4-10-0. As an organic slow-release fertiliser, bone meal is primarily used as a source of phosphorus and protein. Phosphorus promotes early growth, root formation and fruit development in trees, shrubs and other garden plants. Bone meal is best suited for slightly acidic soils (below pH 7) for the bone meal to be most available to the plants. 1.5kg bag. Application rates depend on your soil type, but the general rate is 10lb per 100 square feet.