Amending Clay Soil for a Vegetable Garden

Clay Soil Definition

• Clay soil particles are the smallest and the most tightly bound together. Each tiny, multifaceted particle joins easily to the others around it, making for a very tight seal through which water passes at the proverbial snail's pace. It can take up to 200 years for water to pass completely through a layer of clay that is roughly 3 feet deep. But just as clay clings to water, it also clings to other substances, including the minerals and nutrients that plants need to grow. As difficult as it is to work with, clay soil isn't the gardening bane that many think it is, as it is actually packed with nutrients. It's simply a matter of getting those nutrients, as well as the medium they exist in, to loosen up a bit, and amending it with various materials does just this.

Preparing the Bed

• Before adding amendments, unbroken clay soil must be turned over and allowed to dry. This begins the loosening process, as it exposes the tightly bound damp soil particles to sunlight and air and encourages microbial activity. Next come the organic materials, which include compost, aged manure, grass clippings, shredded leaves and sawdust, which not only improve the texture of clay soil but boost its nutritional content as well. These should be incorporated into at least the first top 10 inches of soil, creating a loose subsoil that is receptive to the tender new vegetable plant roots. Don't expect quick results, particularly if you're planning a vegetable garden in new soil that has never been tilled before. But the rewards of working in lots of compost and manure make it worth the wait.

Cover Crops and Mulches

• Serious vegetable gardeners often use cover crops to amend clay soil. Rye, crimson clover, oats and hairy vetch are examples of green manure that is planted in garden beds in the fall and tilled under in the spring. While mulches are not considered amendments, many eventually become just that, as in the case of mulch hay that decomposes into the soil once it ceases to be effective in preventing weed growth and water runoff.

Considerations

• Vermiculite, perlite, pea gravel, sand and tire chunks are examples of inorganic soil amendments. While they aerate dense clay soils and improve water permeability, they do nothing from a nutritional standpoint, as they do not decompose. They simply push their way in between tiny clay soil particles and keep them separate, allowing water and air to pass through more efficiently. No matter what clay soil amendments you use, they should be thoroughly mixed into the soil rather than merely placed on top or buried, as materials that are improperly applied may interfere with water and air absorption as well as root development.