The Properties of Clay Soil

Growing most plants and crops in clay soil can be a difficult task. Problems such as water-logging are common and can cause of root rot in many plants. However, with the proper treatment and amendments, you can modify clay soil to successfully cultivate your own garden.


Clay is made up of minuscule particles that form a hard, concrete-like consistency when dry, and a sticky mixture when wet. In general, soil is composed of sand, clay and silt particles. If your soil is comprised of more than 40 percent clay, it can be classified as clay soil. You can assess the clay content in your soil with a simple test. Take a small amount of soil in your hand and mix with some water to form a dough-like consistency. Press the dough in your palms and try to flatten it. Crumbly soil with more sand and silt with fall apart easily. Clay soil, on the other hand can be stretched almost to the length of your palm. The more the dough stretches, the higher the clay content in the soil.

Water Retention

Because of the composition of clay soil, it holds together very well to form a compact mass. Water retention is quite high and can result in problems such as water-logging and root infections for plants. The roots of plants may also find it difficult to travel through the soil because of the rigid structure.

Nutrient Retention

Clay is composed of particles that have a negative charge on them. This enables the soil to attract and hold on to mineral nutrients that are positive in charge. Some of the nutrients such as magnesium, potassium and calcium are vital to the growth of healthy plants. Good nutrient retention is one of the positive qualities of clay soil.

Difficult to Cultivate

Clay coil can be difficult to dig a spade or shovel into because of the hard structure of dry soil. Cultivating wet clay soil will only compound the problem, because it will form tough little clumps that can be hard to take apart.

Low Tilth

Tilth refers to the ease with which a soil can be tilled. In addition, the soil must retain the required amount of water, provide good aeration and promote nutrient absorption. Because of the hardness and compact structure of clay soils, tilth is typically poor. However, with the addition of organic matter such as compost and manure, soil structure and tilth can be greatly improved.

Additional Characteristics

Clay soil is also subject to formation of cracks when it is dry. This can harm the roots of plants, and result in tears. Formation of crusts in dry soil prevents seedlings from emerging, and also blocks roots. In cold weather, clay soils are more prone to heaving, where the plants are pushed out of the soil due to alternate freezing and thawing. Clay soil is also easily compacted with minimal force, which can cause further blockage for roots and seedlings. Clay soils are slow to warm, which can result in a delay in planting time during the spring. Clay soils also tend to be alkaline, and can be modified with sulfur to increase acidity.