A method for stimulating plant disease-suppressive activity, such as soil- and seed-borne fungal diseases- and saprophytic moulds-suppressive activity, in Sphagnum moss biomass is provided. In said method freshly harvested and/or air-dried Sphagnum biomass is heat treated, thereupon a flow of air heated to a temperature within a range of 50-80 °C is conveyed thereto during a predetermined period of time. Sphagnum biomass is preferably selected from naturally occurring Sphagnum species, in particular, Sphagnumfuscum. A plant disease-suppressive growing medium and uses thereof are further provided.
