Landscaping Tips for Over and Around the Septic System

Your customers may not want to plant plain and simple grass over the drainfield. Be ready to offer interesting, safe alternatives for groundcover to help protect their systems.

Landscaping Tips for Over and Around the Septic System

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When Scott Chase was approached by a master gardeners group to present a program on landscaping over septic system drainfields, his first thought was, “Sure, I can do that, and the program would just have one slide — grass!” Upon some reflection, however, Chase realized there are lots of other options, and he later prepared and presented a program on planting on and around drainfields. The retired Washington State University Extension program director, who lives on Camano Island, Washington, shared some of those landscaping ideas with Pumper.

Pumper: How did you develop expertise in planting around septic system drainfields?

Chase: I headed up a program for the Washington State University Extension for Island County called Shore Stewards. It was for people who live on the islands (Camano Island and Whidbey Island in Puget Sound, northwest of Seattle) about what practices they could do to ensure that our groundwater and our marine water is protected. Part of that involves septic. That was one of the first things to teach them about. A lot of the people who joined are not from here. They are from a major city like Seattle, or they might have come from another state and never lived with septic before. It was really important to learn about that sort of thing, moving to a rural environment. On Camano Island, where I live, everybody is on septic. I had been teaching classes and doing presentations on bluff stability. A lot of people live on shoreline properties where there are bluffs, and they have to worry about that sort of thing. I had also assisted in doing Septic 101 classes. As far as drainfields are concerned, there are lots of other things to plant besides grass, and some of them are the same native plants that I had always encouraged for bluffs, except just the ones that are shallow-rooted plants.

Pumper: Why do the plants have to be shallow rooted?

Chase: We’re in a temperate climate in western Washington. We don’t really have our ground freeze. Our septic pipes can be as close to the surface as 6 inches. Anything you plant with roots over 6 inches long can get into the drain holes of the pipe and clog things up.

Pumper: Why do you emphasize native plants?

Chase: Once native plants are established, you don’t have to worry about watering them at all. I want to discourage watering over the drainfield. We caution against any irrigation. If you are watering, it ends up saturating the ground above the pipes. You like to have it relatively dry. What comes out of the drainfield itself has to be able to be picked up by the roots of the plants. The drainfield has to be able to go through evapotranspiration. That’s a process by which plants and trees or any kind of foliage or groundcover soaks up the water from the soil and transpires, basically sweats it out into the atmosphere, through their leaves. A large tree like a Douglas fir can transpire up to 100 gallons of water a day, or thousands of gallons over the summer. Short-rooted plants and other groundcovers don’t transpire that much, but they are needed to allow the water, the effluent, to be transpired out as much as possible. The way we look at it, the ground around there is a living, breathing thing. If it is heavy with water, it isn’t allowed to evaporate. That’s what happens if you have a lot of watering. Native plants that are adapted to the area, once they are stable, don’t need watering. They get what they need from the normal rain that we have. We don’t want to add to that.

Pumper: What can be planted over the drainfield besides grass?

Chase: There are meadow mixes of seeds that include a mix of broadleaf and grass species and flowers. Sometimes they are called ecolawns. The different plants in the mix are mutually compatible, need less water and less fertilizer than conventional lawns. They are mowable, but they require less mowing than a conventional lawn. Sometimes they include dwarf perennial ryegrass and hard fescue, clover and alyssum, a small flowering plant.

Pumper: Can trees or bushes be planted near a drainfield?

Chase: Dwarf varieties are better. The advice we give is that the height of what the tree will become is equal to the distance from the drainfield. If it’s going to be 30 feet tall, then 30 feet from the edge of the drainfield is the rule of thumb. Before you plant something like that you might check to see how deep that tree’s root system will grow, which you can usually get from the nursery or find online. 

Pumper: Are there certain things that should never be near a drainfield?

Chase: Willows are ones that you really want to avoid. Any trees that are really attracted to water, like cottonwoods, you really want to avoid planting near a drainfield. Larger grasses, such as pampas grass and bamboo are also bad.

Pumper: What about landscaping right over the tank? 

Chase: There are many options for covering up things that are not as attractive as they could be, like inspection covers. If you do a Google image search ‘hiding septic tank covers,’ you’ll find hundreds of images, ranging from fake rocks to planters that appear to be large, but are mostly hollow below the top portion. All examples are lightweight and easy to move for inspections and pumping. You’ll see circular mosaic pieces that you can place directly over the green riser cover and birdbaths that have a hollow base that can fit directly over PVC septic vents. It’s amazing how many decorative solutions are out there.

Pumper: Any advice for installers and pumpers for talking about landscaping with their clients? 

Chase: It would be a good idea to have a handout they could give to people relevant to their location in the U.S. They could get information from a local nursery if it’s a nursery that specializes in native plants. They might also check with their university extension office or soil conservation district, or the master gardeners program. Most of those would have information relevant to that area. What works for New York doesn’t work for Utah, Florida or California. If the pumper or installer gives them something for maintenance and upkeep, they’ll remember that. It would be a good way to keep the business name in front of the homeowner.  


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