There are four main types of soil: clays, silts, sands, and loam. Loam is actually a blend of the first three types, in approximately equal percentages, and usually contains organic matter as well. Typically, the ideal garden soil is usually a sandy, clay loam. Soil acts as a reservoir to hold in moisture and nutrients. A plant's success largely depends on the depth of its soil. Trees need two to four feet of loam topsoil, and shrubs need one to three feet. Vines, groundcovers, annual and perennial flowers, and grasses need at least a foot of quality soil. Before planting flowers, vegetables, and groundcovers, remove all the existing vegetation in the area where you wish to plant. Next, till the area to a depth of eight to ten inches, rake organic material into the soil, and then fumigate to eliminate soil-borne insects, diseases, and weeds. Depending on what you are planting and the soil type in your area, soil preparation may also include altering the p-H level, mulching, changing the grade or slope, and fertilizing. Check with a local nursery for more information on soil preparation and to determine what type of preparation is best for your specific needs.