Why You Should Revegetate Your Leach Field

By Suzy Crowe, Master Gardener

Whether you have an existing leach field or are constructing a new one, leaving the leach field bare of vegetation can immediately can lead to big problems. Planting a leach field helps the system to function properly, improves the look of a large open area, and controls noxious weeds.

Understanding how a leach field operates helps you determine what, how and when to plant. A leach field is a series of perforated pipes lying in a bed of gravel buried 15 to 18 inches deep. All household drains lead to a purifying tank. The waste is gravity fed through these drainage pipes and seeps into the leach field where the effluent is purified by the soil. If the soil in the field is clay or compacted, your pipes are clogged or your system is just not working properly, the effluent may not drain as efficiently. Revegetating the field with native grasses and wildflowers can help the system to function properly by pulling moisture out of the soil through evapotranspiration. When it comes to planting on a leach field, the effluent should not be a problem if the system is working properly. Any bacterial or viral contamination should be percolated down into the soil. If the effluent isn’t percolating properly it may rise to the surface contaminating the soil. However, it is hard to determine if your system is functioning properly.

Leach field soil may also be highly alkaline not only because of the effluent but also because many household cleaning products are highly alkaline. Since all drains lead to the leach field the soil tends to have a high PH level. Have soil tests done before planting to determine if their will be problems with your soil. The PH level may also indicate if your system is working properly.

So what plants are the right plants for a leach field? Low maintenance, low water, shallow rooted plants that grow in a variety of soil types (salt-tolerant) are most suited to this site. Trees and shrubs may clog the drainage pipes and cause your system to malfunction. Vegetables, although tempting to plant since leach fields get a large amount of sun, are a poor choice due to the percolation issues discussed above. A raised bed of veggies is also not a good choice. A raised bed eliminates the problem of questionable soil, but inhibits the evapotranspiration of moisture from the field that helps the septic system function properly. Standard perennials might not be a bad choice, but may be more high maintenance than you want. As well, leach fields are generally located in a place on your property that is tucked away and your perennials not enjoyed.

The best choice is a native grass and wildflower mix. They are best suited to the disturbed soil and lack of water. They take less maintenance and their rapid spread can cover a large leach field in no time. Seeds should be sown in the fall. Make sure you remove all existing weeds before sowing so you start with a clean slate. The soil should be loosened a few inches down. Sow the seeds by hand. Mixing the seeds with a little sand helps distribute them evenly. Cover the seeds with the soil you tilled. Avoid bringing soil in from another location on your property because it may come with some new weed seeds and new problems. Covering the planting with a little mulch helps water retention and keeps the wildlife out. The following spring when your seeds germinate, monitor your new wildflower meadow for weeds as their seeds may take a season to germinate.

Controlling a weed problem before it happens is easier than eradicating a weed problem after you have one. The choice is yours. Put the time and effort into it from the get go and avoid problems down the road. I learned the hard way. I installed a new septic system and vegetated it the following fall only to find that when the seeds germinated the following spring, so too did all the weed seeds that had lain dormant a full season. One sore back later, the existing weeds were gone before they went to seed. But had I vegetated my leach field the first season, I would’ve saved my back. The moral: save a back, kill a weed.