Native plants suitable to grow near a drainfield?

Beth Clawson<Clawsonb@msu.edu>, Michigan State University Extension - June 02, 2024

Landscaping over your Septic system whether a formal garden or informal one can be tricky. You want to have a beautiful yard but not at the expense of damaging your onsite waste water system.

Yarrow and Echinacea are popular flowering native plants. Photo by Beth Clawson, MSU Extension.

Most Michigan rural homeowners have an onsite waste water system (septic system) that includes a septic tank and water drainage field to dispose of the treated water. In a state with over 1.3 million septic systems, placement of the septic system for homeowners can be located in either front, side, or back of the home and take up much of the yard space. Landscaping over the tank and drain field should be approached with care and to remain mindful that it is installed just below the ground surface. Following a few do’s and don’ts will protect your onsite water treatment system and still provide you with the landscaping you want.

Part of the confusion with using native plants over a drain field is that recommendations vary. One source will emphasize using only shallow rooted flowers and grasses over the drain field. Others suggest just lawn grass thus requiring water inputs to maintain a healthy lawn. Still others recommend using plants that are drought resistant so the mound does not have to be watered. However, a lot of native plants (at least the drought tolerant grasses) have root systems that go very, very deep. To the average homeowner this mix of information can be confusing.

“One grass recommendation for planting on the drain field was Big Bluestem. I think that the root system can go as deep as 15-20 feet and has fibrous roots. That seems to contradict the "shallow root system" recommendation!” exclaimed a client.

About septic systems

Native plants, like any plant in your landscape, should be chosen and placed with consideration of its proximity to the septic system. Before you start your landscaping project, make sure to have an understanding of the basic components of the septic system. The two most common septic systems in Michigan are subsurface trench systems and mound systems. Both systems have plumbing exiting the house to a septic tank for initial separation and partial treatment. From there, the wastewater minus its solids either drains by gravity or is pumped into a

Soil absorption or drain field consisting of several trenches lined with perforated pipe on a gravel bed or a
A three to four foot mound of sand above ground level encasing a drain field.

Properly designed, these fields are engineered to drain the external water from rain and snow melt away from the field rather than into it. This creates a situation where the surface soils in the drain field are drier than in other areas in the landscape. This means that the plants you place there should be drought tolerant.

Avoid heavy walking or driving traffic over your drain field. This compacts the soil, inhibiting its ability to adequately drain the water. It also reduces the pore space necessary for aerobic microbes that help to treat the wastewater. Never install an irrigation system over your drain field. Adding additional water to the area risks over saturation. Note: If your drain field area is wet, has standing water, or water collects there after a rain, it is strongly recommended that you stop here and call for a septic inspection. You may be experiencing a septic system or drain field failure.

Choosing plants that do not interfere with septic system operations

Choosing the right plants for a particular site is key to successful landscapes. When choosing native plants for over drain fields, choose those suited for a dry prairie. You can get plant material either as a seed mix or selected plants and plugs. Native plants will absorb the additional nutrients in the soil preventing them from readily entering the groundwater. Additionally, the roots of dry prairie plants do not clog septic system pipes because they do not thrive in water saturated conditions. Avoid using any plants that require moist or wet soils. These plants seek additional moisture and will likely invade open pores and pipes.

Turf grasses are the most common plant selected for over a septic system. However, their shallow roots require frequent surface watering, and require repeated lawnmower traffic to keep the lawn trimmed. Choosing a native garden is low maintenance, requires no fertilizer, mowing, or watering. It does require some weeding and removal of seasonal dead vegetation. As an added bonus it will attract butterflies, bees, and other wildlife to your yard.

A few choices for a short grass dry prairie, may include:

Wildflowers & Forbs: For sunny spots: Butterfly Weed, Sky Blue Aster, Smooth Aster, White Aster, Sweet Everlasting, Canada Milk Vetch, Lance leaf Coreopsis, Purple Prairie Clover, Pale Purple Coneflower, Rough Blazing Star, Royal Catchfly, Lupine, Dotted Mint, Beardtongue, Black Eyed Susan, Wild Petunia, Stiff Goldenrod, Showy Goldenrod, Ohio Spiderwort, Hoary Vervain, New Jersey Tea, Lobelia, Flowering Spurge. For shady places consider: Astilbe, Hardy Begonia, Turtle Head, Ferns, Sweet Woodruff, and Lady’s Mantle.
Grasses, Sedges & Rushes: Sideoats Grama, Little Bluestem, Prairie Dropseed, Plains Oval Sedge, June grass, Prairie Brome.
Shrubs & Trees: These are not recommended over any part of a septic system. If you do choose to plant trees and shrubs, always choose an upland variety and plant it far enough away so that the dripline of the mature tree will fall outside the drain field or mound.
Bulbs: Arum, Anemone/Windflowers, Crocus, Hyacinth, Iris, Lilies, Daffodils, Tulips. (Note: some bulbs listed are naturalized but not all are native.)

Finally a few reminders:

Avoid growing water loving plants, shrubs, and trees near your septic system.
Do not grow vegetables over your septic system because of the risk of bacterial contamination and the health risks associated with it.
Do not add additional soil to your drain field. If the soil in your drain field area is consistently damp, has standing water or you experience water backing up into your home, contact your County Health Department or septic service provider for an inspection. Your field may have failed.
Keeping a layer of vegetation over your drain field is recommended to hold the soil in place and maintain a functioning system.
Avoid heavy tilling of the soil when planting. You may disturb or damage your drain pipes.

More resources for planting over septic systems:

Michigan State University Extension: For a general list of Michigan Native plants.

Purdue Extension Bulletin HENV-15-W: For an overview and plant list. http://indiana.clearchoicescleanwater.org/uploads/88/docs/5989septic_landscaping.pdf

Clemson Extension Bulletin: For a plant list and some tips.

Michigan Department of Environmental Quality: Michigan specific information about septic systems.

If you observe signs of trouble from your septic system, call your County Health Department immediately and have your septic system pumped and inspected as soon as possible. For more information about how to manage your septic system visit the MSU Extension Septic System Education website.