Grass to cover a septic drain field

Asked July 23, 2019, 2:00 PM EDT

Could you please recommend a grass that is well adapted to the little rainfall east Medford receives during the summer months? We are installing a septic drain field on a west facing slope with full sun & clay/sand soil. I've read that covering the drain field with grass may prevent erosion, help with oxygen exchange, promote soil moisture removal through transpiration and keep out weeds. However the root system can't be too deep and the grass can't require irrigation. Starthistle is starting to spread so we need a competing plant but we can't irrigate over the drain field.

Jackson County Oregon

1 Response

You have one of those questions that is very difficult to answer: you sunny,hot, east Medford, is almost impossible to grow without irrigation, yet you can't irrigate, because it is on a septic leach-field. You want shallow-rooted grass so you don't disturb the leach-field. Unirrigated grass will extend its roots downward to find moisture (witness football fields built over 18" of sand, so the turf is resilient because of the long roots.) Please refer to the following studies that discuss your issues: This pdf is a Washington State University study full of information. Keep in mind, however, that much of Washington receives more rain in summer than we do. There are also several publications from Oregon State Extension that you will find helpful: EC1550, "Practical Lawn Establishment and Renovation" and PNW299, "Turfgrass Seeding Recommendations". You might also consider ground-covers such as Creeping Thyme, Creeping Oregano (Marjoram), or a mix of non-thirsty grass such as Buffalo grass, along with decorative rock, and succulents. The Jackson County Water Conservation folks may also have information regarding planting over or near leach-fields. They can be reached at 541-776-4267. Having lived in the western part of the county on an oak-dotted hillside for 25 years, with a leach field on a slope below the house, I can offer you our experience: let grow what grows naturally over the leach field.Get rid of that starthistle by mowing (don't let it bloom). You can't do much to kill it off other than using weedkillers or hand-pulling once it has bloomed. Every year, when whatever grasses (and weeds and wildflowers) have come up naturally, mow it short when it browns to protect against wild-fire. Yes, we didn't have a "green" landscape all summer, but a very natural looking one and we never had problems with our leach-field. Good luck with finding a solution that works for you.