Compost & Clay Soil


Not all yards and gardens are blessed with quality topsoil that is full of the necessary ingredients for optimal plant growth. Often homeowners will find their yard soil to be primarily clay. This can make growing lawns, flowers and vegetables a challenge. Fortunately one simple answer to helping clay soil become much more beneficial to plants is the regular addition of compost to the clay. Compost solves a multitude of clay problems.

Characteristics of Clay Soil

Clay soil is composed of very fine particles that want to clump together in tight bonds. This soil has little space for water to drain through, so it saturates easily and remains so for long periods, which deprives the plant roots of air. It warms slowly in the spring, prevents roots from growing vigorously and is generally hard to work without compacting it even further. Clay soil is often alkaline, which is not good for most garden plants.


Compost is decomposed organic matter that is created by careful management of plant waste. You can buy compost or create it yourself with a home system. Compost is usually made from yard debris, such as grass clippings, leaves and small stems, and kitchen leftovers, like vegetable peelings, eggshells and food past it’s prime. A small amount of animal manure is sometimes added. Mixed together and allowed to decompose, these ingredients turn into a dark, crumbly, sweet-smelling material that can be added to the soil by digging it in or using it for mulch.

Microfauna Nourishment

“Feed the soil, not the plant” is a common expression among experienced gardeners. Billions of microfauna live in each spoonful of well-maintained soil, and many of them are necessary to the good health of plants. The microfauna live off the decaying remains of any organic material in the soil, and the richer the soil, the stronger the population.

Water Management

Because clay soil is dense, it has a problem absorbing water. Rainfall can run off the top without soaking deeply into the soil where the roots are. When it does soak into the soil, it completely fills the air spaces, depriving the plant of necessary oxygen. Compost lightens the clay soil, allowing water to flow more freely through it. It also holds much more water for a longer time than plain soil, so the plants can withstand droughts better. As the microfauna and worms further decompose the compost, air pockets and passages form, which provides oxygen.


How easily the soil is worked is known as friability. Heavy clay soil can almost be like children’s modeling clay–easy to knead when wet but hard as a rock when dry. If it is exposed to the hot summer sun, it becomes a hardened mass of material that can resist the growth of even the most vigorous plants. Compost breaks up that sticky tendency and allows the soil to crumble easily, even when dry.

Alkaline Clay

Clay soil is often more alkaline than many plants prefer. Well-aged compost is much closer to neutral pH. Keeping the clay soil well supplied with compost will eventually change the clay soil to a more neutral environment. As the compost completely decomposes, the soil will turn alkaline again.


Over a period of several years, even the largest amount of organic matter in the soil decomposes and goes away. To keep clay soil most productive, you need to continually and regularly apply compost. A good amount each year would be around 3 inches spread over 100 square feet, or about 1 cubic yard.

Keywords: clay soil compost, amend clay soil, compost helping clay

About this Author

Jack Burton started writing professionally in 1980. He has written for "Word from Jerusalem," "ICEJ Daily News" and Tagalong Garden News. Burton managed radio stations, TV studios and newspapers, and was the chief fundraiser for Taltree Arboretum. He has a Bachelor of Science in broadcasting from John Brown University, and retired from the Navy Reserve in 1999.