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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 - (C) Daniel FriedmanPlanting Ground Coverings Over Septic System Components
an illustrated guide

Ground covers that can be planted over septic fields:

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

Photograph of pachysandra ground cover  © Copyright DJ Friedman 2007There 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

  1. Possible sewage pathogens that may enter and contaminate edible fruits or vegetables grown on or too close to septic fields

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

    see SEWAGE CONTAMINANTS in FRUIT / VEGETABLES for details.

  2. Invasive 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 an additional, less well known but equally important problem:

  1. Blocked soil transpiration - 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 Kinds of Ground Cover Should Not Be Planted over Septic Systems?

Avoid planting invasive rooted, deep-rooted or large heavy plants over the drainfield or where they would interfere with septic tank maintenance.

Avoid planting projects that would require driving or even heavy foot or animal traffic over septic mounds and raised-bed septics.

Details of what to avoid over the septic soakaway

Photograph of Icelandic ground cover north of the artic circle

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.

At TREES or SHRUBS OVER THE SEPTIC FIELD or TANK you will find tables of various plants that can or that should not be planted over septic soakbeds or drainfields and we include detailed data about plant root depth and root spread distances. From that information you'll see that some plants should not even be located near the septic drainfield.

What Ground Cover is Acceptable for Planting over Septic Systems?

Plants that are light in weight, not so dense as to block soil moisture evaporation, and that do not grow large, such as into trees, and that use a shallow root system that is not likely to reach the depth of the top of the drainfield trenches and that are not producing edible food are fine over a septic drainfield.

Photograph of Vermont wildflowers

The photograph just shows a field of wildflowers in northern Vermont.

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

Wildflowers and most grasses 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.

Watch out: some ornamental grasses have a very deep root system and should not be planted over your septic fields or soakaway.

Fern garden planted over the septic drainfield (C) Daniel Friedman Amenia NY

Above: ferns growing over a septic drainfield in Amenia, New York.

Owners of this property report that the prior owner told them that these ferns are atop the property's septic drainfield. In the ensuing decade there were no reports of septic failure nor signs such as a sewage odor in this are, but we note that

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Question: flowers at the septic field borders burn up

(Mar 5, 2014) BJ said:
Why do the flowers planted at the very end of a septic leach field eventually appear to have 'burned up' and what can be done to prevent this? Are there any particular flowers that will work better (perennials for sun)?

Reply:

BJ

Thanks for the question, but sorry, I don't know but I suspect that your drainfield is sending a higher concentration of nitrates and nitrites to its borders - which is common as the leach lines slope down towards their ends. Check the soil nitrate levels to see if they're out of bounds.

Thinking in an opposite direction, also check moisture levels; it would be odd but possible that at your property that area is just too dry for the plantings, OR the opposite could be the case - excessive septic effluent may contain detergents or something harmful to the flowers.

I can't recommend specific plants partly because it's not my expertise and partly because it would be risky to recommend something without inspecting and testing the soil in the area you describe.

Question: playing horseshoes over the septic leaching bed or soakbed

(June 23, 2014) Anonymous said:
I want to put in a horseshoe court and it may be over part of my septic leach bed.
My question: I have to drive two steel stakes about a foot down in two places. Will this damage my bed or make it not work?

Reply:

(June 23, 2014) (mod) said:
Anon you're probably OK, as I'd expect the septic soakaway bed or leachfield pipes to be more than 12" down in the soil. Certainly if you punch a hole in a pipe that's not good - breaking the pipe and inviting a leak.
If you can see the actual location of the trenches by noting the depression lines that often mark their path, be sure to locate your horseshoe court stakes between rather than over the trenches.


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