The Drainfield Garden (nicknamed the Toto Garden) was originally established as an experimental garden to test the root invasiveness of plants that were commonly recommended for growing on a drainfield. Master Gardener Marcia Nelson started the project to test the assumption that selected plants had non-invasive roots, using a mock drainfield.
A mound is a type of drainfield that is installed when the ground does not percolate at required county standards. The mound in the drainfield garden is evolving to display plantings that consider current knowledge of best practices for plants to use in drainfields.
General guidelines for drainfields:
- No playgrounds, patios, irrigation systems, or mulch, since these interfere with septic evaporation. Playgrounds compact the soil.
- No trees or large shrubs, since large root systems will interfere with conduits. Beware of trees planted close to or within the drip line of a drainfield.
- No edible plants, since fruits, berries, herbs, and vegetables require too much water and tilling. Also, plants on drainfields may be contaminated with harmful organisms.
- Use gloves whenever working with soil or plants on a drainfield.
The following free downloads provide useful information about best practices for drainfield planting:
- Planting over a Septic System, Community Horticulture Fact Sheet #98, Washington State University, Snohomish County Extension
- Landscaping Your Septic System, by Teri King and Jodie Holdcroft, Sea Grant Washington
- Drainfield Landscaping Suggestions: Shallow Rooted Plants, Clallam County Environmental Health Services
- Landscaping Your Drainfield, Thurston County Public Health and Social Services, Environmental Health Division