The present invention relates to a method for producing coco peat plant growth substrate. More specifically the present method relates to a method for producing coco peat plant growth substrate, which method comprises acidifying a coco peat by adding to the coco peat an aqueous solution comprising: nitric acid, phosphoric acid and sulfuric acid, wherein 1 to 100 mol H + is added per cubic meter coco peat, thereby providing coco peat plant growth substrate with a pH of less than 5.