Compost comprises symbiotic cultured mixt. of Thermoactinomyces SK053 sp. nov (FERM P-13598) having wide pH range of 5.3-10.8, lignin solubilising and fibrinolytic properties and Clostridium thermocellum biovar. SK522 (FERM BP-3459) having growth temp. range of 40-80, pref. 65-72 deg.C and active fibrinolytic property, partic. in the presence of the other fibrinolytic microorganism, Thermus aquaticus biovar SK542 (FERM BP-3382) having growth temp. range of 40-82, pref. 72-76, more pref. 75-85 deg.C, pH range of 4.0-11.3 and proteolytic enzyme and carotinoid yellow pigment productivities.    Thermophilic actinomycetes Thermoactinomyces SK053 (FERM P-13598), Clostridium thermocellum biovar SK522 sp. nov. (FERM BP-3459) and Thermus aquaticus biovar SK542 (FERM BP-3382) including aerobic fibrinolytic microorganisms having optimal temp. of 22-35 deg.C (e.g. Bacillus fimi and Actinomyces melanocyclus), anaerobic fibrinolytic microorganisms having optimal temp. of 25-37 deg.C (e.g. Clostridium werneri and Plectridium cellulolyticum) and thermophilic fibrinolytic microorganisms having optimal temp. of 55-65 deg.C (e.g. Clostridium thermocellum and Bacillus cellulosae dissolvens) and denitrifying fibrinolytic microorganisms having optimal temp. of 35 deg.C (e.g. Bacterium cellaresolvens) are used for fermentation of kitchen waste contg. fibrous materials, partic. difficultly degradable fibrous material and conventional medium and used together with conventional additives and carriers to give culture medium for pots.    ADVANTAGE -   Culture medium has improved water content control, aeration and regeneration of aggregation of soil without fear of injury by continuous cropping.    In an example, a mixt. of raw materials composed of 100 l each of peat, vermiculite, pumice particles and husk, 40 l of rice bran and 20 l of the mixt. of seed culture of SK053, SK522 and SK053 was fermented and used for culture of cucumber. Crops with satisfactory quality were 1769.6g, while conventional culture gave corresp. crops of 1091.8g.