Bones can be composted, but they decompose so slowly that most home composters should avoid them
Bones break down in a compost pile, but the process takes years rather than months. A standard backyard compost system — whether hot or cold — will not fully decompose bones before you finish composting other materials and want to use the finished product. Bones are dense, made mostly of calcium and minerals, and lack the nitrogen that microorganisms need to work quickly. If you do add bones, they will still be recognizable chunks when your compost is ready.
The real question is whether the time and space cost is worth it. Most home gardeners find that leaving bones out of the pile and composting everything else produces usable compost faster. If you have bones to dispose of, burying them directly in garden beds or a separate pit works better than mixing them into an active compost system.
Key Takeaways
- Bones decompose in compost but take three to five years or longer, while your finished compost may be ready in six to twelve months.
- Bones attract rodents and other animals to your pile, which is a bigger practical problem than slow decomposition.
- Burying bones directly in a garden bed or a separate hole in the ground breaks them down faster than composting them in a pile.
- Crushed or ground bones (bone meal) are already processed and can be mixed into compost or soil without the decomposition wait.
- Cooked bones with meat, fat, or seasoning should never go in a home compost pile because they attract pests and create odor problems.
Why bones decompose so slowly in compost
Bones are made of collagen (a protein) and mineral compounds like calcium phosphate. Microorganisms in compost can break down the collagen, but they work slowly because bones have a very high carbon-to-nitrogen ratio and are physically dense. The microbes that drive hot composting need nitrogen-rich materials like food scraps or grass clippings to multiply quickly. Bones provide carbon but almost no nitrogen, so the pile does not heat up around them the way it does around other materials.
In a cold compost pile, decomposition is even slower. Bones can sit in cold compost for five years or more without fully breaking down. Even in an actively managed hot pile where you turn the compost regularly and maintain the right moisture, bones will still be present as hard fragments when the rest of the pile has become dark, crumbly finished compost.
The pest problem is worse than slow decomposition
Raw bones in a compost pile attract rats, raccoons, opossums, and sometimes bears, depending on where you live. These animals dig into the pile looking for bones and other food scraps, which breaks apart your composting work and spreads material across your yard. Once animals know your pile contains food, they return repeatedly.
Even if you bury bones deep in the center of the pile, animals can smell them. A compost bin with a find lid and no gaps helps, but most home compost systems are not designed to keep out determined animals. If you live in an area with wildlife, adding bones to your pile is more likely to create a pest problem than to produce usable compost.
Cooked bones should never be composted at home
Bones with meat still attached, bones with fat, or bones that have been seasoned or boiled should not go into a home compost pile. These attract pests even more aggressively than raw bones, and they create strong odors as they decompose. The fat and meat also introduce pathogens and can throw off the balance of your pile.
Cooked bones from a roasted chicken, beef stew, or soup are better disposed of in the trash or buried in a separate pit away from your main compost system. If you want to compost them at all, bury them at least two feet deep in a garden bed where animals cannot easily dig them up.
Burying bones directly in the garden works better
If you want bones to break down in your yard, dig a hole at least twelve inches deep in a garden bed or unused corner and bury them there. Soil organisms, moisture, and time will break them down faster than a compost pile because the bones are in contact with living soil and are not competing with other materials for microbial attention. Bones buried in soil typically break down in two to three years, which is still slow but faster than in a compost pile.
This method also keeps bones away from your compost system and away from animals that might dig in your pile. Mark the spot so you do not accidentally dig there later, and wait at least a year before planting directly over the burial site.
Bone meal is the practical alternative
If you want the nutrients from bones without the decomposition wait, buy bone meal or make it yourself by baking bones in an oven at 350°F for about an hour, then grinding them in a food processor or with a hammer. Bone meal is already broken down into a form that plants can use, and it releases phosphorus and calcium into your soil over time.
You can mix bone meal directly into compost, sprinkle it on garden beds, or work it into soil before planting. It costs less than waiting years for whole bones to decompose, and it does not attract animals or create odor problems. If you have a lot of bones, this is the most practical route.
What to do with bones from meat and fish
Bones from cooking — chicken bones, fish bones, beef bones — have different handling needs depending on whether they still have meat or fat on them. Raw bones with no meat are safer to compost than cooked bones, but they still attract animals and decompose slowly. If you have a find, animal-proof compost bin and are willing to wait years, raw bones can go in. Otherwise, bury them or turn them into bone meal.
Fish bones are smaller and break down faster than large animal bones, but they also smell stronger and attract more pests. Bury fish bones deep in the garden or in a separate compost system away from your main pile. Never add fish bones to a compost pile that is close to your house or near areas where children or pets play.
Frequently Asked Questions
How long does it actually take bones to fully decompose in compost?
In a hot, actively managed compost pile, bones can take three to five years. In a cold pile, they may take seven years or longer. Most home gardeners finish composting other materials in six to twelve months, so bones will still be hard fragments in your finished compost.
Can I compost bones if I have a sealed compost bin?
A sealed bin with a tight-fitting lid reduces the pest problem, but bones still decompose very slowly inside it. The bin also takes up space that could be used for materials that break down faster. If you have a sealed bin and want to use it for bones, bury them at the bottom and do not expect finished compost for several years.
Are eggshells and bones the same thing when composting?
No. Eggshells are much thinner and break down in a few months, especially if you crush them first. Bones are dense and mineral-heavy, so they decompose much more slowly. Eggshells are fine to add to any compost pile; bones are not.
What if I crush the bones into small pieces before composting?
Crushing bones speeds up decomposition somewhat because it increases surface area for microbes to work on, but it does not solve the core problem. Crushed bones still take years to fully break down, still attract animals, and still do not provide nitrogen to heat the pile. Grinding bones into powder (bone meal) is more effective, but at that point you might as well buy bone meal.
Can I compost bones in a worm bin?
No. Bones are too hard and dense for worms to process, and they will sit in the bin unchanged. Worms work best with soft materials like food scraps, leaves, and grass. Bones belong in a separate system or buried in the garden.