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Landscaping with an on-site sewage system

Learn about the special needs of lanscaping with a septic system.

OSS rule revision process

Recently, the Washington State Board of health approved changes to statewide OSS rules. Now, King County is updating our local codes to make sure they comply with the state’s changes.

Stay informed by signing up for our code revision newsletter. You can also read our June edition.

Landscaping when you have a septic system requires special care. Your yard is where sewage is treated, so a landscape design should not interfere with the natural functioning of your septic system.

A balanced combination of oxygen and organisms will maintain the healthy soils necessary for your system.

3 easy steps to landscape design

  • Search and download a copy of your record drawings.

    A record drawing is a drawing of your septic system in relation to your house and property boundaries. Your septic system designer completes the record drawing after the septic system is installed.

    Public Health - Seattle & King County keeps record drawings on file as public information. You can search for your record drawing online or request Public Health - Seattle & King County to search their records for your septic system.

    Note: Not all records are complete, and older septic systems may not have record drawings.

  • Locate the septic tank, drainfield, and reserve area using the landscape design.

    Avoid landscaping on or near the septic tank. Consider installing "risers" or septic tank lids. This will 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
    • Swing sets
    • Sand boxes
    • Paved or dirt driveways
    • Parked vehicles
  • Begin the landscape design.

    After locating the septic tank, drainfield and reserve area, you may now begin the design phase.

    Keep the tips in Step 2 in mind.

Tips for 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 (adding topsoil is generally okay as long as it doesn't exceed 2 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:


  • Fescue
  • Lawn
  • Ornamental grasses
  • Wildflower meadow mixes

Groundcovers for sun:

  • Bugleweed (Ajuga)
  • Carpet heathers (Calluna)
  • Cotoneaster (Cotoneaster)
  • Ground Ivy (Glechonma)
  • Kinnickinick (Arctostapylos)
  • Periwinkle (Vinca)
  • Soapwort (Saponaria)

Groundcovers for shade:

  • Bunchberry (Cornus)
  • Chameleon (Houtuynnia)
  • Ferns
  • Mosses
  • Sweet Woodruff (Galium)
  • Wild Ginger (Asarum)
  • Wintergreen (Gaultheria)

List provided by the Washington Sea Grant Program.