Healthy, fertile soil is a mixture of water, air, minerals, and organic matter. In soil, organic matter consists of plant and animal material that is in the process of decomposing. When it has fully decomposed it is called humus. This humus is important for soil structure because it holds individual mineral particles together in clusters. Ideal soil has a granular, crumbly structure that allows water to drain through it, and allows oxygen and carbon dioxide to move freely between spaces within the soil and the air above.
Successful gardening depends on good soil.
One of the best ways to improve soil fertility is to add organic matter. It helps soil hold important plant nutrients. By adding organic matter to sandy soil, you improve the ability of the soil to retain water. In a clay soil, humus will loosen the soil to make it more crumbly. You can increase the organic matter in your garden by adding compost or applying mulch.