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Saturday - January 03, 2009

From: Conroe, TX
Region: Southwest
Topic: Erosion Control
Title: Plants for erosion control in East Texas
Answered by: Nan Hampton

QUESTION:

We have recently moved to Conroe and are having a problem with erosion behind a retaining wall (installed by previous owner. The retaining wall is made of concrete and is about 8 foot tall by 110 foot long.) that separates our back yard from a small creek. I have been reading about corrective actions, but am not sure what method is best. As far as I understand, at this point I need to fill eroded areas with crushed granite, cover with topsoil, spread grass seed, then cover with fiber roll. My question is; is this the correct thing to do and what grasses, or perennials (we like having herbs around) would grow best in this unstable, and very shady area? Oh, also, do you know where a person would purchase Fiber Roll?

ANSWER:

Your plan sounds like a good one although I am not sure whether the crushed granite is necessary. I would think it depends how deep the erosion is whether you need that addition. If you are filling in more than a few inches, it is probably necessary to add the crushed granite. Otherwise, I would think topsoil would be sufficient. The fiber roll or erosion blanket should serve to hold the soil in place until the grasses have become established. 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 also 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. Here is some information about fiber rolls and erosion control blankets. It is possible that large garden supply/landscape supply centers would have these products. Since you live near Houston, you might try calling some of those in Houston to determine availability there. You can search in our National Suppliers Directory for nurseries and landscape companies in or near Houston that specialize in native plants. The Houston Chapter of the Native Plant Society of Texas also has a list of Sources of Native Plants in the Houston Area. You can also search on the internet for manufacturers of erosion control blankets and contact them for distributors in your area. You are correct that grasses are ideal for stopping erosion because of their extensive fibrous root system. You can also add other plants along with them. Now for plants to use in your shady areas, you can find a list of "commercially available native plant species suitable for planned landscapes in East Texas" by selecting that area from the map or the pull-down menu on our Recommended Species page. You can use the NARROW YOUR SEARCH option to select plants that meet your requirements. For instance, you can select 'Grass/Grass-like' from the "Habit (general appearance)" and 'Shade' under "Light requirement". Here are some grasses from that list, as well as others that I have selected, that will grow in the shade.

Grasses and grass-like plants:

Bouteloua curtipendula (sideoats grama) grows 2-3 feet tall

Chasmanthium latifolium (Inland sea oats), 2-4 feet and has an attractive appearance even after it browns in the fall and winter

Sorghastrum nutans (Indiangrass), 3-8 feet

Carex blanda (eastern woodland sedge), not technically a grass, but it is grasslike and makes a good ground cover less than 2 feet tall

Elymus canadensis (Canada wildrye), 2-4 feet

Muhlenbergia schreberi (nimblewill), a low-growing (usually less than 1 foot) attractive grass that loves the shade

Herbaceous plants that will grow in the shade. You can sow their seeds along with the grass seeds:

Salvia coccinea (blood sage)

Rudbeckia hirta (blackeyed Susan)

Phlox divaricata (wild blue phlox)

Coreopsis lanceolata (lanceleaf tickseed)