The invention relates to a method for preparing a suspension containing phosphate stepwise directly from raw materials, from phosphoric acid of fertilizer quality, a base and organic additives. In accordance with the method, the phosphoric acid is preneutralised with the base, the organic additives are added, nucleation is controlled and phosphate salts are cooling crystallised in order to form a suspension. The phosphate suspension prepared with the method of the invention is applicable to seed coating.