The invention relates to a growth stimulator for the cultivation of mushrooms, which is freely available and based on microbes, so as to achieve optimum utilisation of substrate and inoculation material. A search for raw materials amongst the unsterile biomasses which are still available has revealed that activated sludges from effluents, preferably from the processing of liquid manure from industrial animal production units, which are of particularly varying nature and variable composition, depending on the substrates and environments, are especially suitable for the production of growth stimulators for the cultivation of mushrooms. To avoid the risk of the development of microbes which compete with the mushrooms, the activated sludge is sterilised by heating for 0.5 to 2 minutes under a super atmospheric pressure to 105 DEG C to 200 DEG C, preferably at a pH of 8 to 11, which gives a dry product with stable biochemical activity and good metering properties. After an addition of preferably 25 to 50 g of chemically-thermally treated activated sludge from liquid manure processing, particularly advantageously at the same point in time as the inoculation, the mushroom yield exceeded the yield on unsupplemented substrate by almost 50%. The simplified procedure used is outstandingly suitable for the large-scale cultivation of mushrooms.
