Bone meal is a wonderful natural fertilizer that has been used by farmers and gardeners for centuries to improve root growth and flowering in plants. It is the premier source of phosphorus for use in organic gardening and is made from ground-up bones (either cooked or steamed). It can be applied to the overall garden at the time of initial soil prep in the spring, or can be sprinkled in the hole when transplanting starts or perennials to encourage the development of new roots.
Along with Nitrogen (N) and Potassium (K), Phosphorus (P) is one of the three major nutrients, or "macronutrients" needed by all plants. Plants use it for:
There is an impending challenge with phosphorus: it is in finite supply, We don't recycle bones anymore (bone meal is becoming more expensive), and the places where rock phosphate is mined are running out. We are approaching "peak phosphorus".
Our food system is dependent on replacing the phosphorus that is removed from the soil, and unless we start recycling bones into bone meal, we're going to run out of phosphorus in 50-70 years. There is more information on this page at MIT. This is another reason to learn to garden for nutrition, now. You can read more about how to garden for nutrition on the organic fertilizer page.
Bone meal is not taken up directly by plants, but is first digested by soil microorganisms, which act as intermediaries between the soil and the plant, delivering to them just the amount of phosphorus they need.
This is one reason why compost is so very important - it's not just supplying nutrients - it supplies the billions of microorganisms that plants need to make the nutrients available. It’s a symbiosis thing.
This is also why it is more challenging to grow an organic garden in pots or raised beds that are filled with store-bought potting mix. Most potting mix has very few beneficial soil microorganisms in it, which are the plants’ friends and allies.
Most plants do not need a lot of phosphorus, but the little bit they do need is critical.
Phosphorus deficiency can produce the following symptoms:
Some other mineral deficiencies, as well as pH or water issues, may cause similar symptoms, so the best way to determine if your soil needs phosphorus specifically is to do a soil test. I recommend contacting your local State University Extension Service for this. It usually only costs about $20. and will let you know what, if anything, is out of balance in your soil. It'll save you money in the long run by preventing unnecessary fertilization.
Bone meal is a slower-releasing form of phosphorus fertilizer than “superphosphate” or “triple phosphate", the most popular non-organic forms. It is more stable in the soil, and will not wash away like chemical fertilizers will (which then pollute the groundwater). It will also not “burn” plants, which occurs when chemical fertilizers are too high in concentration and become caustic to the plant tissues, killing them.
It is believed by some that bone meal can carry BSE, or “bovine spongiform encephalopathy” - so-called “mad cow disease”. The human version of this disease is called Creutzfeldt-Jakob disease, and three cases of it in Britain developed in people who were rose gardeners and who regularly applied bone meal to their roses.
However, in doing deeper research on this, I found two important things: 1) there is no mad cow disease in the US, and 2) the meal in the US is processed in a different way than in Britain. In the US it is processed using both very high temperatures and a chemical solvent, whereas in Britain, they mostly only use heat (or at least they used to). The chemical solvent used in the US kills BSE.
So the take-away is:
1) use US-manufactured bone meal, and
2) wear a mask when you work with dust of any kind.