Planting over a septic system
Radio interview source: Dr. Susan Day, urban foresty expert, Virginia Tech
Planting the area over your septic drain field probably isn't at the top of your landscaping to-do list, but maybe it should be. If grass bores you, try shallow-rooted herbaceous plants like flowers and ground cover. The right plants (like echinacea, pictured here) can help prevent erosion and expel liquid and nutrients from the soil, allowing the septic system to function more efficiently. Of course, you don’t want a jungle on top of it because the septic guy has to get in there and suck it out every few years.
Virginia Tech Urban Forestry expert Susan Day says before you get the spade out, there’s something you have to check out first.
"You don’t want to be digging down into the drainfield so you need to know how deep it is and you need to know where it is. So if you’re going to be digging in the soil there, you don’t want to go down where you’re going to interfere with that gravel envelope that’s around the pipes. Knowing how your drainfield is constructed is very helpful and most people don’t know that."
Some septic lines are just six-inches under the surface, so roto-tilling and double-digging are out. You also don’t want to plant something that needs to be divided frequently. The less you have to dig, the better. The nice thing is that by planting over your septic system, you won’t spend much time watering or fertilizing, if at all.
It also might seem to be the ideal place for a nutrient-loving vegetable garden, but there is the concern about bacteria contamination. A lot depends on how well your soil filters the bacteria. Clay soils work best, eliminating bacteria within a few inches of the drain trenches. Sandy soils allow the organisms to move several feet. A septic system that’s working right won’t contaminate the soil with nasty organisms, but it’s very difficult to tell if it’s operating as it should be. So, it’s best to avoid planting certain vegetables.
"I would not grow root vegetables," warns Day. "You could and it would probably be fine, but as just a precaution I wouldn’t do that. You could grow other kinds of vegetables and I would just make sure they are mulched so you don’t have bare soil there. You don’t want to have the soil splashing on your vegetables."
Above-ground plants like tomatoes, beans and peppers are safer since the soil won’t splash up and contaminate them.
Learn more about planting over your septic system:
Planting on your septic drain field: Learn which shallow-rooted plants are best for removing moisture from the soil and preventing erosion over a septic field.
Landscaping septic systems: This guide explains where to plant on and around mound septic systems, and offers a list of preferred native plants and grasses.
Landscaping your drain field: Browse this list of plants suitable for planting on a mound or standard drain field, broken down by the amount of sunlight the area receives.
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