If you are trying to grow a garden with clay soil, then you have got your work cut out for you. The properties of clay soil are distinctive, and even a child can learn how the clay soil is different from compost, hummus or other types of soil. Clay soil responds differently to water, has a unique texture and affects the roots of garden plants in a way that other kinds of soil do not. If clay soil is troubling you, then getting to the root of the problem and understanding how to amend the soil will make a big difference.
Clay soil has a distinctive texture. When dry, it holds its shape, and does not crumble like sand. When it is wet, it can be sculpted and molded into different shapes. To test the amount of clay in your soil, roll a moist chunk into a 1-inch ball and press it flat between your thumbs. If it falls apart, then you probably do not have much clay content. If it stays together and grows over an inch long before it breaks, then you have a lot of clay content. Most soils will fall somewhere in between, stretching to an inch or so before falling apart. Damp clay soil is very sticky.
In perfect garden soil, there is a mixture of sandy particles, with clay particles, with decomposed organic matter. In clay-rich soil, there is little organic matter. It is the organic matter that supplies nutrients and allows the roots of the plant to climb through the soil with little resistance. Since clay particles are so close together, it can be difficult for roots to travel through the soil. The clay, however, is rich in minerals and its "stickiness" prevents erosion. Adding organic matter (compost) to the soil year after year will eventually result in an improvement for clay soil.
Clay soil can hold a lot of water. Some of the mineral particles swell up when they get wet. This can "choke" tender roots. It also results in a very compacted soil when teeny tiny particles are pressed into one another and then swell up again. If you have soaked your garden thoroughly for two hours or more, and the soil is still dry 2 to 3 inches from the surface, then you probably have a lot of clay in the top layers.
Acidity and Alkalinity
Clay soil tends to be very alkaline. Some plants and insects thrive in an alkaline environment. Others prefer an acidic environment. Most creatures, however, prefer neutrality. The ideal garden soil is fairly neutral at 3-8 on the pH scale. Adding peat moss, composted oak leaves, elemental sulfur, watering with vinegar, cottonseed meal, ammonium phosphate and gypsum can all acidify the soil.
The minerals and moisture-retaining qualities of a heavy amount of clay in soil can be a benefit. When high-clay soil is combined with other types of soils, it can be one of the best compounds for a vegetable or flower garden. The hardest part is just reaching the perfect amount of organic material since the clay soil tends to overpower the organic material.