The Properties of Sandy Soils

The texture of soil is determined primarily by the size of the mineral particles that make up the soil. The largest of the primary types of soil particles is sand, which ranges between 0.05 and 2 millimeters in diameter. Silt particles are smaller than sand particles, ranging between 0.002 and 0.05 millimeters in diameter. Clay particles are the smallest of all, at less than 0.002 millimeters in diameter.

Soils that are more than 50 percent sand particles are considered to be "sandy soils." Soils made up of more than 80 percent sand are simply referred to as "sand." Sandy soils tend to be easier to work than clay soils, and sandy soils are well-aerated, which helps to keep plants' roots healthy.

Sandy soils are less able to hold water than clay soils. Because of their relatively large size, sand particles tend to fit loosely together in soil, with relatively large spaces between them. Water drains easily through these large spaces and does not stay in the soil for long. In contrast, clay particles are much smaller and fit together more tightly in soil. So they're more resistant to the force of gravity that pulls water quickly through sandy soil.

Clay particles also have more small pores on their surfaces than sand particles do, and water is able to fill these very small spaces. Capillary action exerts a strong hold on the water in these tiny pores, and so the water remains in the soil until drawn out by plants' roots.

Organic matter is an important component of garden soil. Organic materials hold onto moisture and, therefore, help to maintain a consistent moisture level in the soil, which is beneficial to plants. Organic matter loosens the texture of the soil and makes it more conducive to good root development. Organic material also contributes nutrients to the soil as it decomposes.

In general, sandy soils are less able to hold organic matter than are clay soils or other denser soils. Clay particles are able to attach themselves electrochemically to organic materials in a way that sand particles can't. So organic matter is bound in clay soil more firmly than it is in sandy soil. The relatively quick flow of air and water through sandy soil also encourages decomposition, and so organic material breaks down faster in a sandy soil than it does in clay soil.

The ability of clay particles to hold onto organic material electrochemically also allows clay to hold onto chemical nutrients in the soil. The retention of these nutrients is crucial to plant development.

Organic material alone also can hold onto nutrients electrochemically, and because clay soils are better able to hold onto organic matter than sandy soils are, the advantage of clay over sand in terms of nutrient-retention ability is enhanced even further.

One of the most effective ways to improve sandy soil is to add organic material to the soil. The organic material improves the soil's water and nutrient retention capabilities, contributes nutrients to the soil and maintains a soil texture that encourages plants' root development.