Seeding

Description and Functions

Seeding involves the application of grass, forb, and woody plant seed mixes to slope areas. Seeds may be applied to slopes by broadcasting seed mixes onto the slope by hand or by placing seed into small holes placed into the slope. Hydroseeding is also another option used for hard to access locations. Seeding creates a shallow fibrous rooting zone in the upper foot or so of the surface profile which binds near-surface soils and protect soil surfaces from surface water runoff, wind, and freeze-thaw erosive forces. Seeding is usually applied in combination with other planting techniques to address most erosion control issues.

Figure 8. Seeding (grasses shown here) with erosion control mulch.

Planning Considerations

Drilling soil holes into the slope area can reduce the seed quantities required. Practically, this method is best used on mild slopes, in smaller prescription areas, and for woody plant seed stock which is more expensive that grass seed mixes. Typically, a 3-inch diameter by a 4-inch deep hole is a good size for the planting hole. Make sure surrounding soil is loosened around the hole so that future root systems can develop. Drop a slow release fertilizer capsule to the bottom of the hole and cover with about 31/2 inches of soil. Then place about 20 seeds into the hole and cover the seed as directed by the seed supplier.

Broadcast seeding is the most common application method employed in projects. Seeds are scattered uniformly by hand onto the slope. If the application area soil has been roughened slightly, seed germination will be more successful. It is also important to make sure precipitation does not wash seeds down the slope. Mulch seed immediately to keep seeds from being blown and washed away, or eaten by wildlife, and to keep the surface soils moist. Fertilize areas as required by mix directions. Hydroseeding is another application method that uses seed mixed with water, fertilizer, and sometimes mulches to spray apply the mixture onto expansive or hard to reach slope areas.

Limitations

Good for mild erosion problems or in combination with other techniques. The shallow fine rooting systems of grasses and forbs do not significantly increase the shear strength of the surface soil profile and limit landsliding. Woody plants seeded into slopes need five to ten years to begin to develop extensive rooting networks. Woody plant roots do a better job providing root reinforcement of the surface soils but are less effective than native grass mixes at reducing erosion at the soil surface. Seed germination for all species require that soils to be kept moist. Seeding should include mulching to achieve adequate erosion control. Seed mixes using combinations of wild strawberry, wild ginger, oxalis, sword fern and bracken fern have been reported to be more successful than grass-based mixes for some sites.

Advantages and Disadvantages

  • Advantages: Seeding can be quickly applied to slopes, materials are inexpensive, and technique is compatible with many slope situations.
  • Disadvantage: Seeding does not readily self-repair eroding slope areas. Seeding is not adequate to be used alone for highly eroded areas or for shallow seated landslide stabilization.

Applicability

Compatibility

Key to Applicability and Compatibility Graphics (Figure 2)

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