How to Make Garden Fertilizer Out of Bones

Bones are an excellent source of minerals and nutrients for your garden’s soil, and bone meal is commonly used as an ingredient in organic fertilizer mixes as well as a food additive for livestock. If you’ve seen “NPK” written on bags of fertilizer at the garden store or three numbers in a row like 5-4-5, those are to identify the levels of the three most essential elements for plant health—nitrogen, phosphorus, and potassium. Bone meal is particularly high in phosphorus and also supplies some nitrogen and calcium. Phosphorus is an essential nutrient for the development of roots and flowers, while calcium is vital for plant structure and fruit development.

Making bone meal is very simple. Typically, bone meal that you can buy at agricultural supply stores is made from cattle bones as a byproduct of the beef industry. They are steamed and ground into a powder. Making bone meal at home is the same process.

First, boil your bones to dissolve all of the meat and gristle still clinging to them. If this sounds like making bone broth—you’re right! We always use our bones to make broth or stock first. Just avoid using salt or add it after the bones have been removed to ensure no salt makes it into your bone meal and, therefore, your garden soil.

After the bones are clean of any meat and fat, bake them in the oven until they become dry and brittle. Thick bones from animals like deer and elk will be very dense and take a lot of cooking before they can be broken down easily. While hollow, thin bones like those from chicken and gamebirds may be soft enough to break apart right after making stock. For deer bones, we typically put them in the pressure cooker for a while first to speed up the process.

Once the bones are dry and fragile, it’s time to pulverize them. For smaller bones, you can put them in a cloth sack or towel and roll over them with a heavy rolling pin or hit them with a mallet until they break apart. Larger bones will likely take something a little more heavy-duty.

For deer bones, we take them outside and use a tamper or digging stick. When the pieces are less than an inch in diameter, you can transfer them to a high-power blender or mortar and pestle to break them down even further into a fine powder, which will help it break down faster in the soil, but isn’t completely necessary.

Now that you’ve made your bone meal, it should last for at least a year stored in a cool dry place. Using it is as simple as sprinkling it over the surface of your garden soil and gently working it in. It’s a slow-release fertilizer and won’t burn your plants if you add too much like some fertilizers can, but you should still be judicious in using the right amount for your space. Adding too much phosphorus will just cause the excess to run off into waterways, creating pollution. Conducting a soil test is the best way to know if your soil really needs a boost of phosphorus or calcium, but if you’ve noticed weak or stunted roots, a lack of flowers on your plants, or unusually dark or purplish older leaves on your plant, that may be a sign it would benefit from bone meal. A general rule of thumb is to add no more than 10 pounds per 100 square feet, or a teaspoon per plant start for larger plants and bulbs.

One downside of bone meal is that it can attract animals like dogs and raccoons to your garden since it often smells like a delicious treat to them. Because we have a dog that likes to dig where she shouldn't, we avoid this by applying it in late fall or early spring and working it into the soil, so the scent is covered. Adding mulch, like straw or composted leaves, on top can help with this as well.

Because it is a slow-release fertilizer, this has the added benefit of giving the bone meal time to break down in the soil and make the nutrients more available by the time you’ve planted your garden. You can also put a small amount of it at the bottom of the transplanting hole before you plant your seedlings, which will generally disguise the smell from any interested critters.