Imagine trying to get a breath of air in a room that has none. That is what a plant experiences in soil containing too much clay. Particles of clay are much smaller than those of other types of soil. When they pack together there is no room for anything, including air and water, to penetrate. There are certain plants that will grow in clay soils, such as the daylily and goldenrod, but most plants require a well-draining soil. To achieve that type of texture will require breaking up and amending the clay soil in your garden. Generally, you will need one cubic yard of soil amending material for every 100 square feet of soil.
Cultivate clay soil with a gardening fork and not a shovel, according to information provided by the University of California. This is especially important when working with damp soil. Dig into the existing planting bed, turning the soil and breaking up large clods. Remove any roots, rocks or other debris.
Spread a four inch layer of organic soil amendments such as compost, well-rotted manure, and lawn clippings over the top of the soil. If your soil is particularly compacted, add an inch or two of shredded bark to aid in aeration and drainage.
Use the fork to blend these materials into the top eight inches of the existing soil, mixing it in well.
Spread a two inch layer of wood mulch over the amended soil and level the area with a rake.