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As more horticultural producers in the United States transition to organic production practices, they are challenged in finding consistent and economically viable sources of suitable potting media. Commercial, peat-based media approved for certified organic production are available and custom peat-based mixes that use certified organic fertilizers could also be used. Both of these options, however, are usually expensive and their sustainability is questionable given the dependence on peat, a resource generally considered to be nonrenewable, and processed organic fertilizers shipped long distances. One potential solution to this problem is the use of locally composted organic wastes that can serve as a partial or complete potting medium and nutrient source. Considerable research has been performed over the past two decades evaluating composts, derived from various feedstocks, as potting media constituents in vegetable and ornamental plant production (Burger et al. 1997; Fitzpatrick 2001; Ozores-Hampton and Vavrina 1999; Raviv et al. 1998; Sánchez-Monedero et al. 2004; Sterrett 2001; Wilson et al. 2001a 2001b). This research generally has shown that composts can be used successfully as partial, and sometimes as complete, substitutes for peat. However, in many of these studies, the nutrient contributions are not addressed because the composts are considered only as substrate alternatives to peat. The plant-available nutrient contribution, a characteristic of high importance to organic producers, is often presumed to be inadequate. In addition to nutrient content and availability, particularly for nitrogen, other important characteristics of composts used as potting media include maturity and/or stability, salinity, pH, particle size, and water-holding capacity. Compost maturity refers to the suitability of the material for a particular use while stability is the resistance of the material to further microbial decomposition (Sullivan and Miller 2001). A mature compost is one that does not undergo further active microbial decomposition (heat up) and is free of phytotoxic substances. In addition to these considerations, certified organic producers have limited choices of organic waste feedstocks for compost production. Composts made from biosolids (sewage sludge), for example, are not permitted in certified organic production systems (USDA 2005). In 1999, the greenhouse operation of Berea College Farms, located in eastern Kentucky, began a transition from conventional to certified organic production. Local sources of organic waste and compost were considered for potting media and nutrients. The College initiated a food residuals composting program and began Compost Science & Utilization, (2005), Vol. 13, No. 2, 150-156