Does bonemeal promote bigger and stronger plants through root growth?

Question

There are many web sites on how to use bone meal with claims like "Using bone meal will help your flowering plants, like roses or bulbs, grow bigger and more plentiful flowers." Is this true for all plants, just vegetables and bulbs or not at all?

Answer 1

It is going to be true if it contains nutrient(s) that are in short supply.

Bonemeal is considered a slow-release high phosphate fertilizer: bones are primarily apatite - a Calcium Carbonate Phosphate, and the phosphate is more tightly bound than in mined phosphates which are often just simple salts (ie. that dissolve easily). It also has a small quantity of nitrates, and I would expect it to make a good source of Calcium (a micronutrient).

So if your soil is short of phosphate relative to your plant's requirements, then yes it would be a good amendment. If the soil isn't short, then you're not going to see much change. Too much and you may even see damage (eg. fertilizer burn). This is true of any required resource of nutrient. E.g. Extra water is only going to be beneficial if it is dry.

Answer 2

The answer, according to my old Horticultural College lecturer, is no, it's not going to do much for your plants at all, because it takes so long to break down.

UPDATE JUNE 2014: Here's confirmation of the science behind what I've said - I note I've been marked down two points, one of which was done yesterday (no prizes for guessing who that one might be from):-

http://puyallup.wsu.edu/~Linda%20Chalker-Scott/Horticultural%20Myths_files/Myths/Bonemeal.pdf

The only other thing I can find which Linda Chalker doesn't mention is that the phosphorus content in bonemeal is only available to plants growing in soil with a ph of 7 or less, so if your soil is alkaline, the plants won't be able to access it anyway. This was the result of a study carried out by Colorado State University into organic fertilisers - there's a link to it under Wiki.