Soilborne pathogens can devastate crops, causing economic losses for farmers due to reduced yields and expensive management practices. Fumigants and fungicides have harmful impacts on the surrounding environment and can be toxic to humans. Therefore, alternative methods of disease management are important. The disease suppressive abilities of composts have been recognized for several decades, and significant research has been done in order to identify substrates with effective suppression. The mechanisms of suppression are mainly biological, but abiotic aspects of the composts, such as pH, carbon to nitrogen ratio, and maturity, interact with pathogenic and biological control processes and determine efficacy of suppression. For example, Fusarium wilt is aggravated by high ammonium-N composts (Cotxarrera et al., 2002), and mature composts with low levels of labile compounds more effectively suppress Rhizoctonia damping-off (Trillas et al., 2006). Identification of these abiotic factors can increase efficacy of disease suppression of composts. In addition, inoculating composts with biological control agents, such as Trichoderma, has been found to increase suppressive ability in many cases.