Extension question: Can I garden on top of my septic system?

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While it’s still technically winter, the days are gradually getting longer and home gardeners are likely counting the days until spring. A recent question was posed to Dr. DeAnn Presley, Soil Management Extension Specialist, about gardening on top of a septic system. Since there are an increasing number of suburban homes being built in Kansas, most of which are not on municipal sewer systems, this article was written to help educate the public about residential septic systems and how to properly manage them.

How does a septic system work?

Septic systems, also referred to as onsite wastewater systems, treat and cycle wastewater back into the environment. There are many different kinds of systems, but except for lagoons, all depend on dispersing partially treated wastewater called effluent into the home’s lawn through a network of pipes called the drainfield or absorption field. Soil organisms, such as bacteria and fungi, play a critical role in decomposing the chemicals, compounds, and other organisms present in the wastewater. For this process to proceed efficiently the soil profile needs to be aerobic, meaning that the soil isn’t permanently saturated. That’s why systems have the large footprint that they do, so that water can be spread out across the dispersal field in such a way that there is not any one spot that’s overloaded with water.

Because of all this water, plants are very beneficial for removing some of this water from the lateral field through transpiration (water moves from the roots and exits through the leaves). However, the very best plants for covering a wastewater system components, such as the septic tank and the absorption field, are lawn grasses and other ornamental plants with a shallow root system.  There are a few reasons for this.

  1. It’s best to keep the area around the septic tank free of major landscaping or objects because the tank needs to be accessible for occasional pumping.
  2. Plants with large roots such as trees or shrubs might cause damage and/or plug either the septic tank or lateral lines with roots.
  3. From a human health perspective, vegetable gardening isn’t recommended. According to the EPA, “It is not recommended to plant trees, shrubs, or vegetable gardens on the drainfield. Tree and shrub roots can ensnarl and damage drainfield pipes. Vegetables can potentially be exposed to sewage effluent and be unsafe to consume. Native grasses and ground covers are the most appropriate planting over your drainfield.”

Because there’s always a risk that a septic system might be malfunctioning, it’s best to avoid consuming vegetables that could have been in contact with effluent.

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DeAnn Presley, Soil Management Specialist

Tags:  wastewater drainfields