The Best Soil to Spread Over Hard Clay Soil

Goal

• The particles in clay soil are small and packed tightly together, and water passes slowly through them if at all. The goal is to transform an uncooperative medium into one that is loose, rich and considerate of whatever will grow there. Simply placing new soil on top of old hard clay eventually enriches and makes it more friable, but working it into the clay yields results a lot sooner. The best soil, or medium, to apply on top of hard-packed clay is a well-balanced organic material, ideally in the form of compost or well-rotted manure.

Types of Soil

• Soil falls into two basic categories based on their makeup: sandy and clay. Sand particles are large, create large spaces between them, and dry out quickly in the heat. Clay, as well as silt, particles are smaller and are packed more tightly together, resulting in heavy soil. Clay soils warm more slowly in spring and are much harder to work than sandy soils. Adding organic matter, such as manure or compost, conditions the soil and eventually imparts its properties to the clay. Regular yearly additions of organic materials improve not only the soil's ability to drain water but also its capacity to store nutrients needed by plants.

Joining Forces

• On its own, sand does not hold together, while clay holds together too well. Adding sand to clay may help, but only if it is combined with a generous amount of organic matter. Sand alone only causes clay to compact even more tightly. The Oregon State University Extension Service states that while sand can make clay soil more workable, it should only added following the addition of organic matter. The extension recommends 2 inches of sand and 2 inches of organic matter to improve the texture of hard clay soil.

Considerations

• Although new soil can simply be spread over clay, working the new materials into the original soil results in better soil faster. Improving hard clay involves digging it down to about 12 inches, spreading about 3 inches of manure or compost on top, and working it in thoroughly. While it takes some time for the nutrients and minerals to incorporate themselves into the clay, the improvement in its texture and workability is immediately evident. Covering the newly amended clay soil with an additional 2 to 3 inches of wood mulch or pine bark helps reduce weeds, and the bark's decomposition adds even more nutrients to the soil.