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Thursday - September 06, 2007

From: Maple Valley, WA
Region: Northwest
Topic: Erosion Control
Title: Erosion control plantings in Washington state
Answered by: Nan Hampton

QUESTION:

Hi, I am trying to do an eagle project that involves putting vegetation onto a hill to prevent erosion. I live in Washington state where there is plenty of rain so erosion is a big problem. We are trying to work with dirt that rarely gets watered except by rain, and is extremely rocky. What kinds of plants would hold together a hillside and could be planted in abundance for cheap?

ANSWER:

The best plants for controlling erosion are grasses because of their extensive fibrous root systems. Below are grasses native to King County Washington that should work well for your project.

Agrostis exarata (spike bentgrass)

Bromus carinatus (California brome)

Danthonia californica (California oatgrass)

Deschampsia caespitosa (tufted hairgrass)

Dichanthelium acuminatum var. fasciculatum (western panicgrass)

Elymus glaucus (blue wildrye) — especially recommended for erosion control

Festuca occidentalis (western fescue)

Koeleria macrantha (prairie Junegrass)

The cheapest way to carry out your project is by sowing grass seeds. However, since you would be sowing the seeds on a hillside, rain is likely to wash the seeds away before they have had a chance to germinate. You might be able to find grass plugs available for sale. They will be more expensive than the seeds but would have a better chance of setting their roots before rain could wash them away. Another (alas, more expensive) possibility is to use erosion control blankets to stabilize the erosion area. The erosion-control fabric works by slowing the runoff water and allowing sediments to fall out rather than be washed away. Seeds are sown under the erosion-control material and grow up through the matting when they germinate. You can insert plants into the soil by cutting through the matting. The roots of the plants that are growing through the erosion-control material anchor the soil to stop the erosion. If you use erosion-control blankets made of biodegrable material, they will eventually disappear leaving the plants to control the problem. You can read about a stream bank stabilization project implemented by the Department of Environmental Services, Arlington, Viriginia.

You can check our National Suppliers Directory for possible sources in your area for grasses and grass seeds.