Fifty plant growing media were prepd. by mixing white peat with digestates from com. biomass gasification plants (and some other org. wastes) and studied for phytotoxicity on Lepidium sativum seeds (germination test). Use of the peat resulted in decreasing pH values of the digestates and a fixation of phytotoxic NH3 on the peat surface according to a cation-exchange mechanism. Six plant growing media (germination rate above 85%, rooting index above 100%) were recommended for practical use in agriculture.