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Landscaping when you have an on-site sewage system (OSS) requires special care. Since your yard is where wastewater is treated, a landscape design should not interfere with the natural functioning of your OSS. A balanced combination of oxygen and organisms will maintain healthy soils necessary for your system.

3 easy steps to develop a landscape design:

Search and download a copy of your as-built drawings

An as-built is a drawing of your septic system in relation to your house and property boundaries. Your septic system designer completes the as-built after the septic system is installed. Public Health keeps as-built drawings on file as public information. You can request Public Health to search their records for your septic system. NOTE: Not all records are complete and older septic systems may not have as-builts.

Avoid landscaping on or near the septic tank. Consider installing "risers" or septic tank lids to make septic tank pumping and monitoring visits easier and less time-consuming.

The septic tank, drainfield and reserve area should be clear of:

  • underground sprinkler lines
  • decks, patios, sports courts, or utility storage sheds
  • swingsets
  • sand boxes
  • paved or dirt driveways
  • parked vehicles

After locating the septic tank, drainfield and reserve area, you may now begin the design phase. Keep the tips in Step 2 in mind.

Do's and Don'ts when preparing your garden:

  • Don't plant a vegetable garden on or near the drainfield or reserve area
  • Plants over the septic system may be disturbed or destroyed with repair work
  • Don't put plastic sheets, bark, gravel or other fill over the drainfield or reserve area
  • Don't reshape or fill the ground surface over the drainfield and reserve area (just adding topsoil is generally OK as long as it doesn't exceed a couple of inches over the drainfield area)
  • Grass or the existing native vegetation are the best covers for your drainfield and reserve area
  • Direct all surface drainage areas away from the septic system
  • Use shallow-rooted plants (see plant list below)
  • Avoid water-loving plants and trees
  • Do not make ponds on or near the septic system and the reserve area

Suggested plant list (provided by Washington Sea Grant Program):


Groundcovers for sun:

Groundcovers for shade: