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Temporary Seeding

General

Temporary seeding stabilizes disturbed areas with fast growing annual grasses, small grains, or legumes until permanent vegetation can be established. Dense, established vegetation protects the soil from raindrop impact, reduces flow velocities, increases infiltration, reduces soil loss from the site and is the most effective erosion control practice available. In addition, temporary seeding is economical and adds organic matter to the soil and reduces dust and mud problems that are common on many construction sites.

Temporary seeding is applicable on any area of the site that will remain inactive for at least 14 days, but less than 1 year. It is often used to prevent erosion between construction activities and during the winter months if established early enough. Due to its short-term nature, temporary seeding may be ineffective on its own and should be used in conjunction with other management practices.

Advantages

  • Cost-effective
  • Easy to Apply
  • Requires little maintenance
  • Increases infiltration and water retention
  • Adds organic matter for permanent seeding
  • Reduces dust

Disadvantages

  • Use limited by the growing season
  • Maximum life span of 1 year
  • Requires the addition of fertilizer on infertile soils

Design

Vegetation

Temporary vegetation provides effective erosion control only once densely established. “Dense” is defined as a stand of 6-8 inch vegetation that uniformly covers at least 70% of a representative 1 square meter plot. Until vegetation is permanently established on site (generally 60 days after it has been planted) it should not be relied upon to prevent soil loss.

The species of vegetation selected will vary depending upon the soil type, slope, and the time of year it is applied. Common types of temporary vegetation include Wheat, Rye, Spring Oats, Annual Ryegrass and Sudangrass. These annual species establish themselves quickly under the proper growing conditions and require minimal maintenance. Care should be taken when selecting a species to avoid the use of exotic or invasive species, as they may upset the balance of the local ecosystem.

The seeding rates, depths, and times of application supplied here are intended only as general guidelines. All manufacturers’ guidelines should be carefully followed to ensure the success of this practice.

Seedbed Preparation

To be successful, permanent seeding requires a properly prepared seedbed. Areas that are limited by poorly drained soils, steep slopes, or that allow concentrated flow to develop should not be used for seedbeds unless amendments are made.

Soils should be tested for nutrient content and pH to determine the amount, if any, of fertilizer or lime required. Over-application of these soil amendments is costly, ineffective, and may cause serious pollution problems. As a result, lime and slow releasing fertilizers should be applied only as needed and should be incorporated into the soil to keep them on site and in the root zone.

The organic content of the soil is also an important consideration when preparing the seedbed. Soils rich in organic matter possess high levels of nutrients and microorganisms, which improve the growth rate, require less fertilizer to be applied, and increase the porosity of the soil. To improve the organic content of the soil, organic compost may be incorporated into the top ten inches of soil.

A minimum of 3-4 inches of topsoil is required for permanent vegetation. It should be loose, uniform, and well pulverized to promote rapid growth. Compacted soils should be loosened to a depth of at least 6-8 inches by using a chisel plow or similar implement to ensure adequate pore space.

Application

Seed should be applied uniformly following the supplier’s recommendations by broadcast seeding, hydroseeding, or drill seeding. Broadcast seeding involves scattering the seeds on the soil surface by hand or mechanical means and is best utilized on smaller areas and for patching applications. After application, the site should be raked and firmed with a roller or cultipacker. Seeded areas should then be mulched to provide protection for the seed and to reduce erosion before the vegetation becomes established (refer to Mulching).

Hydroseeding and drill seeding are more costly than broadcast seeding and are used on larger sites to maximize the application’s cost effectiveness. Hydroseeding, a method that mixes the seed and water together into a slurry, is applied on areas that may be difficult to seed with alternative means. Other amendments, such as tackifiers, polymers, fertilizers, and/or fiber mulch are often added to the slurry, which is sprayed on, to protect the seed and to promote its growth. Drill seeding utilizes a drill or cultipacker seeder to inject the seeds beneath the soil surface. Seed depth is set based upon the supplier’s specifications, but generally is ¼ - ½ inch deep for grasses and legumes. Drilling, while more costly than broadcast or hydroseeding, is generally very effective when performed properly because the seed is protected from wind, water, and wildlife.

Construction

  • All tracking and grading should be completed before temporary seeding begins
  • All management practices should be installed and online before seeding
  • Seedbed should be adequately prepared before seeding begins
  • To promote growth, seeding should not be performed during excessively wet conditions, as soils may become excessively compacted

Maintenance

  • Inspect seeded areas weekly after planting to ensure that vegetation is adequately established, reseed as necessary
  • Seeded areas should be inspected after each rainfall event to check for evidence of erosion and bare spots
  • Add fertilizer as necessary at proper rates
  • Water seeded areas regularly until they become established

Method to Determine Practice Efficiency

The efficiency of this practice is derived from reducing the amount of time that the site is left bare and exposed. To determine the efficiency for this practice, use the new, shortened exposure time and replace the pre-existing one in the USLE and recalculate. The difference between the two equations is the efficiency for the practice.

References