Improving clay soil

If you live in the Seattle area, it’s inevitable that you’ll run into a patch of heavy clay soil somewhere on your property. The parking strip on the south side of our West Seattle house is mostly clay, and the sole plant that we have out there, a dogwood, doesn’t thrive as well as other plants and trees on our property.

So what do you do if you have clay soil? Whatever you do, don’t add sand to your clay thinking that it will improve the soil. It’s a big no-no and one of the biggest myths.  Sand + clay = cement.

Adding organic matter — such as grass clippings, shredded leaves, composted manure and compost — is one of the best things you can do to improve clay soil conditions. Remaking a landscaping bed is a good time to do it. Dig it into the soil down about 6 to 8 inches deep. Tilling the soil and adding organic matter makes soil more permeable, allowing water to drain. The organic amendments will decompose over time, and help improve the soil structure.

If you’ve got clay soil under your lawn, try aerating the lawn, which pulls core plugs of soil about three inches long and then plug the holes back in with compost.

Some trees and shrubs, however, will do well in clay soils, such as gingko, witch hazel, burning bush, honeysuckle, potentilla, spirea and lilac. When you plant in heavy clay soils, try to plant the trees and shrubs a few inches above the grade of the surrounding soil.

To read more about improving clay soils, click here.