Bone meal helps transplants and bulbs put down roots.
Bone meal isn't a rooting tonic. It's phosphorus and calcium, which most garden soils already have enough of, and phosphorus hardly moves in soil anyway. Too much can even stop roots teaming up with the helpful fungi they rely on. Get a soil test before adding any.
What is actually known
Bone meal is mainly phosphorus and calcium, and phosphorus can increase root growth in a roundabout way, through the mycorrhizal fungi that roots partner with, and that is where the belief comes from. But both elements are rarely short in garden and landscape soils, so adding more usually does nothing for rooting. Phosphorus barely moves in soil, about an eighth of an inch a year, and bone meal releases its phosphorus mainly in acidic soil, taking little part in the soil's phosphorus cycle over a short time. Too much phosphorus backfires, because roots stop forming mycorrhizal connections. Get a soil test before adding it.
The evidence
Evidence: checked against 3 sources in the research-based literature.
The 3 sources
Bone meal supplies high levels of phosphorus and calcium, elements that are rarely limiting in non-agricultural soils.
Because phosphorus is very immobile in the soil, it does not move very far in the soil to get to the roots. Diffusion to the root is only about 1/8 of an inch per year, and relatively little phosphorus in soil is within that distance of a root.
Further, CB addition improved soil P availability in the red soil, but not in the fluvo-aquic soil. This could be attributed to that P mainly exists in the form of apatite in bone meal, and H + is necessary to release P from apatite
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Cite this page
Milpa Gardens. "Bone meal helps transplants and bulbs put down roots." Evidence grade: Contested. https://milpa.garden/beliefs/bone-meal-bulb-fertilizer/
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