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How to Compost for Clay Soil

By Contributing Writer ; Updated September 21, 2017

If you squeeze a handful of soil and the shape holds like modeling clay purchased from a hobby store, you have clay soil. Clay soils look pale compared to the rich, chocolate brown topsoils in gardening stores because they lack adequate organic matter, like carbon, and nutrients, like nitrogen. But there is no need to give up gardening or to buy expensive topsoil if you have clay. Create healthier dirt through composting. It’s like improving any soil, except it requires more growing seasons and a higher concentration of compost.

Decide if you will purchase or build a bin. All have lids and ventilation holes but vary in the volume of compost they can hold and in how easy it is to stir, or turn, the materials inside. Construct a bin by punching ventilation holes in a plastic storage container. Or construct an enclosure in your yard using interlocking landscape bricks to create walls 2 feet high.

Choose a sunny location for your compost heap, and fill the compost bin or enclosure with organic materials. Add alternating layers of dark (leaves or paper) and green materials (lawn clippings and vegetable scraps). Compost should contain at least twice as much dark materials than green. In an open, brick enclosure, add a top layer of one to two inches of leaves; they will minimize flies and discourage animals from scavenging.

Add earthworms to the bin. Collect specimens from your yard that live in the upper six inches of soil. If you have an enclosed bin, add about 1 cup of earthworms for 3 cubic feet of compost. If you have an enclosure, dig into the center of the heap after one week and check for worms; compacted clay soil may lack an adequate supply of worms to crawl into the compost.

Keep the compost heap moist but never soggy. Water to benefit worms and bacterial processes when dry and turn with the shovel to aerate when wet. Too much water will cause rotting odors and may attract fruit flies and pill bugs.

Add material to your compost for the entire growing season. Water during the winter if needed. You will have soil the following spring.

Work a layer of three to four inches of compost into the top two or three inches of your clay soil In the spring. Clay will not begin to break down if your ratio of compost to clay is too low. You will see improvements in the color and texture of your clay soil after four to five seasons of adding compost.


Things You Will Need

  • Leaves, dry grass, paper strips or cardboard
  • Fruits, vegetables or fresh lawn clippings
  • Container or bin
  • Earthworms
  • Shovel with a 3- to 5-foot handle


  • Do not be concerned if your compost releases steam; the center of an active compost heap can rise to more than 100 degrees Fahrenheit because of natural bacterial processes.
  • Beginners should use a compost container of 3 by 3 feet. This holds the minimum, recommended volume to keep composting bacteria and worms alive.
  • Red worms (Eisenia foetida) are popular for composting because, according to the Washington State Cooperative Extension, 1 lb. of the worms can consume .5 lb. of vegetation per day. They can die, however, if temperatures in the compost rise above the upper 80s or fall below freezing. You may need to overwinter red worms in trays in your home.


  • Never add animal products, pet waste or grease to your compost.