Clay soil offers many problems to gardeners. It is water retentive, drains slowly and compacts to rock form when dried. Because of these issues, many plants cannot be safely grown in clay soil. Cacti rot and weak rooted plants cannot spread through the rock like soil. There is hope for gardeners with clay soil. This heavy substance can be broken up and made into a lighter growing medium with only a few supplies.
Choose a dry day when the soil is not too dry or wet. Remove all large debris and rocks from the area. Dig out stumps and roots with the shovel. Till the area thoroughly as deeply as possible. It may take several runs. With the tiller set on the highest setting, make one pass through the area. For each additional tilling, set the blades lower, until the last pass is at the lowest setting. Rake the area level, and check for large masses of clay. Break the clods of soil up with the shovel and rake.
Spread a thick layer of compost on the entire area to be amended. Till this layer in well. Broadcast the bark mulch and fertilizer evenly across the clay before tilling it in. Till this mixture until the organic matter is evenly distributed throughout the soil. If the soil needs acidifying, apply cottonseed meal as per the manufacturer's recommended dosage. Break up any large clumps found, and rake them level with the soil.
Wet a patch of soil and squeeze it between your hands. It should form a ball that holds together but is easily broken up. If when the wet soil is squeezed it feels like paste and is hard to break up, add and till in additional organic matter.