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Sunday - March 29, 2009

From: Lawrence, KS
Region: Midwest
Topic: Septic Systems
Title: Length of root systems for wildflowers over septic system
Answered by: Barbara Medford

QUESTION:

Mr. Smarty Pants: I want to know the length of root systems for native Kansas wildflowers that will be planted on a Wisconsin mound septic system, which is a special septic system partially above ground. The topsoil is 12-15" in depth so I need to know the root system length. Some flowers I have in mind are prairie coneflowers, black-eyed susan or variety of sunflower, purple prairie clover, Indian grass. Any grasses you can think of beside fescue, which is boring. This area will never be mowed or only very occasionally. Or if you can direct me to a website or reference book would be helpful.

ANSWER:

Sorry, but there is no definitive answer to your question. So far as we are able to determine, there is no list or database on root lengths of any plants, including natives. The root length of any plant is variable, depending on the plant size, genetics and age as well as environmental conditions. Keep in mind that when your system was designed, it was a well-known fact that something would grow over it-if not planted by you, then weedy volunteeers. If those volunteers are not eliminated, some of them are bound to be woody plants, and that's what you're trying to avoid.

All the research we consulted agrees that the best plant material for the earth covering septic systems is grass. They have fibrous roots and will help hold the soil in place, help prevent erosion on your raised system, conduct some of the moisture to the surface of the soil, and are easily maintained. Wildflowers will fall into the same category, particularly the annuals. The one thing you want to avoid is woody plants, especially trees, as they develop long roots that stretch out beyond the canopy of the tree and would go for the moisture in the septic lines. Those roots can certainly clog the lines, so keep the trees away.

We are going to go to Recommended Species for Kansas, select first on herbs (herbaceous flowering plants) in Habit and annual in Duration. We will then do the same thing in grasses, but not indicate a duration. Even perennial grasses are going to maintain a root system that is compatible with the septic system. If your area has a lot of shade, or you are interested in other species, you can do the same thing, putting in the different characteristics (like bloom time and color, for instance) and make your own selections. We included those on your list, all of which are native to Kansas and excellent choices.

Grasses for Kansas

Sorghastrum nutans (Indiangrass)

Andropogon ternarius (splitbeard bluestem)

Aristida purpurea (purple threeawn)

Bouteloua curtipendula (sideoats grama)

Bothriochloa laguroides ssp. torreyana (silver beardgrass)

Carex blanda (eastern woodland sedge)

Calamagrostis canadensis (bluejoint)

Chasmanthium latifolium (Inland sea oats)

Wildflowers for Kansas

Ratibida columnifera (upright prairie coneflower)

Rudbeckia hirta var. pulcherrima (blackeyed Susan)