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Chapter 4
Construction Practices for Environmental Stewardship
4.12. Establishing Vegetation at Construction Sites

When little topsoil is left in roadside environments after construction, mulches, water, lime, and/or fertilizers may be required in order to establish vegetation. A soil analysis can assist in identifying these additional requirements. A horticulturist and/or some landscape architects should be able to interpret the soil analysis. If outside the optimum planting seasons, a method of soil cover, other than vegetation, may be necessary. These include mulches and erosion control fabrics .

Some DOTs are undertaking research to identify what vegetation establishment methods work best in their states and ecoregions. Studies on compost usage are occurring in the west and mid-west, from Texas in the south to Idaho in the north. The Nebraska Department of Roads has research results due in late 2004, which will be used to develop technical guidelines for vegetation establishment on roadway shoulders. The project is examining the interaction effects of seed priming, type of mulch, and level of irrigation on soil movement and establishment of the short grass mixture on the foreslope of roadway shoulders; and the interaction effects of composted manure applications and a six to twelve inch compacted buffer strip between the paved shoulder and the seedbed on soil movement and establishment of the short grass mixture on the foreslope of the roadway. Delaware DOT will publish a vegetation management manual in 2005, in conjunction with the agency's tree preservation policy for a Livable Delaware. [N]

The following recommended practices to promote plant establishment during the construction stage have been culled from the best practices, manuals, bulletins, and research of lead DOTs in the field, and are summarized as follows:

Do not deviate from plans without approval of the Landscape Architect. Plans developed by the landscape architect will include plants most appropriate for the region and landform in which construction will be occurring, and will help ensure survival of intended vegetation and minimize the spread of noxious weeds.

Test seed for germination and to ensure that it is weed free.

Enforce seeding contract requirements. Utilize specs that allow withholding of funds. One way to enforce the requirements of the seeding contract is to withhold funds for incomplete grading and turf establishment on a per acre level. Mn/DOT Technical Memorandum Number 85-4-RD-1 allows for $700 to $2,000 per acre to be withheld from the contract when grading and turf establishment requirements are not met.

Use correct plant handling and planting techniques to facilitate plant establishment.

Keep the rootball moist and bare roots covered at all times.

When planting, the root flare should be 10 percent of the root ball depth above ground level.

Dig the planting hole so it is a minimum of 2 times the diameter of the rootball width. Larger holes will be required in more compacted soils.

Plants smaller than 20-gallon container size do not need to be staked.

Mulch should cover only the edge of the rootball. When planting is completed, there should be no additional soil and little or no mulch over the root ball for container plants.

Additional information on tree planting can be found on-line.

Follow transplanting guidelines, if applicable. The reason for setting transplant guidelines is to increase the likelihood of plants surviving, growing to maturity, and reproducing. The chance of success is much greater if plants from the same altitude and ecosystem are used because they are adapted to that area's climate and elevation. The following guidelines are recommended by the Washington State Department of Transportation. [N]

  • Collect plant materials during the dormant season.
  • Collect cuttings from 30 to 50 parent plants in good condition (if available). In general, take no more than 33 percent of the parent plant's material and take no more than 50 percent of cuttings or seed from a given area.
  • For plant cuttings, use young shoots (1 to 2 years old). Older and larger stems tend to have higher mortality.
  • Keep plants protected from wind and heat.
  • Plant materials the same day as collected when possible, ideally within about 2 hours of lifting. Keep plants moist and free from wind and heat exposure.
  • In some cases soaking cuttings for up to 5 days prior to planting enhances success. Protecting stems from wind and keeping them cool and moist is essential.
  • Planting holes should be deep enough so that the downslope side of the rootball is entirely buried.
  • Plant the plant so the root collar is at the depth at which it was previously growing.
  • Spread roots out so none are kinked or circling. Protect roots, especially fine root hairs on the main root system. Add water, if available, to reduce voids and increase root and soil contact.
  • Use on-site soil to backfill the hole. Firmly tamp the soil around the plant. Be careful not to compact the soil.

Transplanting a microsite: Depending on site conditions and project objectives, it might be preferable to salvage and transplant a small section of ground. This section usually contains several plants with roots, mycorrhizae, seed, soil, soil microorganisms, and duff materials. This technique provides great benefits to the area being revegetated. For transplanting small sections of ground, excavate an area large enough to "plant" the entire piece. Lay it in the excavated area and level with adjoining ground. Use excavated soil to secure edges of transplanted piece. Tap gently into place. Whenever possible, water the transplant.

Apply fertilizer in a manner and at application rates that will not result in loss of chemicals to stormwater runoff. Follow manufacturer's recommendations for application rates and procedures.

Make sure seed is covered with the correct depth of soil if broadcasting or hydroseeding. The depth will depend on the type of seed being used. Check with the HQ Horticulturist for correct planting depths for the seed mix. Composted organic amendments, in place of fertilizer, also work well. Some compost blowers are able to inject seed as the compost is blown onto the site.

When using either cuttings or rooted stock, ensure soil and the roots make good contact. This requires compaction of the soil, either by foot or by equipment, to avoid air pockets. It also requires that the soil be at the right moisture content. Another aspect to consider is that quite frequently after planting, the resulting soil is too rough and loose to support vigorous seed growth. The roughness promotes rapid drying, and the looseness yields poor seed-to-soil contact and also erratic planting depths where mechanical seed drills are used. As a result, some means of compaction should be employed to return the soil to an acceptable state for planting. Special problems may be encountered in arid or semiarid areas (Anderson et al. 1984). The salt content of the soil in these settings is critical and should be tested before planting. Deep tillage is advisable, with holes augured for saplings extended to the water table if at all possible. First-year irrigation is mandatory; ongoing fertilization and weeding will also improve survival.

After seeding, protect the site from additional surface water flow, specifically overland flow from roads. Direct the water flow away from the project area with gravel drains, swales, culverts, or drainpipe.

Use weed-free straw or wood cellulose fiber mulches to minimize rain splash erosion. When using straw as a mulch, use as thin a layer as possible to cover the soil (¼ inch). Grass seed cannot sprout if the mulch is too thick. Wood mulch may be chosen over other stabilization measures to reduce germination of noxious weeds and the need for vegetation control measures. Wood mulch should not be applied to steep slopes or placed into drainage paths that could receive concentrated flow. Wood mulch is prone to displacement under these conditions. Contact the District Landscape Specialist, District Erosion Control Specialist or Landscape Architect for the appropriate application rates and use the recommended application rate. Wood mulch may be applied by hand, with blowers or with chippers. Avoid application onto hardscaped areas. Mulch will require periodic inspection. [N]

 

4.12.1 Establishing Native Grasses and Forbs
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Although a well-chosen and established plant community should require no human assistance to maintain vigor and function, competition from other plants during establishment might be a problem. Competing plants commonly do not provide the same long-term benefits for stability, erosion control, wildlife habitat, or food supply. The restoration plan therefore must include some means to suppress or eliminate them during the first year or two after construction.

Mn/DOT has compiled a detailed set of recommendations for establishing native grasses and forbs, as summarized in this section. [N] Seeding native grasses and forbs (wildflowers) can be accomplished using a number of different methods; however, due to the complexity of seed sizes, textures and densities, care needs to be taken to ensure that the site is well prepared and that seed is placed properly. Older style drills may clog easily with fluffy seeds. Broadcast seeding and hydroseeding also work, natives should be seeded according to several general "rules of thumb," as recommended by Mn/DOT:

Prepare a firm seedbed, which is preferred by native seeds.

Large and/or fluffy seeds should be buried approximately 1/4 inch deep.

Seed should be lightly covered with soil. Harrowing or raking works well.

Small and/or fine seeds (most forbs) should be scattered over the soil surface.

Use diverse plantings, which are more resistant to drought, floods, and pathogens than monotypic or low diversity plantings, though care should be taken in selecting mixes to avoid unhelpful competition between species. The inclusion of a diverse mixture of forbs is greatly beneficial to wildlife and the forbs occupy niches that would otherwise be occupied by weeds. Native legumes also fix nitrogen, which is made available to other plants in the system through fungal interactions between plants. Cool-season native grasses tend to establish quickly and will decrease over time on sites where warm-season species would normally dominate. Warm-season native grasses tend to be slower to establish, but are extremely hardy and long-lived. Warm-season grasses also tend to stay standing over the winter and provide the best snow filtering capabilities and wildlife habitat.

Caltrans underwrote a number of experiments to study the competitive interactions between herbaceous species used in erosion control seedings and whether species that use resources differently in space and time create more stable plant communities than species with more similar resource use patterns. [N] The results of these experiments suggest that within an herbaceous plant community, species have the potential to partition their resources, which may allow them to co-exist without competitively excluding one another. Caltrans' researchers found that mixtures including species with different spatial and temporal resource use patterns utilized soil water more completely and produced greater and more consistent aboveground biomass than mixtures of species with more similar resource use patterns. More species rich mixtures used soil water more completely and produced more aboveground biomass with more stable species composition than less diverse mixtures. Invaders performed worst in mixtures that included species with resource use patterns similar to the invader. The researchers also reported results from a survey of erosion control plantings and relict perennial grass communities. Annual precipitation and geographic location were the environmental variables that best explained the species composition data. Relict perennial grass stands had greater mineralizable and total nitrogen levels, higher perennial grass cover, and lower legume cover than revegetation sites. Soil depth was identified as an important factor in success of revegetation seedings [N] but was not measured. [N]

Consider cover/nurse crops. Cover crops provide a quick short-term vegetative cover while the permanent native species are establishing. A cover crop reduces the soils erosion potential and moderates the native seedlings microclimate during establishment. Typical cover crops in Mn/DOT's native mixes include oats/winter wheat, annual rye grass and slender wheatgrass. Winter wheat is substituted for oats during fall plantings. The annual rye grass provides good cover in early spring but does not do well in late spring and summer. It also does well dormant seeded. However, Caltrans researchers suggested that the use of non-biological means of erosion control (e.g. straw mulch, mats or wetting agents) with native perennial grasses may be preferable to including fasting growing species. Physical erosion control methods in combination with planting perennial grasses, forbs and shrubs, may optimize erosion control by shielding the soil from the impacts of rain and run-off in the short term and establishing stable plant communities with dense and deep root systems for long term soil protection. [N]

Mulching or temporary erosion control. It is recommended to protect a new seeding by covering it with mulch or an erosion control blanket. In general, slopes that are 1:3 (vertical: horizontal) and flatter should be mulched with a clean grain straw or native grass mulch and disc anchored following seeding. Mulching should attempt to achieve 90 percent coverage of the exposed soil surface. This generally requires about 2 tons per acre of straw mulch. It is also recommended to use a high quality, certified weed free mulch. On slopes that are steeper than 1:3 it is recommended that the seeding be covered with an erosion control blanket. Generally, straw blankets containing double netting (Straw 2S) perform best with native plantings. If seeding is being done in a ditch or swale that will receive moderate water flows for periods of time, it is recommended that a straw/coconut blanket be used to cover it. Other more severe situations such as very steep slopes and/or channels exposed to high water velocities will require more specialized treatments that are not covered in this manual.

Fertilizer: It is always recommended to take soil tests to determine the existing soil fertility in order to choose an appropriate fertilizer based on the soil deficiencies. It is also recommended to choose a slow release fertilizer with 80 percent Water Insoluble Nitrogen (WIN) and 0 percent chlorides. If a generic fertilizer is used, a 10-10-20 NPK analysis is recommended. A general rule of thumb is that native grasses and forbs require about 50 percent less Nitrogen and 25 percent more Potassium than turf and forage species.

Seeding Into Agricultural Fields: Many fields that have been row cropped will have some amount of herbicide residue present, depending on what the crop was and what type of herbicide was used on the site to control weeds. Leaving the site fallow, or planting a temporary cover for a season before planting, will help reduce herbicide residue. Also be aware that herbicides used to control annual grasses may adversely affect native grasses being planted and broad-leaved herbicides may adversely affect forbs being planted.

Seed Treatments: Be aware that seeds of many native species require specialized treatments such as cold/moist stratification, scarification, etc. Many of these species go through such treatments naturally if seeded in the fall.

Origin Requirements: It is preferred that seed of all native grasses and forbs be "certified" to be of local, state, or regional origin and of wild ecotype. Some plant materials can be obtained from commercial sources, but many will need to be collected. When attempting to restore native plant communities, it is desirable to use appropriate genotypes. This requires the collection of seeds and plants from local sources. Early contact with selected sources of rooted stock and seed can ensure that appropriate species in adequate quantities will be available when needed.

Collecting Salvageable Plants On -Site or at a Donor Site: The site itself might also be a good source of salvageable plants. Live cuttings can be collected from healthy native vegetation at the donor site. Sharp, clean equipment should be used to harvest the plant material. Vegetation is normally cut at a 40 to 50 degree angle using loppers, pruners, or saws. If the whole plant is being used, the cut is made about 10 inches above the ground, which encourages rapid regeneration in most species. Cuttings typically range from 0.4 to 2 inches in diameter and 2 to 7 feet long.

Transport and Storage of Plant Materials: The requirements for the transport and storage of plant materials vary, depending on the type of material being used. Depending on species, seeds may require a minimum period of dormancy of several weeks or months, with specific temperature requirements during that time. Some seeds may also require scarifying or other special treatment. Nurseries that specialize in native plants are recommended because they should be cognizant of any special requirements. Although the necessary information for any chosen species should be readily available from local seed sources or agricultural extension offices, this interval should be recognized and accounted for in the overall implementation schedule. Live cuttings present rather severe limitations on holding time. In most cases, they should be installed on the day they are harvested, unless refrigerated storage areas are secured. Thus, donor sites should be close to the restoration site, and access and transportation should be orchestrated to coincide with the correct stage of construction. Live cuttings should be tied in manageable bundles, with the cut ends all lying in the same direction. Since drying is the major threat to survival at this stage, cuttings should be covered with damp burlap during transport and storage. They should always be shaded from direct sun. On days with low humidity and temperatures above 60 degrees Fahrenheit, the need for care and speed is particularly great. Where temperatures are below this level, "day-after" installation is acceptable, although not optimal. Any greater delay in installation will require refrigeration, reliably cold weather on site, or storage in water. Rooted stock is also prone to drying, particularly if pots or burlap-wrapped roots are exposed to direct sun. Submergence of the roots in water is not recommended for long periods, but 1 to 2 hours of immersion immediately prior to planting is a common practice to ensure the plant begins its in-place growth without a moisture deficit. Onsite storage areas should be chosen with ample shade for pots. Bare-rooted or burlap-wrapped stock should be heeled into damp ground or mulch while awaiting final installation.

Timing. The optimum conditions for successful plant installations are broad and vary from region to region. As a general rule, temperature, moisture, and sunlight must be adequate for germination and establishment. In the eastern and Midwestern United States, these conditions are met beginning in late winter or early spring, after ground thawing, and continuing through mid-autumn. In the West, the typical summertime dryness normally limits successful seedings to late summer or early autumn. Where arid conditions persist through most of the year, plants and seedings must take advantage of whatever rainfall occurs, typically in late autumn or winter, or supplemental irrigation should be provided. Because the requirements can vary so much for different species, the local supplier or a comprehensive reference text [N] [N] [N] [N] should be consulted early in the restoration design phase. If rooted stock is to be propagated from seed before it is planted at the restoration site, 1 to 2 years (including seed-collection time) should be allowed. Plants should be installed when dormant for the highest rate of survival. Survival is further influenced by species used and how well they are matched to site conditions, available moisture, and time of installation. In mild climates, the growth of roots occurs throughout the winter, improving survival of fall plantings. Where high wintertime flows are anticipated, however, first-season cuttings might not survive unless given some physical protection from scour. Alternatively, planting can occur in the spring before dormancy ends, but supplemental irrigation might be needed even in areas of abundant summertime rainfall. Irrigation might be necessary in some regions of the country to ensure successful establishment of vegetation. [N]

Interestingly, recent MoDOT research found that seed to soil contact was a critical issue in seeding, and exceeded use of native species and less than ideal timing of plantings in producing desirable germination rates. MoDOT found a 275 percent increase in the number of plants simply by rolling an area after seeding and garnered the best results by drilling the seed and rolling the area resulting in a 360 percent increase over broadcast and dragging an area. Consequently, MoDOT is revising construction requirements such that all areas of a construction project that are to be seeded and are less than or equal to 3:1 slope will have the seed placed at 1/4" depth with a drill specifically designed for native grasses, that allow for the handling of large fluffy seed and also smaller seed. The area will then be rolled prior to the application of any mulch. All other areas greater than 3:1 will have the seed placed either by broadcasting or hydraulic seeding with the area tracked with a dozer prior to the application of any mulch material to produce better seed to soil contact than seed placed loosely on the top of the soil. [N]

 

4.12.2 Inspection of Nursery Stock
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An inspection of planting stock should be made at the nursery or other approved source to ensure the quality of planting stock. Someone with horticultural expertise should accomplish the inspection. [N]

  • Judgment should be exercised and allowances made for reasonable variation in growth and appearance. The size and quality of planting stock cannot be rigidly standardized because of varying growing conditions.
  • All planting stock should be of the genus, species, variety, and sizes specified and shall conform to the Contract
  • Specifications for the particular species, or variety, regarding straightness of trunk, branching structure, proportion, health, and size of material.
  • Individual plants should be measured to determine conformance with contract.

Inspection at the nursery or other source of supply should include: [N]

  1. Check the general condition of the plant in the block from which the stock is to be taken for:
    1. Uniformity of Leaf Coloration. Plants that exhibit yellowing or discoloration could indicate poor drainage, fertilizer deficiency, herbicide damage, insect damage, or disease, and may not meet specifications.
    2. Bud Development. During dormant periods of the growth cycle plants should have buds that are firm, moist and uniformly spaced. A slight cut may be made into the bark to determine that the cambium (growing layer just beneath the bark) is moist and green.
    3. Uniformity of Growth. The plants in any given block should exhibit uniform vigor and health. Plants that do not conform may not be acceptable.
    4. Spacing of Plants in the Row. Vigorous growing, well rounded, fully developed plants will transplant well. Quality nursery stock should be grown with sufficient spacing to permit good development of the individual plant. Plants grown too close together may be extremely high headed.
    5. Presence of Weeds. An overgrown, weed-infested nursery block indicates lack of care and the plants growing in it may be in a poor state of vigor because of the weed competition. Weeds should not be growing in containers.
  2. Check individual plants for freedom of defects such as:
    1. Decay. On trees, look for spots of decayed tissue on the trunk and branches.
    2. Sun Scald or Sunburn. The destruction of tissue caused by the sunrays striking a plant on the south or southwest side. This may result in the death of cambium tissue and bark, exposing the plant to secondary insect and/or disease infestation.
    3. Abrasions of the Bark. Abrasions severe enough to damage the cambium tissue may be sufficient for rejection.
    4. Girdling Roots. Roots that grow around another root or a stem, thus tending to strangle the plant.
    5. Improper Pruning. Stubs resulting from improper pruning, which have died back, are an excellent point of entry for disease organisms. All cuts should be flush with the trunk or supporting branch. When a cut is made to encourage branching, it should be made back to a bud.
    6. Frost Cracks. Long vertical splits in the bark and/or wood may occur on the south and southwest sides of young and thin barked trees. Such cracks may become invaded by canker or decay producing fungi and bacteria.
    7. Signs of Injury. Dead leaves; dry buds; dieback of twigs and branches; blackened sapwood and sunken, discolored patches of bark (sun scald) on the trunk or limbs.
    8. Root Ball. Roots should be all through the container so the root ball stays together during planting.
  3. Check individual plants for freedom from plant diseases and pests such as:
    1. Diseases. These will appear in a variety of forms such as abnormal growth of collar, leaves, twigs, fruits, discoloration of leaves and bark, unusual discharges of sap through the bark, etc. Any plant showing evidence of disease should be rejected.
    2. Insects. Look for insect eggs, spider webs or evidence of damage from insect feeding on leaves, twigs, buds, or other plant parts. Examine the trunks of trees for borer holes that appear as tunnels drilled into the bark and inward into the wood of the trunk. Trees with evidence of borers or other insect damage should be rejected.
  4. Check individual plants for proper habit of growth as follows:
    1. If a particular habit, i.e., single stem, multiple stem, etc., has been specified, be sure to obtain plants that conform to this requirement.
    2. If no particular growth habit has been specified, then the current state Nursery Association Grower's Committee Recommended Tree Specifications as published by the AAN should be used as a guide.
    3. Shade and flowering trees should have top growth symmetrically balanced. Shade trees should have a single leader. The balancing should be well developed and characteristic of the species.
    4. Evergreen trees should be full foliage plants with uniform density. Sheared plants, such as pines sheared for Christmas trees, should be avoided unless specified.
    5. Shrubs should be well branched in a manner characteristic of the species. The current American Standard for Nursery Stock Z60.1, is an excellent guide for determining the proper number of branches for certain size shrubs.
  5. Check all container grown plants to determine that they meet the requirements outlined in 1 through 4, above. In addition, a random sampling of plants should be removed from their containers to determine that the root system is healthy. Plants that are found to be pot bound and plants that have insufficiently developed root systems to hold the soil together when removed from the container should be rejected. Healthy roots should be able to hold the soil mass together yet not be crowded around the outside perimeter of the container.
  6. Planting stock that is based on the above criteria may be tagged with seals placed on all plants or representative samples at the nursery. This will assist in future inspection of these plants when delivered on the job site. Seals placed on planting stock for later identification do not imply acceptance on the construction site.

 

4.12.3 Seed Selection and Specification
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Select species that should be on the project site. A number of state DOTs have developed native plant mixes and selection guidelines and maps. Check with the landscape architect to see what is used in your state. As availability is a factor in seed selection, there is a natural reaction to use whatever is readily available from seed companies and native plant nurseries and try and make them work on the project. Also, there are few ways to determine what originally grew on site and what percentage of each species formed the mosaic of the original ecosystem, if the natural ecosystems are not present today. Native seeds are often not available in bulk quantities, leading project managers to the next question of where can they go for the proper genetic material.

Determine whether sufficient quantities of local native seeds are available. If sufficient quantities are not available, seed samples can be collected and cultivated in bulk with a year lead time. Local seed collection of the native plant ecotypes in sufficient quantities for a project can be conducted in areas where there are still large native stands. The few pounds of seed that could be hand-collected for a project can be turned over to a grower to grow under contract bulk quantities. One pound of hand-harvested native grass seed, if put into commercial cultivation can yield 100 pounds of commercially-grown seed within 12 months. Aim to have 50-100 pounds of native seeds available for each acre that will be restored, so the exotic seedbank already in place can be overwhelmed. Calculate for 50 pounds per acre for pure-live-seed and 100 pounds per acre if it is 50-70 percent pure seed. Also be sure that the native seeds are weed, noxious weed, and "other crop" free. [N] [N]

Conduct many tiny test pilots (TTPs) to avoid tests and potential failure of large scale plantings, each the size of a few square yards (1-2 square meters), where a broad range of sowing rates, fertilizer rates, mulches, different sowing methods, soil preparation methods, etc. are tested. Within a very short time it will be obvious which TTPs have successful results, and then those results can then be used to plant on a larger scale. Two years of test plots are ideal, with the second year of TTPs used to make the 2-10 percent of successes to work better, and achieve close to 100 percent. This approach avoids weed control in the future. When the first acre is successfully completed, the local seed materials should then be in sufficient quantity to do a larger area, and efficient techniques developed to get the per-acre price down to a reasonable cost. S tart with a smaller area to test technologies and gradually ramp them up into larger areas. [N] [N]

Preserve native seedbanks and ecosystems throughout the state, to provide both models to work towards and in-situ seed resources. Caltrans, for example, has identified 20 Botanical Management Areas throughout the State and will continue to expand this list. These environmentally-significant areas exist along the state highway right-of-way and are remnants of California's native landscape. Sites are chosen for their biological integrity, species diversity, need for resource protection, and suitability for scientific evaluation, among other criteria. Caltrans and partners conduct an analysis of the best potential local natives, ecotypes, and methods of stabilization which can control erosion and prevent slides. The sites can also be used as seedbanks. Ideally native seedbanks would exist every 10 miles.

Buy quality seed, which is a critical component to success. The ideal method to assure quality is to specify "certified" seed. Certified seed must meet certain standards for germination and purity, and certification provides some assurance of genetic quality. Some native seed species are not available as certified seed; however, seed quality may be ascertained by examining percent germination and percent purity. Determine the true cost of seed by multiplying percent germination by the percent purity, which equals Pure Live Seed (PLS). Then multiply PLS by the price per pound. These calculations can increase the accuracy of bid comparisons. See must also be free of noxious weeds, which is noted on seed tags along with germination and purity. [N]

 

4.12.4 Seeding Methods, Considering Texture and Size
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When using seeds, planting should be preceded by elimination of competing plants and by preparation of the seedbed. [N] The most common methods of seeding in a restoration setting are hand broadcasting and hydroseeding.

If a drill or drop seeder is used, the seed mixture ingredients should be ordered such that the seed is packaged separately based seed size and texture. Fluffy seed should be placed in the native seed box that contains picker fingers. Fine seed should be placed in the fine seed box. Cereal grains, such as oats and winter wheat, used for a cover crop should be placed in the grain seed box that contains flutes.

If a broadcast seeder is used, the seed mixture may either be ordered mixed or as separate ingredients. During installation, the operator should be aware that fluffy seed will have a tendency to bridge or "ball up" in the seeder. Fine seed has a tendency to "pour through" the seeder. Therefore, an effective agitator is required in the seed box. Mixing heavier seed such as sideoats grama, wheat and oats will also help "weigh down" the lighter fluffy seed. If a hydroseeder is used, the seed is usually ordered as a mixture. The hydroseeder has a vigorous agitator in the tank.

Drop, Drill, and Broadcast Seeding Methods

Drop Seeding Onto Tilled Sites

This is the "standard" method for seeding native species on prepared sites such as those on construction projects.

Site Preparation - The site should be prepared by loosening topsoil to a minimum depth of 3 inches.

Fertilizer - If not basing the fertilizer application on soil test results, the fertilizer used should be a commercial grade slow release complete fertilizer applied at a rate of 400 lbs/acre at the time of preparing the seed bed for seeding. The fertilizer should contain 10-10-20 (NPK) analysis, and should include sulfur and iron as well (not less than 1 percent and not more than 8 percent added sulfur and iron).

Seed Installation - Seed should be installed with a drop seeder that will accurately meter the types of seed to be planted and keep all seeds uniformly mixed during planting (Trillion-type). The seeder should contain a minimum of three seed boxes; a fine seed box, a box for large/fluffy seeds, and a box for cool season or grains. It should be equipped with drop tubes and a packer assembly to compact the soil directly over the seed. All seeding should be done at a right angle to surface drainage.

Seeding Rates - Rates are specified in the mixture tabulation for the specified mix.

Harrowing - The site should be lightly harrowed or raked following seeding if the seeder does not contain a cultipacker.

Packing - Cultiacking the site following harrowing is recommended to ensure a firm seed bed.

Mulch - The site should be mulched and disc-anchored following packing.

Drill Seeding Into Temporary Cover Crops

This method involves two separate seeding operations. First, a temporary cover crop is planted on the entire site to stabilize the soil and control erosion. Second, the native seed mixture is installed the following fall or the next spring (during one of the optimum seeding dates) using either an interseeder type drill or by lightly disking down the temporary cover and seeding into it. The interseed method greatly reduces the erosion potential and reduces soil disturbance. Using this method allows for some early weed control before the native mixture is installed. This method is used for various reasons such as when a site is ready for seeding at a time of year that is not optimum for seeding a permanent seed mixture, the soils need to be stabilized rapidly for erosion control, or a field needs to be left fallow due to residual herbicide.

Establishment of Temporary Cover Crop

Site Preparation - The new site should be prepared for the temporary seeding by loosening topsoil to a minimum depth of 3 inches.

Fertilizer - The fertilizer used should be a commercial grade of slow release complete fertilizer applied at a rate of 200 lbs/acre at the time of preparing the seed bed for seeding. The fertilizer should contain 10-10-20 (NPK) analysis, and should include sulfur and iron as well (not less than 1 percent and not more than 8 percent added sulfur and iron).

Seed Installation - Temporary cover crops of oats, winter wheat, ReGreen or combinations of the above may be installed using a standard grain drill or broadcast. Planting depth should be 1/4 to 1/2 inch.

Seeding Rates - The temporary cover crop of oats or winter wheat should be seeded at a rate of 80 lbs/acre. If ReGreen is used as a cover crop, it should be installed at a rate of 30 lbs/acre.

Harrowing - The site should be harrowed or raked following installation of the temporary cover crop.

Packing - Packing is not required after installing the temporary cover crop.

Mulch - The site should be mulched and disc-anchored following packing.

Establishment of the Native Mixture

The native mixture can be established into the areas previously seeded with a temporary cover crop by one of two methods; 1) interseeding using a no-till drill, or 2) by lightly tilling the area with a disc and seeding using one of the other acceptable seeding methods.

Site Preparation for Interseeding - No tillage is necessary for installation of the native seed mixture. The site may require mowing if the temporary cover has grown taller than 12 inches and is still actively growing (winter wheat may require this). This will stop the rapidly growing cover crop from reaching maturity and shading out the establishing native vegetation. Optimal height for existing vegetation to be drilled into is 4-6 inches. No other site preparation is necessary.

Site Preparation with Light Tillage - The area seeded with a temporary cover crop should be prepared by lightly disking to incorporate some of the mulch and temporary cover crop into the soil surface. Approximately 50 percent of the soil surface should be visible through the mulch or plant debris. Much of the existing cover should be left in place for its mulch value.

Fertilizer - The fertilizer used should be a commercial grade of slow release complete fertilizer applied at a rate of 200 lbs/acre at the time of preparing the seed bed for seeding. The fertilizer should contain 10-10-20 (NPK) analysis, and should include sulfur and iron as well (not less than 1 percent and not more than 8 percent added sulfur and iron). The rate is reduced by half the normal recommendation because the initial half of the fertilizer was applied with the cover crop.

Seed Installation By Interseeding - The native seed mixture should be installed with a seed drill that will accurately meter the types of seed to be planted and keep all seeds uniformly mixed during the drilling (Truax-type). The drill should contain a minimum of two seed boxes; a fine seed box and a box for large/fluffy seeds, and it should be equipped with disc furrow openers and packer assembly to compact the soil directly over the drill rows. Maximum row spacing should be 8 inches. The inter-seeder drill should be out-fitted with trash rippers which will slice through the vegetative mat and make a furrow into the underlying soil approximately 1 inch wide by 1/2 to 1 inch deep. These furrows should be directly in line with the drill seed disc openers. Fine seed can be drop-seeded onto the ground surface from the fine seed box, and large/fluffy seed should be placed to obtain a final planting depth of 1/4 to 1/2 inch. All drill seeding should be done at a right angle to surface drainage.

Seed Installation by Drilling Lightly Tilled Sites - The native mixture should be installed with a seed drill that will accurately meter the types of seed to be planted and keep all seeds uniformly mixed during the drilling (Truax-type). The drill should contain a minimum of two seed boxes; a fine seed box and a box for large/fluffy seeds, and it should be equipped with disc furrow openers and packer assembly to compact the soil directly over the drill rows. Maximum row spacing should be 8 inches. Fine seed should be drop-seeded onto the ground surface from the fine seed box, and large/fluffy seed should be placed to obtain a final planting depth of 1/4 to 1/2 inch. All drill seeding should be done at a right angle to surface drainage.

Seeding Rates - Rates are specified in the mixture tabulation for the specified mix. When using the 300 series mixtures, reduce the cover crop component from 70 lbs/acre to 35 lbs/acre.

Harrowing - Harrowing is not necessary when seeding the native mixture.

Packing - Packing the site is recommended to ensure a firm seed bed.

Mulch - Mulch may not be required with installation of the native mixture, depending on existing site conditions. The site should be mulched to achieve 90 percent ground coverage (10 percent bare ground). If this condition already exists mulch is not required.

Drill Seeding Into Existing Vegetation

This method entails killing the existing vegetation with herbicide and using an interseeder drill to install the seed.

Site Preparation - The site should be prepared by mowing existing vegetation to a height of 4-6 inches in spring or in late August/early September. The grass should be allowed to re-grow or "flush" before herbicide application with glyphosate, this may take 1-3 weeks depending on weather conditions. Addition of a surfactant and/or addition of 2,4-D to the mix often results in a more complete kill, especially with unwanted broad-leaved species. Recommended herbicide rates are 2.0 quarts/acre of glyphosate and 1.0 - 2.0 quarts/acre 2,4-D. Fall site preparation to control smooth brome grass may require higher glyphosate rates. Seeding can be performed 7-10 days after herbicide application. NOTE: Sites that contain significant weed infestations may require other types of weed control during preparation to ensure that the planting is a success.

Fertilizer - Fertilizer is generally not required when using this seeding method.

Seed Installation - The native seed mixture should be installed with a seed drill that will accurately meter the types of seed to be planted and keep all seeds uniformly mixed during the drilling (Truax-type). The drill should contain a minimum of two seed boxes; a fine seed box and a box for large/fluffy seeds, and it should be equipped with disc furrow openers and packer assembly to compact the soil directly over the drill rows. Maximum row spacing should be 8 inches. The inter-seeder drill should be out-fitted with trash rippers which will slice through the vegetative mat and make a furrow into the underlying soil approximately 1 inch wide by 1/2 to 1 inch deep. These furrows should be directly in line with the drill seed disc openers. Fine seed should be drop-seeded onto the ground surface from the fine seed box, and large/fluffy seed should be placed to obtain a final planting depth of 1/4 to 1/2 inch. All drill seeding should be done at a right angle to surface drainage.

Seeding Rates - Rates are specified in the mixture tabulation for the specified mix.

Harrowing - Harrowing is not required when using this seeding method.

Packing - Packing the site is recommended to ensure a firm seed bed.

Mulch - Mulch is not required when using this seeding method.

Broadcast Seeding

Broadcast seeding is performed either with mechanical "cyclone" seeders, by hand seeding or by any other method that scatters seed over the bare soil surface. The most desirable aspect of broadcast seeding is that there is no row effect such as that which results from drill seeding. This lends a more natural appearance to the planting. However, broadcast seeding may not be desirable if the weather is hot and dry and/or the soil moisture is content is low. It is essential that steps be taken to ensure good seed to soil contact when broadcast seeding is used.

Site Preparation - The site should be prepared by loosening topsoil to a minimum depth of 3 inches. It is critical that the seed bed be loosened to a point that there are spaces for seed to filter into cracks etc., otherwise it may end up on the surface and wash away with the first heavy rain.

Fertilizer - If used, the fertilizer used should be a commercial grade of slow release complete fertilizer applied at a rate of 400 lbs/acre at the time of preparing the seed bed for seeding. The fertilizer should contain 10-10-20 (NPK) analysis, and should include sulfur and iron as well (not less than 1 percent and not more than 8 percent added sulfur and iron).

Seed Installation - Seed should be installed by broadcasting it evenly over the entire site. Several types and sizes of broadcast seeders are available for use, ranging from fertilizer-type spreaders to power spreaders mounted on all terrain vehicles. Seed should be mixed thoroughly prior to seeding and should be mixed occasionally in the spreader to prevent separation and settling.

Seeding Rates - Rates are specified in the mixture tabulation for the specified mix.

Harrowing - The site should be harrowed or raked following seeding.

Packing - The site should be packed using a culti-packer or equivalent following harrowing.

Mulch - The site should be mulched and disc-anchored following packing.

Hydroseeding

Hydroseeding is an acceptable method for establishing natives when it is done correctly. However, it is imperative that the site is prepared and finished properly. Mn/DOT generally uses hydroseeding on steep slopes or other areas inaccessible to a seed drill such as wetland edges and ponds. Hydro-seeding native grasses and forbs is not recommended if the extended weather patterns are hot and dry and the soil surface is dry and dusty. The seed-water mixture should be applied within one hour after the seed is added to the hydro-seeder tank.

Site Preparation - The site should be prepared by loosening topsoil to a minimum depth of 3 inches. It is critical that the seedbed be loosened to a point that there are a lot of spaces for seed to filter into cracks etc., otherwise it may end up on the surface and wash away with the first heavy rain.

Fertilizer - If used, the fertilizer used should be a commercial grade of slow release complete fertilizer applied at a rate of 400 lbs/acre at the time of preparing the seed bed for seeding. The fertilizer should contain 10-10-20 (NPK) analysis, and should include sulfur and iron as well (not less than 1 percent and not more than 8 percent added sulfur and iron).

Seed Installation - Seed should be installed by hydro-seeding it evenly over the entire site. A fan-type nozzle should be used with approximately 500 gallons of water per acre. It is recommended to add approximately 75 pounds of hydromulch per 500 gallons of water for a visual tracer to ensure uniform coverage.

Seeding Rates - Rates are specified in the mixture tabulation for the specified mix.

Harrowing - The site should be harrowed or raked following seeding.

Packing - The site should be packed using a culti-packer or equivalent following harrowing.

Mulch - The site should be mulched and disc-anchored following packing.

NOTE: When seeding in conjunction with a hydraulic soil stabilizer (bonded fiber matrixes (BFMs), hydro-mulches, etc., it is recommended that a two-step operation be used. Seed should be placed first and the hydraulic soil stabilizer be sprayed on afterwards. This is to ensure that seed comes into direct contact with the soil.

 

4.12.5 Mulches
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Mulching limits surface erosion, suppresses weeds, retains soil moisture, and can add some organic material to the soil following decomposition. A variety of mulches are available with different benefits and limitations. Organic mulches, particularly those based on wood (chips or sawdust), have a high nitrogen demand because of the chemical reactions of decomposition. If nitrogen is not supplied by fertilizers, it will be extracted from the soil, which can have detrimental effects on the vegetation that is mulched. Certain species of wood, such as redwood and cedar, are toxic to certain species of seedlings and should not be used for mulch. Straw is a common mulch applied on construction and revegetation sites because it is inexpensive, available, and effective for erosion control. Appropriate application rates range from about 3,000 to 8,000 lb/acre. Straw can be spread by hand or broadcast by machine, although uniform application is difficult in windy conditions. Straw must be anchored for the same reason: it is easily transported by wind. It can be punched or crimped into the soil mechanically, which is rapid and inexpensive, but requires high application rates. It can be covered with jute or plastic netting, or it can be covered with a sprayed tackifier (usually asphalt emulsion at rates of about 400 gal/acre). Straw or hay can also be a source of un- desirable weed seed and should be inspected prior to application. Wood fibers provide the primary mechanical protection in hydraulic mulches (usually applied during hydroseeding). Rates of 1 to 1.5 tons/acre are most effective. They can also be applied as the tackifier over straw at about one-third the above rate. Hydraulic mulches are adequate, but not as effective as straw, for controlling erosion in most settings. However, they can be applied on slopes steeper than 2:1, at distances of 100 feet or more, and in the wind. On typical earthmoving and construction projects, they are favored because of the speed at which they can be applied and the appearance of the resulting slope - tidy, smooth, and faintly green. The potential drawbacks - introducing fertilizers and foreign grasses that are frequently mixed into hydraulic mulches - should be carefully evaluated. An appropriate mulch in many restoration settings is a combination of straw and organic netting, such as jute or coconut fibers. It is the most costly of the commonly used systems, but erosion control and moisture retention are highly effective, and the problems with undesirable seeds and excess fertilizers are reduced. The value of an effective mulch to the final success of an initiative is generally well in excess of its cost, even when the most expensive treatment is used. [N]

Chipped wood Readily available; inexpensive; judged attractive by most High nitrogen demand; may inhibit seedlings; may float offsite in surface runoff

Rock May be locally available and inexpensive Can inhibit plant growth; adds no nutrients; suppresses diverse plant community; high cost where locally unsuitable or unavailable

Straw or hay Available and inexpensive; may add undesirable seeds; May need anchoring; may include undesirable seeds

Hydraulic mulches Blankets soil rapidly and inexpensively; Provides only shallow-rooted grasses, but may out compete woody vegetation

Fabric mats Relatively (organic) or very (inorganic) durable; works on steep slopes; High costs; suppresses most plant growth; inorganic materials harmful to wildlife

Commercial compost Excellent soil amendment at moderate cost; Limited erosion-control effectiveness; expensive over large areas

 

4.12.6 Fertilizer
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Applications of fertilizer at the time of seeding are usually necessary. Most commercial fertilizers meet minimum standards, and quality problems are seldom encountered.

Ensure dry storage and shipment. If problems arise with fertilizers, they can usually be traced to the product becoming wet during storage or shipment.

If possible, apply fertilizer at the same time or prior to seeding, because once the seed has been applied, no additional traffic should be allowed on the site.

20-20-10 fertilizer can be used unless specific site conditions require different proportions. The numbers are percentages of three elements: nitrogen, phosphorus, and potassium, respectively. Therefore, 20-20-10 fertilizer contains 20 percent nitrogen, 20 percent phosphorus, and 10 percent potassium by weight.

Native or otherwise adapted species usually do not require the use of lime or agents to acidify the soils and fewer soil amendments (compost, etc.) may be necessary.

 

4.12.7 Irrigation
 

In any restoration that involves replanting, the need for irrigation should be carefully evaluated. Irrigation might not be needed in wetland and near-stream riparian sites or where rainfall is well distributed throughout the year. Irrigation may be essential to ensure success on upland sites, in riparian zones where seasonal construction periods limit installation to dry months, or where a wet-weather planting may have to endure a first-year drought. Initial costs are lowest with a simple overhead spraying system. Spray systems, however, have inefficient water delivery and have heightened potential for vandalism. Drip-irrigation systems are therefore more suitable at many sites. [N] There is also a greater potential for undesirable species with spray irrigation since the area between individual plants receives moisture.

The irrigation system establishment testing that is done within one week prior to the landscaping establishment inspection involves walking the project and checking the pressure regulating valves with a pressure gauge. [N]

  • The pressure gauge at the backflow prevention unit should be read and recorded with the other readings.
    • Changes in pressure should be investigated.
    • The backflow unit should be tested as required by a qualified representative.
    • Inspect filters and flush end caps, if necessary.
  • The establishment period for the irrigation system coincides with the landscaping establishment. The monthly inspections of the landscape establishment and the irrigation system establishment are done simultaneously.
    • During the regular monthly inspections, be aware of eroded areas or unusual wet spots.
    • Check the wetting pattern around each plant.

Arizona DOT also requires the Contractor to conduct a training and orientation session for State personnel covering the operation, adjustment, and maintenance of the irrigation system. The Resident Engineer arranges to have the maintenance, or local government personnel who will be involved with the irrigation system attend this orientation session. The as-built plans are made available so they can be reviewed and all features explained. One copy of the as-built plans are made available to the maintenance personnel when completed, along with parts lists and service manuals for all equipment.

 

4.12.8 Vegetation Establishment on Steep Cut Slopes
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Steep cut slopes present a unique challenge to successful re-vegetation of highway corridors following disturbances. The steepness of the cut slopes prevents practical replacement of salvaged topsoil with conventional equipment. The current remedy is simply to broadcast seed and hydromulch to bare slope. Too often, these techniques result in marginal plant establishment since germination and initial seedling survival is limited by nutrient poor, rocky substrates characteristic of cut slopes. The resulting poor vegetation establishment leads to increased erosion and sedimentation, occasional slope failure, increased noxious weed growth, and low aesthetic quality, substantially increasing maintenance costs in the affected areas. The Montana DOT (MDT) is investigating methods of organic matter application and incorporation to steep slope areas and establishing experimental plots to test compost application with blowers and incorporation on steep highway cut slopes at three sites, including heavy clay soils, glacial till, and coarse textured valley fill materials. [N]

 

4.12.9 Monitoring and Evaluating Vegetation Establishment during Construction
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Even after good practice is employed in the selection, delivery, and planting of stock, survival and normal growth depend, to a large degree, upon appropriate care during the establishment period. Consequently:

  • The establishment period should encompass the time required by the planting to become acclimated to the growing conditions at the planting site.
  • The Project Specifications should clearly indicate the length of the establishment period, which may vary from one area of the state to another, depending on the local conditions, climate, and the type of plant materials utilized.

A well-rounded program of horticultural practices used during the establishment period may include watering, adjusting emitter locations, fertilizing, pruning, insect, disease, and weed control, and replacement of unsatisfactory plants in accordance with the Specifications.
Arizona DOT recommends that the following items be observed and documented every 30 days during establishment:

  • Plants must be kept in proper position as appropriate for the species. Plants may require repositioning as a result of settlement, wind action, vandalism, etc. Care should be exercised in straightening to minimize disturbance to the root mass and should include replacing topsoil as required.
  • Stakes should be firmly embedded; redriving may be necessary. Stakes should not be allowed to rub the tree.
  • Guy wires must be adjusted to allow some movement. Adjustments may be necessary to keep the tree straight (not too tight) to prevent a large amount of swaying and prevent damage by rubbing.
  • Protective wrapping on trunks or stems should be secure.
  • Vehicular, fire, or damage due to vandalism should be noted and corrective action taken.
  • Note damage caused by animals (i.e., deer, rodents) and seek advice from Natural Resources Section on control measures. Damaged material should be replaced as necessary.
  • Report infestations of insects and disease to the horticulturist or other appropriate professional for recommendations on corrective action.
  • Inspect for broken branches or sucker growth and have them removed by pruning.
  • Where discoloration or foliage occurs, especially in evergreen material, advice on corrective measures should be sought.
  • Dead and severely damaged plants should be removed immediately and replaced within 21 calendar days.
  • Inspect for settlement of soil or soil mix and replace to required grade, repositioning the plant if necessary.
  • Inspect berms and water basins (constructed for the purpose of retaining water) to ensure that they are functioning properly. Repair and rebuild as necessary.
  • See that project areas are weeded, mowed, or sprayed as specified.
  • If planting projects require the use of fertilizers, specifications should be followed.
  • Qualified personnel, utilizing the best horticultural practices and tools, should perform pruning at the appropriate time.
  • A pre-final inspection should occur approximately one month prior to the end of the plant establishment period. The Contractor should correct any deficiencies within 10 days.
  • A Final inspection at the end of the Plant Establishment Period will be made to determine if all plants are growing in a healthy manner. There should be no problems at this time if the plants were well maintained during the course of the establishment period. The Resident Engineer or a representative, a Landscape Architect, a maintenance person, the Inspector and Contractor should attend this final walk through.

 

4.12.10 Performance Measures for Vegetation Establishment
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DOTs and Landscape Architects frequently establish site specific performance measures for vegetation establishment. A few DOTs have established organization-wide performance measures. Missouri DOT (MDOT) evaluates contractors' performance during construction via a questionnaire, one section of which is devoted to roadside development. [N] Whether seed and mulch application, soil preparation, lime and fertilizer application, and/or sod installation were in compliance with the contract and the percentage of sod living at the end of the initial watering period.

 

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Table of Contents
 
Chapter 4
Construction Practices for Environmental Stewardship
4.1 General Construction Site Stewardship Practices
4.2 Work Area
4.3 Construction Involving Historic Properties and/or Other Cultural Resources
4.4 Construction in and around Drainage Areas and Streams, Wetlands, and Other Environmentally Sensitive Areas
4.5 Erosion and Sedimentation Control
4.6 Vehicle Fluid, Fuel, and Washwater Control
4.7 Air Quality Control Practices
4.8 Noise Minimization
4.9 Materials Storage, Collection and Spill Prevention on Construction Sites
4.10 Vegetation Management in Construction
4.11 Soil Management in Construction
4.12 Establishing Vegetation at Construction Sites
   
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