Planting on Top of Septic Systems
Published: August 31, 2011
Q: We have a septic field at our cabin. I have heard we need to keep it cleared of excessive vegetation. Why is this important and how clear must it be? – Maureen, via e-mail
A: It might be helpful, first, to have a visual of a drain field (or leach field) in mind. Essentially, it is made up of a number of perforated pipes set in gravel trenches. The pipes are set to a shallow depth – some as little as 6 inches below the ground surface. As liquid effluent enters the drain field, it slowly seeps out, and it is filtered and purified as it percolates through the surrounding soil.
Vegetation on the drain field is extremely helpful for the simple fact that plants help prevent erosion. Plants also make the effluent purification process more efficient, by removing excess nutrients and dampness from the soil.
Even though plants are essential to the whole process, the wrong types or excessive growth can cause major problems, even septic failure. Why? Because plants that have woody roots (trees and most shrubs) can clog the drain field pipes, prevent the system from working as it should and, in some cases, shut the system down.
Ideally, what you want to see over a leach field are shallow-rooting herbaceous plants that aren’t, as the Virginia Cooperative Extension service puts it, “excessively water loving.” Native grasses and wildflowers (even weeds) are good examples of these types of plants: they keep the soil in place, but they don’t prevent the very important movement of oxygen in the soil and the evaporation of part of the effluent. And these plants won’t disrupt the pipes underneath. Their roots aren’t woody, deep or aggressive.
While there are some less aggressive shrub and tree species out there, stick with plants that you know aren’t going to do harm. For information on plants native to your area, contact your local cooperative extension office; they’ll likely have a whole list from which you can choose.