Clay soil is a dense type of soil. It is non-porous, making it difficult for plants to grow. The dense nature of clay soil can impede the ability of plants to absorb nutrients, and may drown the roots of a plant as water collects. Modify clay soil using tools and additives to break up compaction, and enrich clay soil with organic material to improve its ability to nurture a variety of garden plants.
Break up the soil using a hoe or hand shovel to prepare the clay for the gypsum lime. Gypsum, or calcium sulfate, is a garden additive that will not raise the soil's pH level, while potentially improving soil quality--particularly soils that are alkaline.
Apply gypsum to your soil at a rate of 40 pounds per 1,000 square feet of soil.
Mix the gypsum into the soil and water it well. Allow the gypsum to absorb into the soil, which may take several hours. You begin to see the soil break apart and the moisture absorb into the soil when the gypsum is absorbed. Several applications may be necessary to see a permanent change in the soil.
Add organic matter such as manure, compost, or peat into the soil. Wood chips provide aeration to the soil, allowing water to drain while maintaining a small amount for plant roots. Bark or straw are also used to make clay porous, and helps keep large, compacted chunks from forming. Material such as vermiculite should be avoided for its high water retention. Mix in at least a 1-inch layer of organic material to improve soil quality.
Choose plants suited to growing in clay soil. While working to improve your soil, don't fight it. There are any number of ornamental flowering plants as well as shrubs and trees that will grow in clay soil. According to the Missouri Botanical Garden's Kemper Center for Home Gardening, annuals like marigolds and dianthus, perennials like black-eyed susans and mealycup sage, and bulbs like daffodils and crocus are all well suited to growing in clay soil. The center also notes that many ornamental grasses and needled-evergreen shrubs grow well in clay.