Clay soil is a problem in the garden when growing vegetables, trees, or foliage. Clay compacts easily and can become waterlogged. This leaves little room for oxygen to get to the plant roots, causing rot and other plant diseases if the soil is not treated before planting. Treating clay soil requires the addition of organic fillers to restore structure to the soil so your plants can grow and receive the needed oxygen and moisture content to remain healthy and thrive.
Till hard clay soil with a spading fork to break up large clods and help expose the soil to the sun and air. Turn the soil over with your spade, digging as far down as 8 inches and working in small areas at a time to break up the clay.
Leave larger clay clods that are resistant to breakage on the top of the soil to dry out in the sun.
Wet the clay clods with water after they have dried and break up the remaining clods with a steel garden rake.
Add green plant materials, compost, sand and animal manure, up to one half of the soil content, mixing it into the clay earth. When using manure, leach out excessive salts in the manure by running water through it before adding it to the clay.
Avoid using organic materials that decay slowly over time such as sawdust, straw and peat moss, as they will use extra nitrogen needed by the plants for growth. If this is your only available medium, you may need to add additional nitrogen into the soil to compensate if you are planning to plant right away.
Add gypsum to the soil if you have sodic (acidic) soil. You can usually tell these types of soils by the hard crust that forms on the top of earth after a good rain. Apply a top layer of gypsum (5 pounds to every 100 square feet) to the soil after it has been worked with the other organic materials.