Bone meal fertilizer is used to increase phosphorus in the garden. Most of them has a NPK of 3-15-0. Phosphorus is essential for plants in order for them to flower. Its phosphorus is easy for plants to take up. Using bone meal will help your flowering plants, like roses or bulbs, grow bigger and more plentiful flowers.
It is also useful for balancing out other high nitrogen, organic soil amendments. For example, rotted manure is an excellent source of nitrogen but it tends to lack significant amounts of phosphorus. By mixing bone meal fertilizer in with rotted manure, you have a well balanced organic fertilizer.