How to Amend Clay Soils


Clay soil can be a difficult type of soil for gardening. Because of the size of the soil particles, clay soil clumps together with very little space between each particle. This prevents water from draining easily from the soil. As a result, clay soil is often sticky and damp in spring and rock-hard in summer. Plants placed in heavy clay soil may not grow well because the clay will stunt the growth of the roots and hold water, which will promote root rot. The best way to improve clay soil is to add organic soil amendments.

Step 1

Collect soil samples in fall by digging 1 quart of soil from each soil sampling location and placing it in a bucket. Collect up to 10 soil samples across your property. Remove debris such as roots, plant matter, sticks and rocks. Mix the soil and allow it to dry. Place 1 cup of soil in a plastic bag and take it to your local county extension service. For a nominal fee, your county extension service will send the soil to the nearest agricultural university-run soil laboratory for testing. Test results will indicate which amendments will best improve your clay soil. These results are typically returned within three weeks.

Step 2

Break up your clay soil after the soil has thawed and dried in spring with a rototiller. Breaking up wet clay soil will further compact the soil and cause it to dry into rock-hard clumps. Break up the soil to a depth of 12 inches.

Step 3

Spread soil amendments that were recommended by the soil test over your soil in a 4-inch layer. Good soil amendments for clay soil include organic substances such as compost, peat moss, wood chips, manure, grass clippings, straw and sawdust. Irregularly shaped amendments such as wood chips will incorporate air into the soil to speed drainage, while nutrient-rich material such as compost will help to build nutrients into poor soil.

Step 4

Mix the amendments into the soil with the rototiller.

Things You'll Need

  • Shovel
  • Plastic bucket
  • Plastic bag
  • Rototiller
  • Compost
  • Peat moss
  • Wood chips
  • Manure
  • Grass clippings
  • Straw and sawdust


  • Washington State University Extension: Soil Management for In-ground Nursery Crops
  • Oregon State University Extension:Improving Garden Soils with Organic Matter
  • University of Minnesota Extension: Soil Compaction Causes and Consequences

Who Can Help

  • Colorado State University Extension: Choosing a Soil Amendment
Keywords: amending soil, improving clay soil, changing soil structure

About this Author

Tracy S. Morris has been a freelance writer since 2000. She has published two novels and numerous online articles. Her work has appeared in national magazines and newspapers, including "Ferrets," "CatFancy," "Lexington Herald Leader" and "The Tulsa World."