To improve clay soil and make it easier to work, add coarse sand and organic matter; such as, humus, compost, manure or leaf mold. The biggest problem with clay soil is that it packs tightly together, and can be difficult to dig in, and impossible for all but the most determined roots to penetrate.
TIP: Our expert gardening advisor, Karen Thurber adds, "Changing the texture of clay soil requires large quantities and repeat applications of soil conditioners. Over time with good soil management the soils work-ability or 'tilth' will improve."
Step 1 - Calculate Sand and Humus
The rule of thumb for applying compost to soil is to use 1 cubic yard for every 100 square feet of soil treated. For sand, how much to add depends on the graininess you want to create. Using 1 cubic yard per 100 square feet is typical, but you can increase the sand as desired. The more sand added, the lower the density of the soil will be.
Step 2 - Aerate Packed Clay
Turn the clay soil to be treated. If you are simply looking to loosen up the soil temporarily, you can skip the additives and simply turn the soil well with a tiller or potato rake. Otherwise, turning the soil will break up the clumps of clay, making it easier to mix in the other ingredients.
Step 3 - Add Compost for Plant Nutrition and Improved Soil Structure
Compost is rich in plant nutrients. Spreading compost on the treated area before tilling the sand into the soil helps make the soil more fertile. Additionally, compost contains many types of bacteria and other microbes that serve the dual purpose of aiding decomposition of plant waste and preventing many unwanted types of parasites and plant disease from getting established. Healthy soil is the most effective way to combat plant disease and parasites, and many experts will tell you that the soil is the first thing to check if you are having problems with plant growth.
TIP: Karen notes, "Add organic matter to the soil before adding sand to avoid creating cement-like soil."
Step 4 - Add Sand for Aeration
Adding sand into clay soil increases the graininess of the soil. The reason the clay clumps together is because the particles are tiny, and naturally stick together. Sand introduces larger, rough grains into the mix, and the clay is not able to bond to itself as uniformly as before. This in turn creates spaces between the grains of the soil, which allows water and nutrients to be transported to the roots of plants.
Benefits of Clay Soil
Soil with a high clay content is denser than other soil types, making it able to retain moisture in drier weather. It is also a more stable type of soil, which means it can provide support for larger plants, like bushes or trees. And the most important benefit of all is that clay is high in minerals and trace metals that plants require for optimum growth. Without the compounds that make up clay, soil may become depleted of iron, or even calcium, making it difficult for plants to grow properly.