Using Compost as a Mulch
Compost can also be used as organic mulch on the surface of the soil in place of peat moss, pine straw, etc. Organic mulches are valuable because they reduce rainfall runoff, decrease water evaporation, keep the soil friable and easier to cultivate and help control weeds. Recommended thicknesses of mulch layers are 2 to 3 inches for deciduous shrubs and trees, vegetable, and rose beds; 3 inches for flower beds; and 4 inches for shallow-rooted, acid-loving plants.
Compost as a Planting Medium
Compost may be used in potting soil; however, no more than 25-30 percent of the potting soil should be compost. Frequently, compost will continue to decompose and there can be a significant volume reduction of the potting soil. Also, most weed seeds are killed by the high temperatures of the composting process, but not all. Some weed seeds are heat resistant and will not be killed. Used properly; however, minimal problems will occur with weeds in the use of compost.