has the additional and overriding goal of placing viable seeds in a surface environment to germinate and grow into healthy plants. Meeting the dual objectives of erosion control and plant establishment in one operation is often a balancing act. The best methods for soil stabilization are not always optimal for seed germination and plant growth. This section focuses on hydroseeding, not hydromulching, and the discussion includes how to best meet the needs of early plant establishment using hydraulic sowing methods. For information regarding the stabilization of the surface through hydromulching, refer to the many articles on this subject and to the manufacturers of hydromulching products.

Hydroseeding equipment is composed of a tank that holds a slurry of water, seeds, soil amendments, and stabilizing products; paddles or agitation jets in the tank to mix the slurry; a high-pressure pumping system; and a hose and nozzle (Figure 5-93).

Tanks come in a variety of sizes, from a few hundred gallons to more than 3,000 gallons. As the size of the tank increases, the speed and efficiency of the operation improve. Because the travel time is the same for any size hydroseeding unit, the farther the water source is from the project site, the more efficient larger tanks become.

The hydroseeding tank is analogous to a large mixing bowl filled with various ingredients and blended together with water to make a slurry. Typical hydroseeding ingredients fall into these categories:

• Seed
• Hydraulic mulch
• Tackifier
• Fertilizer
• Soil amendments
• Dye (typically in the hydraulic mulch)

The mixture of ingredients is called a slurry. When a slurry is applied to an acre, it is referred to as a slurry unit. The quantity of each material added to a slurry tank is only limited by the ability of the mixture to be pumped through a hose and shot through a small nozzle without clogging. The tank can only hold so much material before the mixture becomes too thick to pump. Finding the right mix and rates of ingredients is important for efficient use of the equipment. The applicators and manufacturers of these products can recommend optimum product rates.

Hydroseeding ingredients should be thoroughly blended prior to application to achieve uniform seed coverage. The two types of hydroseeding mixing systems are those that mechanically stir and those that mix using a hydraulic jet. The first system employs rotating paddles to blend the slurry in the tank and a centrifugal pump or positive displacement gear pump for slurry delivery. The second system uses a centrifugal pump to both agitate the slurry and deliver the slurry to the site. However, there is anecdotal evidence that these centrifugal pumps might be more likely to damage seed. It is suggested that designers discuss the type of hydroseeder mixing system that a contractor might use and perhaps adjust seed mixes to account for the potential increased seed damage in a centrifugal pump.

During application, the slurry is pumped to the nozzle for application. The applicator has a choice of nozzles, use of which depends on the site and slurry conditions. Slurry application can be from a "gun" mounted on the top of the hydroseeding unit or from a hose pulled manually to the application site. Stationary application (using a hydroseeding gun) is accomplished where the hydroseeding equipment can easily access the site. These areas are typically cut and fill slopes. Depending on the consistency of the slurry, the pumping system, and wind conditions, slurry can be shot 200 feet or more. Hoses are laid out for sites that cannot be reached this way. Depending on the diameter of the hose and the pumping system, hoses can reach sites more than 300 feet from the hydroseeding unit.

Hydroseeding is used when other seeding methods are impractical (Section 5.4.1). Typically, these are steeper sites where ground--based seeders are limited. Hydroseeding has the advantage over other seeding methods of applying soil amendments, fertilizers (with non-native species), soil stabilizers, and seeds together in a multi-step application. In addition, seeds that are used in hydroseeding operations do not have to be as clean (that is, free of straw, awns, chaff) as for other seeding methods. This can reduce the cost and time associated with seed-cleaning operations.

The time it takes to hydroseed is a function of the size of the mixing tank, the proximity of a suitable water source and the amount of hydraulic mulch that is applied on a per acre basis (Figure 5-94). The amount of hydromulch applied varies with aridity, slope, and soil characteristics of a given site. The greater the amount of hydraulic mulch applied per acre, the longer it will take. For example, it takes almost twice as long to apply 2,000 lb/ac of hydraulic mulch through hydroseeding equipment as it does to apply 1,200 lb/ac. For this reason, determining the appropriate amount of hydraulic mulch is important from a cost standpoint. Cost includes not only the cost of purchasing the product, but also the time to apply it. Tank size is also an important factor in application rates; the larger the tank, the less application time it takes. A 3,000-gallon mixing tank, for example, takes less than half the time to cover an acre than a 1,000-gallon tank.

Hydroseeding in wildland revegetation has a number of limitations (Stevens and Monsen 2004) that may have relevance in roadside revegetation for pollinators:

• Some seeds may not be placed in the soil depending on application method
• Seeds and seedlings can dry out
• Some seedlings cannot grow through paper fiber type of hydraulic mulch
• Seeds can be damaged by agitators and pumps
• Precocious germination can occur as a result of moisture in the hydraulic mulch
• Hydroseeding requires large quantities of water

With good planning, implementation, and monitoring, many of these limitations can be managed, resulting in successful revegetation. Ultimately, the success of any hydroseeding project comes down to the availability of water during germination and seedling establishment. As with other seeding methods the timing of hydroseeding applications should be determined in part by the climate at a project site. Hydroseeding is successful in the landscaping business because seeds are irrigated after hydroseeding until a stand of grass has become established. As one applicator stated, "what people don't understand is you can do the best hydroseeding job in the world but if they don't water it, it's not going to grow" (Brzozowski 2004). The challenge in roadside revegetation is that, for most projects, irrigation is not available. To make hydroseeding successful, strategies should be developed that maintain moisture around the seeds and in the soil during early plant establishment.

Integrate Hydroseeding into Revegetation Strategy

From a revegetation standpoint, hydroseeding serves as a method of seed placement, a means of stabilizing the soil surface for controlling erosion and to allow seedlings to become established, and a way to apply fertilizers and other soil amendments. These objectives cannot always be met in one hydroseeding operation. It often requires that each objective be considered independently and then integrated into an overall strategy. Clarifying objectives, based on the site-specific conditions of the project, and determining the best way to achieve them using hydroseeding equipment as part of the approach will lead to the best revegetation results. For example, seed placement and fertilizing are different objectives, yet meeting both objectives is often accomplished in one hydroseeding operation out of convenience. However, the best time to apply fertilizers on many projects is after the seeds have germinated (Section 5.2.1). Instead of meeting fertilizer and seeding objectives in one hydroseeding operation, separating them into two different applications would be a better strategy for meeting overall project objectives.

On a site with high surface rock, for example, the main objective would be seed placement. Little importance would be placed on surface stabilization because the rock has already created a stable surface. The best potential sites for seedling germination on this harsh surface would be between the surface coarse fragments where seeds are protected and moisture collects. Yet a common mistake that occurs in many hydroseeding projects is to include the same rates of tackifiers as would be used on a soil surface. Under these circumstances, tackifiers adhere seeds to the rock surface, preventing the seeds from washing between the gravel and cobbles that cover the surface. The objective of stabilizing the surface is not only unnecessary in this example, it would negatively affect placement of seeds.

Hydroseeding should always be accomplished within a strategy of creating an optimum seed environment. The hydroseeding operation places seeds on the surface of the soil, which is often a poor environment for germination. Hydraulic mulch is inferior to long-fiber mulches in reducing surface temperatures, maintaining soil moisture, and moderating surface temperatures, especially in more arid climates (Section 5.2.3). The term "hydraulic mulch" is misleading because some materials that fall into this category like paper fiber mulch, lack many of the important properties associated with mulches (Section 5.4.2, see Select Hydraulic Mulch and Determine Rates). By their nature, hydraulic mulches are more like a growing medium than mulches because of their capacity to absorb water (most hydraulic mulches hold greater than 1,000 times their weight in water). As a growing medium, hydraulic mulch maintains high moisture around the germinating seeds, but once the hydraulic mulch dries out, which is often very quickly on dry sites, it no longer protects the seeds from drying as a mulch would and germination rates are compromised.

The literature is scant and inconclusive on the benefits of hydraulic mulch to seed germination and seedling establishment in wildland conditions. Carr and Ballard (1980) found no difference in plant establishment when seeds were applied with and without hydraulic mulches, but only low rates of hydromulches were compared. One approach to increasing seed germination that is often used in drying climates is a two-pass application system where seeds and a minimum amount of hydraulic mulch are applied in the first pass, and then covered by a thick application of hydraulic mulch in a second pass. While this application method appears to have some advantage over a one-pass operation because the seeds are covered with a greater thickness of hydraulic mulch, it is not known what the difference in germination and seedling establishment rates might be. The benefits from a germination standpoint are probably not seen until the hydromulch rates are high (3,000 lb/ac or greater). Even then, on arid sites receiving less than 6 inches precipitation, higher hydraulic mulch rates can intercept the low amount of precipitation that is received, preventing moisture from reaching the seeds (Section 3.8.1, see Rainfall Interception). Because it is uncertain whether hydraulic mulches improve germination, it is better to base mulch rates on surface stability objectives than on seeding objectives and use other methods to improve seed germination. For example, it might be more effective to reduce the amount of hydraulic mulch to the minimum amount necessary to apply seeds and, with the costs savings, apply a long- fibered mulch in a second operation.

Identify Hydroseeding Areas

Hydroseeding should take place after the final slope shaping and topsoil placement have been completed. Several months before hydroseeding is to occur, the site should be visited to finalize an implementation plan that includes the locations of where the plants or cuttings are to be installed and where seeding will take place. While most of the hydroseeding areas will conform to the revegetation units developed during planning, the site always looks different after construction. In this field review, the exact locations of the areas that will be hydroseeded are drawn on a road map and areas are identified where different seed mixes, fertilizer types/rates, or hydraulic mulch rates will be applied.

The acreage for each hydroseeding area is calculated using methods described in Table 5-1. This method partitions the cut and fill slopes into rectilinear units by road stations and calculates acreage between each unit. This information is then summarized in a hydroseeding table (shown in Inset 5-21) that is used to develop task orders. It can also be used in the field for keeping a record of acreages and the location of hydroseeding operations.

The proximity to streams should be considered when locating hydroseeding areas. If hydroseeding areas are adjacent to ditches or waterways that drain into live streams, a buffer should be included around these features to avoid fertilizers entering the stream system. Fertilizers applied to these sites have the potential of entering ditches during rainstorms and eventually reaching a stream course as nutrient pollution. Road runoff can be a significant contributor of nutrients to water systems (Reuter and others 1998).

Determine Seeding Rates

Sowing rates for hydroseeding are calculated using the same method outlined in Figure 5-92. The designer is referred to this section for determining seeding rates for any type of sowing method. These sowing calculations assume that the method of sowing does not damage the seeds. This might not be a good assumption with hydroseeding, which has been shown to increase the risk of seed breakage in the hydraulic seeder tank during mixing (Kay and others 1977; Wolf and others 1984; Pill and Nesnow 1999). Additions of fertilizers further increase the risk by exposing seeds to high salt levels when seeds are in the slurry tank and also after they are applied to the soil surface (Brooks and Blaser 1964; Carr and Ballard 1979; Brown and others 1983). Taking precautions to reduce the risk of seed damage during hydroseeding will increase the seed germination rates and reduce the amount of seed needed for the project.

Considerations that can reduce the risk of damaging seeds include the following:

• Type of hydraulic seeder
• Seed condition
• Duration in slurry
• Seed moisture
• Hydraulic mulch
• Nozzle and nozzle position
• Fertilizers

Hydraulic Seeders—Hydraulic seeders that use centrifugal pumps for agitation and delivery can have a higher potential to damage seeds than systems with paddles and rubber-coated gear pumps (Kay 1972a; Kay and others 1977). Kay (1972a) found that germination of intermediate wheatgrass (Agropyron trichophorum) seeds was reduced from 80 percent (control) to 10 percent germination after one hour in a centrifugal agitation system; after two hours, germination was reduced to 1 percent. There was no reduction in germination after one hour using paddle agitation, but germination declined to 59 percent after two hours. Pill and Nesnow (1999), however, found that centrifugal pumps did not reduce germination rates of Kentucky bluegrass (Poa pratensis) and perennial ryegrass (Lolium perenne) after mixing for an hour in a slurry tank.

Seed Condition—Grass seeds are enclosed by sets of bracts, called the lemma and palea. These structures provide a protective covering (Figure 5-95) and are believed to reduce seed breakage during hydroseeding agitation and application. In the aforementioned study, Pill and Nesnow (1999) believed that one of the primary reasons there was no decline in germination after an hour of mixing in a slurry tank was because the lemmas and paleas were still intact around the seeds. The association between presence of these seed structures and protection from seed breakage during hydroseeding should be considered when cleaning seeds for hydroseeding. Seed cleaning is necessary for storage and seeding (Section 5.3.1 and Section 5.3.4). However, seeds for use in hydroseeding operations do not have to be as clean as seeds used in other seeding methods. Each species has different cleaning requirements for hydroseeding. Some require thorough cleaning, while others might require very little cleaning. It would be beneficial to discuss the level of seed cleaning for hydroseeding with seed extractory personnel and seed increase contractors.

Duration in Slurry—The longer seeds are mixed in the slurry tank, the greater the potential for breakage. Kay and others (1977) found that after 20 minutes of agitation, seed germination decreased significantly for Bermudagrass (Cynodon dactylon) (Figure 5-96). For this reason, it is important to add seeds immediately before application.

Seed Moisture—As a general rule, moistened seeds have less potential for breakage than dry seeds because they are more flexible when impacted. Kay and others (1977) found that soaking Bermudagrass seeds for 1.5 days prior to application significantly increased germination over dry seeds (Figure 5-96). Longer soaking periods (4 days) had negative effects on germination because radicles were emerging and were damaged with mixing.

Soaking seeds prior to hydroseeding will unfortunately initiate seed germination, which is not usually desirable for hydroseeding projects. Pill and Nesnow (1999) suggest seed priming as an alternative to soaking. Priming is a seed treatment that partially moistens seeds without initiating seed germination (Pill and others 1997). Seed is mixed at 1 part seed to 10 parts moist vermiculite (although peat could be used as a substitute) and stored at cool temperatures for up to 10 days prior to hydroseeding.

Hydraulic Mulch—Hydroseeding without hydraulic mulch can increase seed damage (Kay 1972a, 1978). Using a minimum rate of 500 lb/ac hydraulic mulch is suggested for protecting seeds (Kay 1978).

Nozzle Type and Nozzle Position—Shooting slurry straight at the soil in close range can damage seeds. The impact at high speeds can cause seed coats to break. As one hydroseeding operator describes the action, "we just shove that seed right smack in the ground with a lot of force...the gun was slamming straight to it" (Brzozowski 2003). Describing this action to a Forest Service seed extractory specialist, his reaction was, "that can't be good for the seed" (Barnar 2007). In the seed production and seed extraction businesses, handling seeds carefully is a high priority. This attitude and practice should not stop with the seed producers, but follow through to the application of seeds. One application practice that could reduce seed damage is to aim nozzles so the slurry is not hitting the soil surface with full force at close range. Arching the slurry stream so the spray hits with lower force is more desirable. Using less pressure or lower pressure nozzles, such as fan nozzles, can also reduce seed damage (Figure 5-97). Some soils are very loose or powdery after construction, which can cushion the seeds, as opposed to very compacted surfaces. Seeds applied to these surfaces can be buried under the loose soil when the slurry is shot straight at the surface, offsetting the effects of seed breakage and increasing germination potential (Mast 2007).

Fertilizers—Adding fertilizer to the slurry can reduce germination of certain species due to the effects of fertilizer salts on seed imbibition, or uptake of water (Figure 5-98) (Brooks and Blaser 1964; Carr and Ballard 1979; Brown and others 1983). This is not just a problem when seeds and fertilizers are mixed together in the slurry tank; it can also negatively impact the seeds after they are applied to the soil surface and before the first rains dilute the surrounding salts. Effects of fertilizer salts are more detrimental on sites with low rainfall. Carr and Ballard (1979) found white clover (Trifolium repens) and, to a lesser degree, Festuca spp. had the greatest reduction in germination (Figure 5-6). They suggest white clover should be applied by hand, separate from the hydroseeding operation.

Assuming that most native seeds, especially legume species, are affected by fertilizer salts, it is important to understand what the effects of different types and rates of fertilizers will have on the salt concentrations in the slurry. Brooks and Blaser (1964), Carr and Ballard (1979). And Brown and others (1983) used inorganic, fast release fertilizers, which dissolve quickly in solution (Section 5.2.1). Organic and control release fertilizers, however, dissolve slowly and therefore should have lower salt levels in solution. Whichever fertilizers or rates are used, testing the slurry for soluble salts should be conducted to ensure that concentrations are not lethal (Section 3.8.4, see Salts).

The effect of hydroseeding operations on seed viability is an important issue and deserves more research attention. Monitoring information can be used to broaden understanding on how to properly use this important tool.

Select Hydraulic Mulch and Determine Rates

Hydraulic mulch is a low bulk density material applied through a hydraulic seeder to increase surface soil strength and reduce erosion. At high application rates, seeds are covered, thereby increasing the potential for increased seed germination. Commercial hydraulic mulches are derived from wood fiber, recycled paper (wood cellulose), sterilized grass straw synthetic fibers, mechanically treated wood fibers, or combinations of these. Wood fiber mulches are manufactured from wood chips thermally treated by a steam and high pressure shredding process; wood cellulose mulches are made from waste paper materials such as recycled newspaper and cardboard (Trotti 2000). Hydraulic mulches typically have very high water-holding capacities (over a 1,000 times their weight in water). A pound of wood fiber mulch, for example, absorbs between 1.5 to 2.5 gallons of water and, inversely, a gallon of water holds between 0.40 and 0.66 pound hydraulic mulch. This is important information to know when determining how much hydraulic mulch to add to a slurry tank. Most operators will not exceed a ratio of 0.4 to ensure they do not clog their system with a slurry that is too thick. At this proportion, a 1,000-gallon tank would hold 400 pounds of wood fiber mulch. Product specification sheets should indicate the ratio of hydraulic mulch to water for hydroseeding equipment.

The depth and cover of hydraulic mulch depends primarily on the quantity and properties of the mulch placed in the tank. Typical hydroseeding mulch manufacturer's application rates range in application rates from 1,000 to 3,000 lb/ac. At lower application rates (<1,000 lb/ac), wood cellulose (paper) fiber mulch will not cover the entire soil surface, leaving most seeds and much of the soil surface exposed. At the manufacturer's recommended application rates or higher (>3,000 lb/ac) the soil surface and seeds are usually completely covered (Figure 5-99). A class of higher strength mulches, purposefully manufactured with the tackifiers and tracer dye, called bonded fiber matrixes (BFM) are applied at rates above 3,000 lb/ac. Correctly applied this BFM can bond together to form a continuous mat given that fiber length is typically longer in these products. A BFM will stabilize seeds and control surface erosion up to a year after application depending on site conditions. Even more robust than BFM, High Performance Growth Media (HPGM) consists of engineered and mechanically kinked fibers that interlink when applied to soil. When applied correctly, sprayed from two different directions at the specified application rate, and achieving complete coverage, the HPGM becomes, in effect, a hydraulically applied erosion control matting as well as a growth media for seeds. Correctly applied wood fiber HPGM has a functional life of about a year and a coconut fiber HPGM has a functional life of two years although fiber longevity will vary by site specific characteristics such as soil type or canopy cover.

The length of the wood or cellulose fibers is an important characteristic in creating a soil cover mulch that does not restrict seed germination or plant growth. Cellulose mulches have shorter fibers than wood fiber mulches and, therefore, these materials compact much easier when they are applied. Applying too much cellulose mulch can result in a soil surface that has the consistency of "paper mache." At application rates greater than 1,500 lb/ac cellulose mulch, there is a reduction in infiltration and air exchange, and seed germination and seedling establishment are decreased (Gassman 2001). Some manufacturers have overcome this problem by mixing straw, a long-fibered material, with paper mulch. Typically, cellulose mulch requires 20 to 40 percent more material to achieve the same uniformity of coverage as wood fiber mulch (Trotti 2000) (Figure 5-100). While recycled paper mulches are typically less expensive than wood fiber, the cost savings are partially offset by the increased amount of paper mulch used. Blended mulches (those with equal portions of wood fiber with recycled paper) are an effort to improve the characteristics of recycled paper by adding wood fiber.

Typically, paper a fiber or cellulose fiber mulches are the lightest duty mulches which are best used on flat or gently sloping surfaces. This mulch should be applied at the manufacturer's recommended application rate (1,000-2,000 lb/ac). This mulch has issues in that it provides little in the way of erosion control, it can form a paper mache like crust that some seeds cannot penetrate and it lays down in a dense layer with little pore space which when dry can wick moisture from the soil. Wood fiber and straw derived hydromulches provide little in the way of erosion control and should also be used on gently sloping surfaces. These mulches are installed at a manufacturer's recommended application rate of about 2,000 lb/ac. When correctly installed they have enough loft to allow seedlings to penetrate through the mulch. They hold some moisture which aids germination but provide little in the way of thermal regulation of the soil. The BFM and high performance growth media (HPGM) are manufactured to have long and short fibers that are mechanically treated so that they interlink with open pore space, when applied at the recommended application rate, which can be as high as 4,500 lb/ac. These products are generally packaged with tackifier and tracer dye for accurate use. They can provide excellent erosion control and can be used on slopes of 1:1 or steeper. It is recommended that these materials be used in a multi-step process with the seed and minimal mulch be sprayed on in the first pass, then the rest of the mulch cover the seed in two following passes from different directions so that the seed is in good contact with the soil and the mulch forms a contiguous layer covering the seed. These materials have good loft allowing seedling penetration, they have enough thickness to hold moisture help retain soil moisture and they provide a small measure of thermal regulation to the soil. BFMs and high performance growth media are the most expensive of the hydraulically applied mulches.

The use of hydraulic mulch for seed germination becomes less important on wetter sites, especially in climates where there is little soil drying during germination (Carr and Ballard 1980). These conditions are found from fall through early spring on many sites in the Coast Range and Cascade Mountains, as well as microsites that include north aspects and sites shaded by vegetation. On these sites, 1,000 lb/ac or less might be sufficient for seed germination but manufacturer's recommended application rates should be followed. In areas with high rainfall and erosive soils, a higher strength hydraulic mulch at higher application rates or even a bonded fiber matrix might be needed to keep seeds and soil in place until seeds have germinated and grown into established seedlings.

Select Tackifier

Tackifiers are sticking agents that bind soil particles together and protect the surface from wind and water erosion. When applied with hydraulic mulch, tackifiers increase the effectiveness of the mulch as a soil cover by binding the hydraulic mulch fibers and the surface soil particles together. Tackifiers create water-stable surfaces, which means they are capable of repeated wetting and drying and do not lose strength after a series of rainstorms. Hydraulic mulch and tackifiers can remain effective even through a winter with high precipitation (Figure 5-101).

Selecting a tackifier can be difficult. Numerous commercially available products are on the market from which to choose. Unless these products have been used side by side in the field, it is difficult to know the difference among them. A hydraulic seeder operator can offer advice on tackifiers and other hydraulic seeding products because they have tried a variety of products and usually have a good idea of their effectiveness. Many mulches are pre-packaged with the appropriate ratio of tackifier.

The two general types of tackifiers commonly used in hydroseeding are organic and synthetic. Organic tackifiers are derived from plant materials, which include guar, plantago, and other plant starches. Synthetic tackifiers are manufactured polymers and copolymers that include polyacrylamides (PAM), acrylic polymers and copolymers, methacrylates and acrylates, and hydro-colloid polymers. Organic tackifiers break down biologically and are typically effective for at least three months depending on site conditions and product type. Synthetic tackifiers are photo and chemically degradable and have somewhat greater longevity than organic tackifiers, lasting up to a year on many sites (CASQA 2003b).

Revegetation specialists and operators usually develop a preference for tackifier products based on ease of handling and storage, ease of application, toxicity to plants, environmental concerns, weather restrictions, and application rates.

Handling and Storage—Tackifiers are available as dry powder or liquid formulations. Most organic and some synthetic tackifiers are packaged as dry powders. These products are easy to handle and store because they weigh less and have less bulk than liquid containers. Liquid tackifiers should be stored in areas that will not freeze if stored over the winter. Handling and disposal of plastic containers are also a consideration when using liquid tackifiers.

Ease of Application—An important property of tackifiers is viscosity. Viscosity is the measure of the "stickiness" of a tackifier, or the propensity of the tackifier to hold a slurry together when it is applied. Tackifiers with high viscosity, such as guar-based tackifiers, will hold the slurry together as a fine stream when pumped from the nozzle (Figure 5-102A), and the stream of slurry will shoot farther. When a slurry with high viscosity hits the soil surface, it sticks and does not easily run off. A slurry with low viscosity, however, will separate as it is comes out of the nozzle and drift, especially if there is a breeze, resulting in uneven application (Figure 5-102B). If low viscosity slurries are applied at rates that are greater than the soil infiltration rates, the slurry will run off the surface. Not only will seeds be lost, but other materials in the slurry (including fertilizers) could enter surface drainage systems (Figure 5-102C).

Tackifiers act as lubricants and create less friction through the hydraulic equipment. With high viscosity tackifiers, equipment runs smoother and nozzles do not plug as frequently. This will enhance the overall performance and longevity of the equipment.

Toxicity to Plants—One reason organic tackifiers are sometimes preferred over synthetic tackifiers is the belief that these materials are better for seed germination and seedling establishment. They are organic substances that break down into non-toxic compounds. While organic tackifiers are sometimes advertised as being better for plant health, there is nothing in the scientific literature to indicate that synthetic tackifiers are any more harmful or toxic to plant establishment than organic tackifiers.

Environmental Concerns—There have been concerns about the use of polyacrylamides (PAM) on human health and the environment. Acrylamide, a known neurotoxin to humans, is the main ingredient of this polymer. Polyacrylamides alone have low toxicity—LD50 of 5,000/kg oral dosage (Peterson 2002). However, in the manufacturing of the polymer, some acrylamide is formed. The U.S. Food and Drug Administration has set a maximum allowable acrylamide content in PAM of 0.05 percent. While PAM does not appear to break down in the environment to acrylamide if released during decomposition, it is thought to be quickly decomposed by soil microbes (Peterson 2002). Furthermore, because PAM degrades slowly in the environment, there should not be an accumulation of acrylamide in the soil (Claassen and Hogan 1998). Evans (2006) cites reviews by Barvenic (1994) on health hazards and Goodrich and others (1991) on aquatic macrofauna, edaphic microorganisms, or crop species. When polyacrylamides were applied at recommended rates, the materials were found to be safe for the environment. The designer is referred to Barvenik (1994) for a comprehensive discussion of PAM in the environment.

As with all products used in revegetation, a Material Safety Data Sheet should be requested from the manufacturer of the product and reviewed for possible human effects and effects to the environment. Some states have regulations on the use synthetic polymers in landscaping. It is important to be abreast of the latest environmental regulations (Peterson 2002).

Weather Conditions—Tackifiers have limitations and conditions for proper application, including soils should be moistened prior to application; there should be a 1- to 3-day drying period after application; the site cannot freeze during or immediately after application; or they should be applied between a certain temperature range. It is important to understand which environmental restrictions apply to the tackifier being used and how it might affect the hydroseeding operations. A site that is expected to be wet in the fall, for example, will require a tackifier that needs a minimal curing period.

Tackifier Rates—When tackifiers are used with hydraulic mulches, they are applied at rates at 5 to 10 percent of the weight of the hydraulic mulch (CASQA 2003a). Refer to manufacturer labels for specific rates.

Select Other Slurry Components

The remaining components of the hydroseeding slurry can include dyes, fertilizers, biostimulants, and mycorrhizae.

Dyes—Dyes are used as markers for the applicator to indicate where the slurry has been applied. Most hydraulic mulches include dyes, so it is not usually necessary to include dyes in the slurry when using these mulches.

Fertilizers—Fertilizers are often applied through hydroseeders. Determining the type and amount of fertilizers to use is discussed in Section 5.2.1.

Biostimulants—Biostimulants are sometimes applied to the slurry.

Mycorrhizae—Mycorrhizae are often included in the slurry (Section 5.2.7).

Locate Water Source

Hydroseeding cannot be conducted without a water source, yet a common mistake is to wait until the last minute to locate such a source. For many parts of the western United States, water sources can be long distances from the project site. It is important to establish where water will be obtained for hydroseeding early in the planning process. Considerations when selecting a water source include the following:

• Distance—On projects where the water source is a long distance from the hydroseeding site, large slurry tanks will increase the efficiency of the operation. Conservation of water should be a priority in these circumstances. Covering more area with each slurry tank is one way to reduce water needs. This can be accomplished by applying lower rates of hydraulic mulch and tackifier per acre.
• Water quality—The quality of the water for hydroseeding should be low in salts and other potentially toxic compounds. If in doubt, send a sample to a water quality lab for testing or, at minimum, run pH and conductivity measurements on a sample.
• Water use permits—Always check with the agency or landowner for permits to use their water.

Develop Hydroseeding Contract

Once a basic hydroseeding plan is developed, a contract is developed. The contract usually contains most of the following elements:

• Site location and description—A general description of the site, slope gradients, location, and time of year the hydroseeding will occur should be addressed.
• Products and rates—The hydroseeding products or equivalent products (hydraulic mulch, tackifiers, fertilizers, etc.) are identified, and the rates per acre for each product are stated for each hydroseeding mix or mixes. The total number of acres for each hydroseeding mix should be tabulated.
• Water source—The location and distance to each water source are described. The contract should indicate whether it is the responsibility of the contractor to obtain agreements from owners for use or any required water permits.
• Storage area—The contractor will need a site to store hydraulic mulches, tackifiers, fertilizers, and other materials associated with the hydroseeding operation. The site should be in close proximity to the hydroseeding areas and relatively safe from vandalism.
• Equipment—If specific types of hydraulic seeders are required for the job (large tank, or tracked equipment for example), they should be specified in the contract. Using hoses to access portions of the project site will often be necessary. The contract should specify how many feet of hose are needed and what percentage of the project will be applied by hose.
• Cleaning equipment—The contract should state that the tank and hoses will be cleaned from all previous hydroseeding or hydromulching projects. The equipment will be inspected and, if it does not pass inspection, the contractor will be required to clean equipment at an approved offsite location.
• Weather conditions—The weather conditions, based on manufacturer specifications, should be stated. The contract should specify acceptable temperature ranges and wind velocities. It should also state whether rain or freezing temperatures can occur within a specified period after application. A provision should be stated that applications will not occur on frozen ground. Some tackifiers also require that soils be moistened before application.
• Mixing—The contract should state that the seeds be mixed into the slurry immediately before application. It should further state that the slurry should be applied within 30 minutes after the seeds have been placed in the tank. When the seeds are in the slurry, it should be moderately agitated only enough to mix the seeds and keep the slurry from separating.
• Application—The slurry should be applied at the manufacturers recommended application rate. Anything less than 100 percent coverage of the soil surface is incorrect application of the material. Slurry should not run off the soil. If it does, adjustments to application speeds or nozzles should Figure 5-97 and Figure 5-98 show the spray pattern of two types of nozzles. Avoid applying slurry at a range that causes slurry to splash off the surface and soil to dislodge. A two-pass method is preferred to obtain good seed coverage. In the first pass, 50 percent or less of the slurry is applied, followed by the second pass that applies the remainder of the material. Each pass is applied in a different direction (bidirectionally), which reduces the "shadow effect" created by just one pass and may serve to better lock the matrix together (Bill Mast personal communication).
• Traffic control—The contract should state how traffic safety will be ensured during application. Will the contractor be required to supply signs, warning lights, or flaggers?

Keep Good Records

Hydroseeding is a complex task. Not only are several products being applied at different rates at one time, but they should be evenly applied over large complex areas. A skilled hydroseeding operator should be at the helm, and it is important to keep track of what is being applied and the acres on which it is being applied. This will ensure that the target amount is being applied and enable accurate payment to the contractor.

The records begin with the original hydroseeding prescription. These are the planned application rates of each hydroseeding material. It is not enough to know what is wanted as a finished product on the site; it should be understand how it will be accomplished. This means that the prescribed product quantities per acre are translated into how it will actually be applied. These calculations can be challenging, especially when the hydroseeding operation is in full swing. It is better to have some idea how this will work before arriving in the field. Inset 5-21 provides a guide through the process of determining how much of each hydroseeding material should go into a slurry tank. These calculations, along with the contract specification, become the operation plans.

During hydroseeding operations, the contract inspector should keep track of each slurry tank that is applied. This includes the time, amount of water, quantities of products, location, acreage, and weather conditions. Calculating the acreage of each slurry tank is important in the field to ensure that the rates of materials are being applied as prescribed. This can be accomplished using a method shown in Inset 5-21, Table 4.

When this information is collected, the actual applied rates of materials per acre can be made using the method shown in Inset 5-21, Table 6. This will show how close each slurry tank came to the prescribed rates. This is important feedback for the hydroseeder operator. If the application rates were off significantly, adjustments can be made quickly. These records can be summarized at the end of the project to determine total quantity of materials used and the number of acres covered. This information can be the basis for contract payment.

On projects with significant earthwork, cut or fill slopes can be longer than the distance a hydroseed spray can reach. Plan seed applications so that exposed soils are seeded while they are accessible. This may require multiple visits by the hydroseeding contractor.

5.4.3 Installing Cuttings

Introduction

Live cuttings have a variety of uses in revegetation projects, from stream restoration to roadside stabilization. When live cuttings are used as slope reinforcement, barriers to soil movement, or integrated into retaining structures such as rock gabions, crib walls, or rock walls, they form the living component of a soil biotechnical engineering system (Sotir and Gray 1992). In slope reinforcement, live cuttings initially play a structural role by increasing soil strength and preventing surface erosion. As cuttings establish into plants, soils are stabilized through a dense network of interlocking root systems. Soils are further stabilized during the growing season as soils dry due to increased evapotranspiration and rainfall interception.

Soil biotechnical engineering techniques are well documented. Gray and Leister (1982), Sotir and Gray (1992), and Lewis (2000) are excellent sources on road and slope stabilization, and the designer should refer to Bentrup and Hoag (1998) for streamside stabilization. Section 5.3.2 described how to collect and evaluate live cutting quality; this section focuses on the care and installation of live cuttings to optimize the success of biotechnical engineering and other roadside revegetation projects. For simplicity, live cuttings are grouped by general application in biotechnical engineering projects as follows: live stakes, live brush layers, and live fascines.

Live Stakes

Live stakes are individual cuttings that are inserted into the slope to physically stabilize the soil and, with time, grow into individual plants with dense, interconnecting roots that further increase soil stability. Live stakes are used to repair small earth slips and slumps (Sotir and Gray 1992) and as pole plantings for stabilizing streambanks (Bentrup and Hoag 1998). Joint planting refers to live stakes inserted into voids or openings between large rocks. The live stakes can take root and revegetate rock riprap sites or portions of fractured bedrock (Sotir and Gray 1992). Live stakes are also used in live fascine installations and to anchor erosion mats to the soil (Lewis 2000). In gullies, draws, or intermittent streams, live stakes are placed in rows as live silt fences (Polster 1997) to slow water velocities and catch sediments and other debris. In saturated soil conditions, where excavation for brush layering or fascines is not feasible, live stakes can be densely stuck by hand.

Collection—Live stakes are collected from the main stems of donor plants located in the wild (Section 5.3.2) or from stooling beds in nurseries (Section 5.3.5). The optimum period to collect cuttings is during the dormant period after the plants have lost their leaves. If cuttings are collected outside this period, testing the viability of the cutting material is essential (Section 5.3.2, see Determine Rooting Potentail). It is important to collect cuttings with several dormant buds because this is where shoots will originate (Figure 5-103).

When preparing stakes, all side branches are removed, leaving just the stem. Only stems with diameters between 1 and 3 inches are used. Stems are cut into lengths of 1 to 3 feet, depending on how the materials will be used. It is important to select the appropriate cutting length. Stems that are too short will affect the success of the project, and cuttings that are too long will increase the costs of the project. During collection, basal ends of the cuttings are always oriented in the same direction to ensure that the buds will be aligned. This will help avoid confusion later when the stakes are being installed. Finding the orientation of the buds is often difficult (Figure 5-103) and having to reorient in the field takes time. As individual stakes are made, the top of the stake is cut flat, while the basal end is cut at an angle (Figure 5-104). This makes the stake easier to insert into the soil and orients the live stake so the buds are facing up and away from the soil surface. If buds are facing down, the live stake will not root.

During collection, live stakes are wrapped in small bundles with twine. The size of the bundle should be light enough to be easily carried. Once the bundle size has been determined, the numbers should not vary in order to track cutting quantities. Stakes can be cut from healthy donor plants. Stems that have obvious insect or disease damage should not be used. It is often easy to forget that live cuttings are plant materials, like seeds and seedlings, and should be handled and stored with care

Storage—It is recommended that live, dormant stakes be collected and installed the same day (Sotir and Gray 1992; Lewis 2000). This is not always possible in a road construction project. When it is not, temporary cold storage is an option. Temperatures in these facilities should be set below 40° F and, if humidifying equipment is available, it should be kept on high. For longer-term storage (over two weeks), cuttings should be wrapped in plastic or moist burlap to prevent the vegetative material from drying out and temperatures should be set just below freezing. Lower temperatures can result in damage and even death (Wearstler 2004). As a last resort, cuttings can be temporarily stored outside, provided daily temperatures are low (<50° F) and humidity is high, cuttings are completely wrapped in plastic, temperatures will not drop below 25° F, and the site is shaded from the sun.

Preparation—Studies of black willow (Salix nigra) have shown that soaking dormant cuttings prior to installation can increase survival (Schaff and others 2002; Martin and others 2005; Pezeshki and others 2005; Pezeshki and Shields 2006). Soaking for approximately 10 days appears to be the optimum period for black willow (Schaff and others 2002; Pezeshki and Shields 2006). Soaking non-dormant cuttings, however, appears to be detrimental to survival (Pezeshki and others 2005; Pezeshki and Shields 2006). Species native to the western United States might respond similarly to the black willow. The effects of soaking can be tested in other willow species using a method outlined in Section 5.3.2, see Determine Rooting Potential. If live stakes are soaked in streams, it is important to be sure they are sufficiently protected from being swept downstream during high precipitation or snowmelt.

Installation—For most applications, live stakes are installed perpendicular to the soil surface. When installed, no more than one-quarter to one-fifth of the cutting is exposed (Sotir and Gray 1992; Darris and Williams 2001). Buds are always pointing up and away from the soil surface with at least two healthy buds above the soil surface. It is essential that soil be firmly packed around live stakes so there are no large air spaces surrounding the cutting. For successful sprouting the live stakes can be installed in locations and to a depth where soil moisture is consistently available. Live stakes can be installed using the techniques described in Section 5.4.4. These include a shovel, auger, or expandable stinger. In addition to these methods, several techniques are available specifically for live stake installation, which include a hammer, stinger, or Waterjet Stinger.

Hammer or Mallet—For best results a steel rod can be used to open a hole for the live stake and the stake inserted into the hole and the surrounding ground tamped to eliminate voids. Live stakes can be pounded into the ground using a hammer or mallet but this can abrade the bark, split the stake, and provide an opening to disease or fungus. If the stake is hammered the use of a dead blow hammer is recommended and the angled basal end of the stake is placed on soft soil surface and the top of the cutting is struck. A small 2 x 4 wood block can be placed on the top to absorb the impacts and reduce the risk of splintering the stake. If splintering does occur, the splintered ends can be cut (Lewis 2000). After cutting, there should still be several viable buds above the soil surface. Using a hammer or mallet works best when soils are loose and low in rock fragments. It becomes more difficult as rock content or compaction increases. Smaller stem diameters are often not sturdy enough for this installation method.

Stinger—The stinger is a good method for installing live stakes on rocky or compacted soils. A pilot hole is created by mechanically pushing a metal rod into the soil. A live stake is inserted into the hole and tamped to the bottom using a hammer or mallet, as described above. Some operators will create the hole with the stinger and, after placement of the stake, use the face of the excavator or backhoe bucket to push the stake farther into the soil. The hole created by the stinger is often larger than the diameter of the stake, and the soil should be tamped in around the cutting to reduce air space and create good soil contact. A stinger can be made by welding a long piece of rebar to the bucket of an excavator or backhoe. The stinger is limited by slope gradient and terrain accessibility.

Waterjet Stinger—The Waterjet Stinger hydraulically creates a hole for installing live stakes. A pump draws water from a stream, lake, or water truck for delivery through a hose to the stinger nozzle. As the tip of the nozzle is pushed into the ground, high-pressure water is injected into the soil, creating a slurry (Figure 5-105). When the Waterjet Stinger is removed, a stake is quickly pushed into the resulting slurry at the desired depth. As water drains from the slurry, soil settles around the cutting, resulting in good soil contact.

The advantages of using the Waterjet Stinger are that it is simple to operate and transport; little training is necessary to use it; production rates are high; holes are deep, ensuring that cuttings are planted directly into a wet environment; soils are saturated around the cutting for a long period of time; and the soil slurry settles around the cutting ensuring good soil to stem contact, eliminating air pockets in the rooting zone (Hoag and others 2001). The disadvantage of the Waterjet Stinger is that it requires a nearby source of water. If the project is not near a body of water, it can be brought in using a water truck or large water storage containers placed in the back of a truck (Figure 5-106). The Waterjet Stinger is also limited by the amount of rock present in the soil. This equipment does not work well in soils containing gravels, cobbles, and boulders that obstruct the downward movement of the probe (Hoag 2007). Sandy soils drain quickly, so installation of cuttings with the Waterjet Stinger should be done quickly and with a little more effort. Steep slope gradients and rough terrain also limit equipment and the transportation of water. For more information on the Waterjet Stinger, refer to Hoag and others (2001).

Expandable Stinger—The expandable stinger can install live stakes into all soil types and soil conditions, from rocky to compacted. It can plant long cuttings (> 4 ft) and stems of most diameters (including very small diameters). The stake is placed into the stinger, which is inserted into the soil and released, leaving the cutting at the desired depth (Section 5.4.4, see Select Planting Tools and Methods). This installation method can leave large air spaces around cuttings. It is therefore recommended that soils be tamped around the cutting after placement.

Hand-Sticking—Hand-sticking is appropriate in areas where soils are mucky or saturated, including recent landslides and wetlands, and cuttings can easily be inserted into the soil. Because this installation method can be done quickly, areas can be planted at very high densities (Figure 5-107).

Live Brush Layers

Live brush layers are cuttings that are spread on excavated benches and covered by soil (Figure 5-108). This practice is used in several biotechnical engineering applications, including brush layers and modified brush layers. Constructing brush layers is a three-step process in which contour benches are excavated, live branches are spread across the bench surface, and branches are covered with soil from constructed benches directly upslope. The process begins at the bottom of the slope and is repeated until the entire slope is installed with brush layers. In a modified brush layer system, the brush layers are resting on, and supported by, logs or live fascines (Sloan 2001).

Brush layers and modified brush layers increase slope stability and reduce erosion by breaking slope length, reinforcing soil, trapping sediment, increasing infiltration, acting as horizontal drains, and reinforcing soil as cuttings develop roots (Sotir and Gray 1992). Live brush layers can also be used to vegetate crib walls, rock gabions, green walls, and rock walls. In this application, live branches are placed on benches that are created as these structures are built. For crib walls (Inset 5-22), live layers are placed on the bench created behind each layer of logs; in rock gabions, live layers are placed on each layer of gabion baskets.

Collection—Materials for live layering are obtained from branched cuttings collected in the wild or from stooling beds. Stems up to 2 inches in diameter can be used (Sotir and Gray 1992). The basal end of the cuttings is always oriented in the same direction during collection and bundling. Cuttings for brush layers should be long enough that the growing tips are just exposed at the soil surface, while the basal portion of the cuttings reaches to the back of the bench (Sotir and Gray 1992). For rock gabions, rock walls, and crib walls, cuttings should be long enough to extend into soil or backfill behind the structures. During collection, cuttings are placed in bundles and secured with twine. Bundles should be light enough to carry. The optimum period to collect cuttings is during the dormant period when the plants have lost their leaves. If cuttings are collected outside of this period, then testing the viability of the cutting material is essential (Section 3.8.2, see Soil Structure). Fine branches dry out quickly if exposed to warm, dry temperatures. Cuttings should be protected during transportation, storage, and handling to avoid drying.

Storage—Refer to Section 5.4.3, see Live Stakes.

Installation—Branched cuttings are laid out on benches so the basal end of the cutting reaches to the back of the bench and the growing tips extend just beyond the front. Soil is placed over the cuttings and tamped to ensure there are no large air spaces. Excessive compaction is unnecessary for plant establishment and is often detrimental for long-term plant growth (Section 3.8.2, see Soil Structure). The material used to cover live branches in or behind crib walls, rock gabions, and rock walls is often low in water-holding capacity, nutrients, and organic matter. Soil amendments, such as compost, can be incorporated into backfill material to improve water-holding capacity and to serve as a long-term source of nutrients and organic matter. These amendments can increase establishment and improve plant growth (Section 5.2.5). Waiting until after the construction of crib walls, rock gabions, and rock walls to amend the soil is not practical or feasible.

Live Fascines

Live fascines are cuttings bound together to form a long continuous bundle (Figure 5-109). When installed on the contour, live fascines slow runoff, increase infiltration rate, capture sediments, reduce slope length, and revegetate the site (Sotir and Gray 1992). Live fascines have a good potential for quick establishment because of the high density of buds near the surface of the soil. Live fascines can quickly send out shoots and roots early in the growing season and become established before summer (Figure 5-109).

Fascines are used in the construction of live pole drains to drain saturated slopes, small slumps, or gullies (Polster 1997). Live pole drains are designed to intercept surface water from unstable slopes or seepage areas, and transmit it through a system of interconnecting bundles to more stable areas (Figure 3-70). The constant supply of intercepted water encourages vigorous growth of the cutting material into a continuous stand of vegetation. Fascines are also used as the base or support in the construction of modified brush layers. Live fascines have great potential for establishment because of the high density of buds just under the surface of the soil. These buds can emerge quickly in late winter and early spring. Because they are installed at the soil surface, live fascines are more prone to drying out than live brush layers or live stakes. For this reason, live fascines are more successful on moist sites or in conjunction with live brush layering or live staking.

Collection—Branches and stems up to 2 inches in diameter are collected from the wild or from stooling beds and gathered to form a long continuous bundle. Fascines vary in length from 5 to 30 feet, and from 6 to 8 inches in diameter. For large projects, construction of a series of sawhorse-type structures makes this operation easier and more efficient (Sotir and Gray 1992). At frequent intervals, bundles are secured with twine to hold the fascines together. Cuttings can be collected during the dormant season when the plants have lost their leaves. Fine branches dry out quickly if exposed to warm, dry temperatures and should be protected during transportation, storage, and handling

Storage—Refer to the discussion in Section 5.4.3, see Live Stakes.

Installation—Prior to installation, trenches can be created at the proper depth so the top of the fascine is flush to the surface of the slope when installed. The shape of the trench should allow soil contact with all portions of the bundle. Soil is tamped down around the sides of the bundles to ensure soil contact, and the upper fifth of the bundle is covered by a thin layer (<1 inch) of soil. A very small portion of the fascine should be exposed, but not enough to dry the stems. If the fascine is buried too deeply, vegetative growth will be restricted.

5.4.4 Installing Plants

Introduction

Although a wealth of information exists about planting for reforestation, very little information has been published about planting nursery stock on roadsides. Several references can be found discussing harsh site reclamation. Ashby and Vogel (1993) is an excellent source for planting on restored minelands.

Before beginning a planting project, the revegetation plan and plant production contract can be reviewed carefully, as should the Target Seedling Concept (Figure 5-110) which was considered during the planning process (Section 3.13.1). The first four steps were covered when plants were ordered during the planning process. The timing of the outplanting window and planting tools should be considered at this time.

Timing of the Outplanting Window—The outplanting window is the period in which environmental conditions on the outplanting site are most favorable for survival and growth of nursery stock (Figure 5-111). The outplanting window is usually defined by limiting factors, and soil moisture and temperature are frequent constraints. In most of the continental United States, nursery stock is outplanted during the rains of winter or early spring when soil moisture is high and evapotranspirational losses are low. Fall outplanting is another option on some projects, especially when dormant and hardy plants can be installed just before the normal rainy season begins. Planting during the summer is usually discouraged because the nursery stock is not dormant and will experience severe transplant shock. If nursery stock is carefully handled and plants can be irrigated, then summer plantings are possible.

Planting Tools and Techniques—Nursery stocktype and the conditions on each outplanting site should be considered before planting begins. All too often, planters develop a preference for a particular planting implement because it has worked well in the past. However, no one tool will work for all types of nursery plants and under all site conditions. Size of nursery stock, in particular the depth and width of the root plug, is the critical consideration. Tall pots, for example, have an unusually deep root plug, which makes them difficult to plant properly with standard tools. For some types of plants and, especially, for large planting projects, it may be necessary to buy or rent specialized equipment, that can be secured in advance. The planting tools recommended for roadside revegetation projects are discussed in Section 5.4.4, see Select Planting Tools and Methods.

Define Planting Areas

When construction is completed, the project site is assessed for planting. A detailed map showing the exact planting locations and conditions is developed by reviewing each location on the ground. Each area should be identified on a map and described in a spreadsheet by the following:

• Planting area acreage
• Planting patterns
• Plant spacing (density)
• Survival potential
• Species and stocktype mix

With this information, a planting strategy can be developed for each planting area using calculations similar to those shown in Figure 5-112.

Size of Planting Areas—The first step is to measure the area of each planting unit. Although they could be calculated from Project plans or acquired from the electronic files, the true planting areas should be measured on-site. A practical method is described in Figure 5-113.

Planting Patterns—The pattern at which nursery stock is planted is critical for creating a more natural and visually pleasing roadside experience. Most planters have learned to install plants at uniform spacing and in rows (Figure 5-114A). Although uniform patterns ensure that all plants have equal growing space, it is not natural. Planting seedlings in groups (Figure 5-114B) or clumps (Figure 5-114C) is more visually appealing and more ecologically functional. Maintenance or roadsides can be considered in the location and spacing of plants. The operational right of way will include an obstruction free run-off area or "clear zone" next to the roadway. This clear zone would allow a driver to recover from an off-pavement event with potentially no or minor damage to the vehicle. The clear zone will also be kept in such a manner that roadside vegetation does not provide cover to wildlife. The well designed planting pattern of vegetation beyond the clear zone will determine what maintenance practices are performed on this section of roadway and accommodate the required equipment's width and turning ability in the spacing and location of vegetation. Vegetation that benefits pollinators would include trees, shrubs and flowering forbs as well as native grasses. Plantings with all of these arranged in a foreground, middle-ground and back-ground design can be discussed with maintenance staff so that grasses and forbs that skirt the shrubs will be allowed to remain.

The revegetation specialist can meet with maintenance staff during the planning stage. Maintenance operations, especially mowing and herbicide use are significant reasons that limit roadsides as pollinator habitat. Mowing interrupts the life cycle of most wildflowers, preventing their blooming and subsequent reseeding, and over time effectively eliminating the plants from the roadside landscape. If the revegetation specialist is not able to agree on with maintenance personnel on practices that allow flowering plants to persist, then the expensive wildflower seeds can be removed from the proposed seed mix.

More specific considerations about planting patterns are based on project objectives and site characteristics. Topography and soil characteristics are two important site characteristics that can inform planting patterns. If one of the project objectives is to support wildlife, then topography can be used to design planting patterns that provide shelter (e.g., clumped trees at the bottom of a ravine) or migrations routes (e.g., trees planted as covering screens leading towards adjoining natural areas). Very sandy or serpentine soils may be avoided at a site and the spatial pattern of these soils will inform planting patters. A typical example would be to use plants to screen potentially unattractive areas, such as large cuts and fills or obliterated roads. Screen plantings can also be used to screen views of the roadway from adjacent properties. Plantings can frame and highlight attractive views. Locations of plants can be organized at intersections or points of interest to differentiate the location from the surrounding landscape. The potential to influence the road user's experience is very high. Long monotonous landscapes of homogenous plantings can lull a driver to sleep and can be an unsafe distraction. A roadside that provides variety in form, color and use of materials can enliven the driver's experience. Landscape architects and designers using the many principles of design can exploit opportunities that may not be evident to a botanist or engineer. A thorough site analysis incorporating views from the road alignment (both directions) and views toward the road from adjacent properties is important in determining of where trees or shrubs should be planted to create views or screen views as the situation demands.

Plant Spacing—The planting spacing or density will determine how quickly an area will become screened by vegetation. The higher the density, the more plants are required. Selecting the appropriate density can be based on the existing vegetation density recorded at reference sites, as well as both short- and long-term project objectives. It can also be based on the expected survival rates of the planted stock, because not all planted stock will survive.

Survival Potential—Each planting area can be assessed for its unique site characteristics, such as rock content, soil depth, accessibility, steep slopes, and poor accessibility. These will determine the stocktype and species selection, method of planting, and the difficulty of transporting large plants to the site. The identified site limitations will determine the expected survival rates; target survival rates should be at least 70 percent to minimize the costs of site preparation and anticipated replanting.

Species Mix and Stocktype—Each planting area will have a different mix of species and stocktypes based on the site characteristics and project objectives defined during the planning stages. This is a refinement of those plans based on a site-specific evaluation of the area. Trees and other large woody plants are considered "keystone species" because of their sheer size and longevity. These structurally and functionally dominant plants play a pivotal role in restoration plantings because they generate physical structure and create ecological niches for many other species. This fosters the in-seeding of other plants, resulting in a more natural and visually appealing landscape. In the selection of flowering forbs to provide habitat to pollinators a variety of species should be selected. Besides being regionally endemic, species can be selected that have flowering periods overlap so that, from early spring through late fall, at least one or more species is flowering to provide nectar and pollen to insects.

Select Planting Tools and Methods

One planting method will rarely work for all planting areas and all species in a revegetation project. Roadside sites offer some serious challenges to planting nursery stock, most notably highly compacted soils and often a high percentage of rock. Road projects create the opportunity for unique situations, such as planting islands.

The most common type of planting method is manual planting using a shovel. Recent developments in mechanized planting equipment have increased the tools available. The most common types of planting tools for roadside revegetation sites are described below.