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Saturday - April 16, 2011

From: Austin, TX
Region: Southwest
Topic: Grasses or Grass-like
Title: Plants to slow water runoff in Austin
Answered by: Barbara Medford


What native plants (rocky northwest Austin) will block water runoff? It seems as if something deep-rooted and densely growing would help. Grass comes to mind, but the area gets at best 2 or 3 hours of sun. Anything planted there would have to be able to contend with rock and drought most of the year. Am I looking for something that doesn't exist, or is there hope? Thanks!


Plants don't "block" water, you'd have to have a concrete dam to actually block the flow, and the water would still find a way to go around or over the dam. You can, however, slow the water down and allow more of it to soak into the soil, and have the impurities it has picked up along the way filtered out by the earth before the water goes into our water supply. You are correct in thinking that grass is the right thing to use, and you will be happy to know that there are attractive and useful native grasses that can do just fine in that much shade.

We are going to talk grasses, but there are other alternatives. Please read this very complete Rain Gardens - a how-to manual for homeowners.

We are going to direct you to our Recommended Species section, and teach you how to make choices there for yourself, although we will give you some examples. The Lady Bird Johnson Wildflower Center is dedicated to the growth, propagation and protection of plants native not only to North America but to the areas in which those plants grow natively. This is because a plant native to an area is already accustomed, by millennia of experience, to the climate, rainfall and soils of that area. This is a great conservation move, because artificial fertilizers, supplementary watering and chemicals will be needed in moderation, if at all.

Following the link above, you will get a page with "Narrow Your Search" on it, click on Central Texas on the map, and then check on types of plants, shade and sun conditions, even soil moisture. When you have checked all that are appropriate on the sidebar on the right-hand side of the page, click on "Narrow Your Search" at the bottom of the page, and you will get a list of plants that fit your requirements. If you put in too many conditions, you may get no selections at all, so you will have to compromise and figure out what you can do without or change in your specifications. You can organize the same Search for vines, trees, shrubs, ferns, succulents or ferns.

We will go to the Recommended Species, select Central Texas  part shade in Light Requirements and whatever else you think applies. You will get a list of 9 grasses recommended for Central Texas. Follow each plant link on that list to determine what soils that plant prefers, expected size of the plant, whether it is evergreen, bloom time and color, etc. If you don't like these, you should be able to do the same thing and find others you like better. We selected some that we already have some experience with, and checked the USDA Plant Profiles on each to assure that that each could be grown in Travis County, USDA Hardiness Zone 8a. If you need more local advice, contact theTexas Agri LIFE Cooperative Extension Service for Travis County. Here is a list of the grasses that we thought would do well for you:

Andropogon gerardii (Big bluestem) - 4-8 ft, tall, perennial, medium water use, sun (6 hours of sun or more) or part shade (2 to 6 hours of sun).

Chasmanthium latifolium (Inland sea oats) - 2 to 4 ft, perennial, medium water use, part shade or shade (less than 2 hours of sun daily).

 Nolina texana (Texas sacahuista) - 2-3 ft. tall, perennial, blooms white, green March to July, part shade.

Schizachyrium scoparium (Little bluestem) - 18 to 24", perennial, sun or part shade.

From our Native Plant Image Gallery:



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