The method of preparation of phosphorus organo-mineral fertilizers with the increase resistance to leaching of mineral components by water based on the impregnation of aspen bark by water solution of КН₂РО₄ and its transformation into low soluble compound Са(Н₂РО₄)₂ was developed. The optimal condition of fertilizers preparation, ensuring minimum leaching of phosphates and potassium were selected. The possibility of enrichment of fertilizers by microelements (Mg, Cu, Zn, Fe) without the loss of their water resistance was shown. The increased resistance of designed fertilizers on the basis of aspen bark to leaching of mineral components by water determines their prolonged action. As a result of vegetation growth experiments the stimulating effect of phosphate organo-mineral fertilizers on the basis of aspen bark was shown.