Landscaping Over a Drain Field

Certain Plants can help your septic drainage system function properly.   Plant cover is also important to reduce soil erosion. At the very least the drain field should have a nice field of grass planted over it to help remove moisture and nutrients from the soil but with a little planning and work you can have a nice ornamental garden over your drain field that will not only be pretty to look at but will help to keep your septic drainage system functioning properly.

Vegetables Over a Drain Field?

There are some folks that believe you can plant vegetables if proper care is taken but I wouldn’t risk it as there is a chance of bacterial and viral contamination from the effluent. Different soils vary a greatly in their ability to filter viruses and bacteria from your field into the soil. Clay soils work the best, getting rid of  bacteria within a few inches of the drain field trenches, however, sandy soils may spread bacteria for several feet.  A properly operating system will not contaminate the soil with disease-causing organisms, but it is nearly impossible to determine if a field is operating at it's best.  If at all possible, use your septic drain field for ornamentals and plant your vegetables somewhere else.  If you must plant vegetables be sure to read everything you can find on the subject so your vegetables are safe to eat.

What about trees?

Long invasive roots can be very damaging to your drain field pipes.  If you want to be absolutely certain that tree roots will not intrude into your drain field, trees should be planted at least as far away as their root spread will be once they are fully grown.

No Raised Beds or Permanent Structures

Do not build raised beds over the field as they will inhibit evaporation of moisture. Also, you should not put in any permanent structure over your drain field as they will also inhibit evapoation and  these would all have to be removed in the event of a drain field problem where it would need to be dug up.  You also do not want to put livestock over your drain field.

What Exactly is a Drain Field?

 A drain field is a series of shallow, perforated pipes set in gravel trenches that allow septic tank effluent to drain over a large area.  As this effluent seeps into the ground, it is purified by the soil. Plant roots can help remove excess moisture and nutrients and make the purification of the remaining effluent more efficient. However, roots that clog the pipes will seriously damage the drainage field. 

Know Your Soil

It is important to know what your soil conditions before deciding on any landscape planting. You can get inexpensive pH testing kits at your local garden shop. 

The composition of septic tank effluent varies based on what goes down the drain. Many household chemicals are highly alkaline and can raise the pH of the effluent, although the salt levels are likely to be high no matter what the pH is, so plan to use plants that are somewhat salt tolerant.

Suggested Plants

Shallow-rooted plants such as flowering perennials and annuals, grass, and many ground covers are not likely to damage your pipes.

Some plants that are both salt and moisture tolerant include hollyhocks, bee balm, violets, arborvitae, red osier dogwood, and inkberry holly.  If your field is well drained, there are a number of salt tolerant species that should be suitable, including yarrow, columbine, chrysanthemum, delphinium, daylily, peony, clematis, and rose.

There are nice groupings of these seeds in something called a “meadow in a can” that can be found at your garden shop or hardware store.

There is really no need for the use of fertilizer on your drain field plants as the salts present provide plant nutrients like nitrogen, phosphorus, and potassium.

Cautions

Always wear gardening gloves when planting, weeding or doing other gardening activities that involve contact with the soil over your drain field. This will protect you from accidental contact with any harmful organisms that may be present in your soil.