PHOTO of an Edmonton British Columbia septic field in a low wet area, close to a small lake, and with trees in the field area - all bad ideas Planting Ground Coverings Over Septic System Components - an illustrated guide

This septic system design and maintenance article discusses the types of plants that should or should not be planted over or near septic fields or other septic system components. Planting trees, shrubs, and even some ground covers over septic system components are causes of septic system failure in the drain field, leach field, seepage bed, or similar components.

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Planting Ground Cover Over Septic Fields

There are several problems that can be caused by planting the wrong thing on top of or too close to septic system drainfields or soakaway beds. Among these we are concerned with possible sewage pathogens that may enter and contaminate edible fruits or vegetables grown on or too close to septic fields, and we are concerned as well that the roots of plants too close to the septic system can invade and clog system piping, leading to costly septic field repairs.

But here we address a less well known but equally important problem: some plantings can interfere with moisture evaporation from the soil below - transpiration: the movement of septic effluent moisture from the soil into the air by evaporation. Transpiration is an important ingredient in wastewater disposal in many septic system designs.

What Ground Cover Should Not Be Planted over Septic Systems?

Photograph of pachysandra ground cover  © Copyright DJ Friedman 2007 Photograph of Icelandic ground cover north of the artic circle

Ivy, Pachysandra, Similar Ground Covers are NOT OK for use over a septic drainfield: these plants will reduce effluent evaporation from the drainfield, soil absorption system, soakaway system, or mound soils. A second reason to keep these plants away from septic system fields is because their roots often invade and clog effluent distribution piping.

The photographs above show pachysandra as a dense ground cover (at left) and typical ground cover north of the arctic circle in Norway (at right). Thick dense vegetation of any sort will conserve moisture to itself and will prevent soil transpiration.

Photograph of Vermont wildflowersOver a septic system this means that the portion of effluent disposal that is supposed to be occurring due to evaporation will be reduced and the liquid load on surrounding soils increased - you've cut the effectiveness and shortened the life of the drainfield by such plantings.

These plants are OK, however, for planting over the septic tank itself.

What Ground Cover is Acceptable for Planting over Septic Systems?

Wildflowers and ordinary grasses are just fine for planting over a septic system and any of its components.

These are shallow-root plants that do not invade the system piping, they stabilize the soil surface, and they do not interfere with soil transpiration, the movement of needed oxygen into the upper soil layers (needed by the soil biomat below the drainfield) and the evaporation of a portion of septic effluent that enters the drainfield.

The photograph shows a field of wildflowers in northern Vermont.

Planting fruit trees, or vegetables (or anything else edible) over the septic drainfield might produce food that is unsafe to eat:


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