Bone meal is almost exactly what it sounds like: ground up bones. I say almost, because bone meal also contains cleaned slaughterhouse waste products, much the way blood meal is processed.
Bone meal is an organic fertilizer, high in phosphorus (as much as 15%). Bone meal also contains 3% nitrogen. Those minerals are released into the soil at a rate that is dependent on how finely everything was ground up and on soil acidity. Coarse grindings take longer to break down than material that is ground more finely. According to a study conducted by Colorado State University, bone meal labeling can be a bit confusing. They also found that phosphorus from bone meal is only available to plants if the soil pH is below 7.0, something very unlikely in the Bay Area without acidification. At the same time, lavender plants devour phosphorus and may need supplementing.
Before feeding plants or amending soil with bone meal, it is very important to have your soil tested by a reputable local lab. Most Bay area soil is very high in phosphorus, but not always. Unfortunately, over-the-counter soil tests are too unreliable to be worthwhile. Also, amending your soil with bone meal may attract raccoons or dogs, who will dig up your plants in search of a hidden treat that they will never find.
Invest in a good soil test to see if your garden can benefit from bone meal.
You can grow a surprising amount of food in your own yard. Ask me how!