By amending the soil in your garden, you can improve basic soil structure and, as a result, improve other characteristics of your garden soil. A soil amendment is a material that primarily improves the soil physically, as opposed to chemically. Soil amendments typically consist of organic matter such as peat moss, compost, aged manure, leaf mold, worm castings, or similar organic materials. Although soil amendments sometimes contain plant nutrients, the nutrient level is generally not high enough for this material to be considered fertilizer. Because sand drains freely, beginning gardeners sometimes amend clay soil with sand in an effort to improve drainage. By mixing sand and clay, these gardeners unwittingly make soil cement. What they don’t yet know is that adding organic matter is the key to improving all types of soils. Without organic matter, sandy soil can’t retain water long enough for plant roots to use it. Clay soils, because of their tightly packed particles, are too heavy to convey water. Organic matter is a food source for the macroorganisms and microorganisms, which do the major work of soil building, so it’s an essential component for changing either type of soil. Macroorganisms are primarily made up of earthworms and some insects. Microorganisms are primarily made up of beneficial fungi and bacteria. All the below-ground creatures release plant nutrients as they break down organic matter. In the process, they improve your soil’s drainage and water-holding capacity. The end product of the process of decomposition is the stable, fully decomposed material called humus. As sources of organic material, aged manure, leaf mold, well-decomposed sawdust, peat moss, or any type of compost will give good results. Compost has the advantage that you can make it yourself and be assured of a continuing supply.