What Should You Plant Over the Septic System?

Landscape designer Wynn Nielsen shares her top tips for drainfield ground cover and the “badass’’ list of plants homeowners should avoid at all costs.
What Should You Plant Over the Septic System?
Shown here are creeping phlox, dwarf boxwood, hebe, thyme and iris, which would be considered safe to plant over the septic field.

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Making your daily pumping rounds, you’ve witnessed the myriad of ways homeowners sabotage their septic systems through poor landscaping or other uninformed land-use choices. When the driveway is crowded, they park cars over the septic system. They construct a wooden deck over the septic tank, hindering your access. They plant a water-hungry weeping willow tree next to the drainfield.

They invite root intrusion, soil compaction and broken and damaged drainlines, and then wonder why they’re having problems maintaining the septic system. You patiently share the do’s and don’ts of caring for a septic system and wish someone was out there to educate these homeowners before they make mistakes in the backyard that lead to costly repairs or replacement of the septic system.

Enter Wynn Nielsen, a landscape/garden designer on Bowen Island, a 20-minute ferry ride from Vancouver, British Columbia, Canada. To help frustrated property owners – who don’t understand how their septic system works or maybe don’t even know they have a septic system – Nielsen recently created a presentation about landscaping around the septic system. She teamed with Scott Stevenson, owner of Bowen Island Septic Services, for a talk with 60 local gardeners.

Landscaping designers are typically late to the game when properties are being developed, Nielsen says, when homeowners already have preconceived notions about how they want to utilize their lots. Unfortunately, Nielsen often has to shoot down those notions.

“Septic fields tend to occupy the most desirable areas of the lot and people tend to want to use them,’’ she explains. “People want to put patios and decks and hot tubs there. They want to create soccer fields and grow vegetables. I’m the one who has to come in with the bad news that you can’t do that without damaging the septic field.

“There’s a lack of education out there about septic fields,’’ she continues. “Having more awareness of the end-user would be great.’’

Most pumpers are getting ready to kick off the busy season. You’ll surely confront homeowners with little understanding of proper landscaping around the septic system. Bits and pieces of Nielsen’s presentation may help you explain how each planting decision can impact the effective use and longevity of a customer’s septic system. And Nielsen has another bit of advice for the septic pumpers and installers: When homeowners have a lot of questions and concerns about their landscaping, don’t be afraid to call in a professional designer.

STEER CLEAR OF THESE

You’re familiar with the first rule of planting around the septic system: Avoid thirsty plants that set deep roots. Nielsen tells homeowners to keep a distance for water-loving trees that include willows, birch, silver maple, elm, beech, walnut and linden. She cautions against planting aggressive, dense ground covers that will interfere with the evaporation process, including pachysandra, cotoneaster and periwinkle. Other plants to avoid for their aggressive roots are vines, wisteria, bittersweet, morning glory, campsis and hops.

Nielsen has developed a general “badass’’ list of plants to avoid near the septic system:

  • Bamboo (any variety)
  • Any trees with particularly strong lateral root growth
  • Water-loving, large-scale pond grasses
  • Native clematis (self seeding)
  • Cedars (except genetic dwarfs)
  • Woody vines

Prairie grasses and meadows can be no-mow and restrict traffic over the septic fields, which are good things, so people think they are desirable. But Nielsen says these are often unwise choices for the septic field. “Prairie grasses and perennials have some of the longest, tangliest, toughest roots around,’’ she says. The drought-resistant nature of prairie grasses translates to aggressive roots adept at seeking out water sources like perforated drainpipes.

Cedar trees and shrubs — evergreens perfect for many screening situations — are a favorite of homeowners, but they are also a no-no, Nielsen says.

“Cedars are wonderful, but they are a problem next to the septic field. Either you’re going to have a short-lived septic field or you’re going to cut those roots on a regular basis,’’ she says.

In general, it’s better to choose trees with vertical root growth if you want to plant near the septic field. When homeowners insist on planting trees with strong lateral root growth, tell them to back off.

“The rule of thumb is to keep a distance equal to the anticipated height of the tree at its maturity, plus 20 percent. Thus, a tree 30 feet tall at maturity should be kept 36 feet away from your septic field,” Nielsen recommends.

Those who want landscape-intensive yards also have to be warned not to plant vegetables over the septic field. Nielsen said some clients insist the drainfield, with its nutrient-laden effluent dispersal, makes a perfect spot for vegetables. But she warns them that disturbing the soil with these annual crops is bad for the septic system, and the effluent could transmit pathogens to the edibles.

GO AHEAD AND PLANT THESE

While traditional lawns are acceptable over septic systems, Nielsen says many homeowners are moving away from that maintenance-heavy chemical input and water-intense ground cover. She points to a few grass varieties that are generally better than others. Safer choices may include:

  • Pre-mixed eco-grass with fescues
  • Small grasses, including tufted fescues, feather grass, pennisetum, deschampsia
  • Grass-like choices, including mondo grass, liatris, liriope, armeria

“Lawns are not very ecologically friendly. They don’t make good habitat for most things, but we still have children and dogs and they provide great places to run around on,’’ she says.

Rather than traditional lawns, Nielsen recommends drought-tolerant plants with short, fibrous root systems chosen for hardiness in your climate and in sun and shade conditions as required. Her list of top choices includes microclover/ecograss/carex pensylvanica dwarf, introduction of white clover, carpets (thyme, sedums, low-growing ground covers), shallow, short/soft rooted perennials, bulb/corm/rhizome/tubers in lawns, and moss.

Microclover, she says, is the “weed we used to eradicate in our lawns,’’ and that the “old enemy is now your best friend.’’ It’s low- or no-mow and deer and bees love it.

Other good choices to add landscape interest without placing a septic system at risk are interspersing annuals or bulbs in the ground cover, Nielsen says. Those include hardy cyclamen, crocus, narcissus/daffodils, snowdrop, alliums and anemones. And newer dwarf tree and shrub varieties are also not the same threat as their bigger siblings. They include cedars, cherry, crabapples, dogwoods, cotinus, cercis, snowbell, acer palmatum, acer grisem and acer amur. Shrubs with fibrous root systems include boxwood, potentilla, daphne, choisya, hebe and euonymous.

CONSIDER LAND USAGE

Typically, homeowners hire Nielsen to draw a landscaping plan after a site has been developed and a home has been built. But ideally, developers and septic installers would involve a landscape designer earlier in the process to result in the best usage of the property, Nielsen says.

Often the lot clearly dictates one location for the septic field, and it’s usually the flattest, sunniest area that is also the spot best suited for intensive gardening, according to Nielsen.

Sometimes the lot leaves little choice to move the drainfield, but often changes can be made in the planning stage to allow better placement for the homeowner.

“Sometimes their ability to use property they paid a lot of money for is really inhibited by these decisions and it’s sad,’’ Nielsen says. “People developing the land put (the septic system) in the most convenient, accessible place. They’re not thinking about how the homeowner is going to want to use the property. A little more up-front thinking would make my job a lot easier.’’

Through her landscaping presentation and getting to know pumping professionals on Bowen Island, Nielsen is looking to educate homeowners and maybe save a few septic systems in the process.



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