Bone meal is used when planting new plants.
As a slow release fertilizer, bone meal is primarily used as a source of phosphorous (28 percent by weight). It is often used in planting holes for bulbs to help promote fall root growth. The idea is to mix the bone meal into the soil below where the bulbs will be planted so it can be used by the newly-emerging roots.
Use a handful in the hole before planting trees & shrubs. Add smaller amounts for smaller plants.