Gardening in clay soil presents many challenges. Clay compacts easily, often becoming waterlogged and lacking oxygen. Summer heat can bake it into a surface like cement. There are advantages to the soil type, however. Clay retains nutrients and moisture, and is high in certain trace minerals plants require. According to the University of California, it may take years of careful handling to restore soil structure. Breaking up clay soil is a long and labor-intensive process, but well worth the results. Improving soil quality and drainage will maximize plant growth.
Lay a thick coat of mulch on the garden area in early fall. The mulch can be leaves, straw or compost. Mulch will improve and soften soil texture as it breaks down, making it much easier to work with. Leave this on for at least a year, adding more as needed. Clay soils that have a sandy or loamy base will be greatly improved by this method alone. Pull aside the mulch and check the soil texture every few months.
Dig the area as soon as the soil can be worked in the spring. Use a spading fork on very compacted areas to break up clods. Wait a few days after the initial digging to allow the surface soil to dry, then resume. Shovel deeply, incorporating the mulch and the clay as much as possible.
Use a tiller for places that are too hard for a shovel or fork. Tilling should only be done when the soil is reasonably dry. Pick up a clump of dirt and squeeze it into a ball. If no moisture emerges, it is safe to till. Tilling wet soil will compound the problem of compaction. Go over the area only briefly. The object is to mix the surface mulch within the soil body.
Test the soil to determine nutrient deficiencies. Soil test kits can be purchased at retail garden centers. Nitrogen, potassium or phosphorus may be lacking. Testing will also determine whether the soil is acid or alkaline. Apply amendments such as agricultural lime and bone meal based on the results of the soil test.
Start your vegetable garden immediately in spring. Prepare the seed bed by breaking up clods thoroughly and raking smooth. Small seeds such as carrots and lettuce require fine soil particles to germinate successfully.
Ornamental landscape gardens will need another layer of mulch or compost in spring and fall. Routinely mulching clay soil will keep the soil from drying out and hardening. Plant larger trees and shrubs in autumn as root growth during the winter will break up the subsoil even further.
Dig the last stubborn areas in spring, again mixing the mulch with the subsoil. Plant small shrubs and perennials. By summer of the second year, the overall soil texture will be loose and crumbly. Mulching should occur every year thereafter to maintain soil quality.