Sunny Prairie: Native Plants on a Cottage Septic Bed

Your cottage septic leach bed can become wonderful native plant gardens. You just have to choose the right species.

Our clients had a septic system newly installed and wanted the ground covered with native plants over the septic leach bed and surrounding area. The idea was to create a beautiful landscape that didn’t require much maintenance in the form of mowing. As the leach bed was raised and quite prominent, it was important that it looked good, avoiding weeds and the hard work of keeping grass trimmed.

There are special considerations when planting on septic leach beds. While having vegetation on a leach bed is important to help the septic system function well, it is also important to avoid plants that will damage the system.

As a rule of thumb, it is important to choose plants that don’t have deep roots, that are comfortable with dry conditions, and that don’t form a dense mat of foliage.

Here are two good articles that discuss planting on septic leach beds.

From Cottage Life, written by a well-known expert: https://cottagelife.com/outdoors/the-natural-garden-the-wild-bunch/
From Michigan State University: https://www.canr.msu.edu/news/could-you-please-tell-me-what-native-plants-i-can-plant-on-the-drain-field

On top of that, it is important to consider the site conditions. Many leach beds have sunny conditions – this one did. But others might be in part-shade, depending on their orientation and nearby tree canopy.

We wanted to cover the ground quickly, to avoid weed pressure, particularly in the the first year. This was particularly acute do a large population of dandelions on a neighbouring property.

Groundcover layer

Grounded chose the following plants for the groundcover layer.

In addition, we seeded the entire site with an annual flower: Plains Coreopsis (Coreopsis tinctoria). This plant isn’t strictly native to the area, but as it’s an annual, which will fade out in a couple of years, it’s a rule I’m prepared to break for the groundcover benefits it brings.

Vignette layer

For the Vignette layer, we chose plants that would give interest at various times of the year.

A couple of these plants have longer taproots, so they were planted away from the actual leach bed, on the surrounding landscape and the slopes away from the bed.

Because we were planting on a leach bed, there was no structure layer of shrubs. The roots of shrubs go too deep for use on these types of sites.

The design

I divided the site into approximately 10 ft square blocks. Each block had more or less the same plants in it, in an arrangement that suited the growing habits of the plants. Here is what a block looked like: the circles are different species of plants in the vignette layer, the blocks are various groundcover plants.

A graphic showing the layout of plants for the prairie-style garden.

This garden will take a couple of years to fill out. The first summer will require some watering, depending on the weather, while making sure not to overwater for the sake of the plants and the septic bed.

There will also be some weeding required, depending on the performance of the annual plants sowed.

By year three, the ground should be covered and require very little management.

Haliburton native plant prairie style garden, prior to planting. — After installation of the septic system, the installer added topsoil ready for planting.

beginning installation of plants on a septic leach bed — We lay out the plants before we put them in the ground to make sure they are spaced well.

septic leach bed planted with native plants in haliburton county — The plants were placed closer than 12 inches apart to maximize groundcover.

Update: July 2024

I visited this garden a month after it was installed. It grew like gangbusters. This isn’t typical – each garden is different. The rain and sun mix, together with the clients’ diligent weeding, are getting the garden off to a great start.