The present invention aims at providing a method for producing a nutrient solution for plant culture utilizing an organic material and providing a method of hydroponic culture in which a plant can be cultured while directly adding the organic material to the nutrient solution. The present invention provides a method for producing a biomineral-containing substance comprising establishing a microbial ecosystem necessary for stable mineralization of organic material by adding the organic material to water gradually or at one time and fermenting the resulting mixture and a method of hydroponic culture comprising utilizing the biomineral-containing substance obtained according to the method as at least a part of the nutrient solution and culturing the plant while directly adding the organic material to the nutrient solution.
