Plants require many nutrients and minerals to survive, which are supplied either from the soil or via fertilizer. One of these minerals, phosphorus, aids plants with bud set and fruiting. Commercial fertilizers usually supply phosphorus to soil and plants, though there are many organic and inorganic sources of the mineral.
The most common source of phosphorus in commercial fertilizer blends, rock phosphate is quarried then ground into grit prior to use. Rock phosphate contains up to 35 percent pure phosphate and provides the base source for all phosphate. Sulfur treatments prior to packaging improve the solubility of rock phosphate so that plants can absorb more of the mineral from the soil.
Animal bones contain approximately 10 percent phosphorus, making them a suitable source for the fertilizer. Bones are crushed and ground into a fine grit then added to the soil alone or added to other fertilizers. Bones are often steamed before crushing, as this releases more phosphorus from the material and may increase the amount to 13 percent. Bone meal is considered suitable as an organic fertilizer compound.
Manure provides not just phosphorus but nitrogen as well. Usually only manure from herbivores is used in gardens, as other manures tend to burn plants. Composting the manure first prevents most issues with plant burning and ensures all the nutrients are broken down and easily accessible by the plants. The amount of phosphorus in manure is variable, depending on the animal it came from, the diet of the animal and whether the manure is composted or not.