septic mound landscaping

Asked August 18, 2020, 1:49 PM EDT

I would like to replace grass on my mound system with native plantings. What are my options for getting rid of the grass? And are seeds or plants the better option once grass is gone? Or just start to phase grass out by planting aggressive natives? Thank you for any advice.

St. Louis County Minnesota

2 Responses

Planting in the grass probably won't give you good results. You will have lots of grass growing through everything and making things look messy.

You can get rid of the grass with chemicals (a non-selective that kills everything), removal of the sod with a sod cutter, or by solarization. Solarization takes at least a summer, so might not be the best option for you.

Prairie Moon nursery specializes in natives and has a good article that explains how to clear a plot and plant natives. See https://www.prairiemoon.com/blog/site-prep. We don't recommend any vendors, so just see this as a recommendation of their methods.

I got a whole new septic system in June and decided to use a combination of plants and seeds. The plants helped stabilize the mound and kick started the project. The seeds saved money, but I am terrible at identifying the seedlings, so I probably have pulled as many natives as I left to grow. Many of the natives are best seeded in the fall, so I have a bunch waiting to go in in a few months. The same site explains the pros of spring and fall plantings.

I bought lots of native grasses in small plugs. Mary Meyer, who is an ornamental grass guru at the U of MN, said that fall plantings of small grass plugs don't do as well as spring plantings. In June I took some of the grasses bought in 6" pots and cut them into quarters. They will take longer to fill out, but it saved a lot of money.

It is important to plant drought tolerant plants on the mound. Not only is it a place you don't want to water once the plants are established, but the mound just has a thin layer of dirt over sand. Native grasses do well. Michigan has a good sheet on mound plant selector: https://www.canr.msu.edu/news/could-you-please-tell-me-what-native-plants-i-can-plant-on-the-drain-field. If you want to add some non-natives, https://hgic.clemson.edu/factsheet/landscaping-over-septic-drain-fields/ has a list of suggested varieties.

It is a big project, takes several years to mature, and can get quite expensive. But, for me, I am really happy with the look and glad I didn't go with the contractor's poor quality grass seed. If you decide to take the plunge I think you will be happy you did. Feel free to write again if you have any questions and good luck with your project.




Terri, thank you for the helpful and thorough response! The links were great. And I appreciated hearing your Personal experience. I think I will do it right, by not planting in the grass, but taking time to rid the grass using black plastic to smother or clear plastic to solarize. And prep the site for seeding. Thanks again!