Bones break down very slowly in a home compost pile and often don't decompose completely before you use the finished compost

You can technically add bones to a compost pile, but they rarely finish breaking down in the timeframe of a typical home composting cycle. Most home compost piles reach finished compost in 6 to 12 months; bones can take 5 to 10 years or longer to decompose fully, depending on their size and the conditions in your pile. This means you'll likely dig them out of your finished compost still intact or only partially broken down.

The main problem is surface area. Bones are dense and hard, and microorganisms work from the outside in. A small chicken bone might break down faster than a beef femur, but even small bones decompose so slowly that most home gardeners find them still present when they harvest their compost. If you do add bones, you're committing to either removing them by hand later or waiting years longer than usual before using that batch of compost.

Key Takeaways

  • Bones decompose in home compost piles but take 5 to 10 years or longer, far beyond the typical 6 to 12 month composting cycle.
  • Small bones like chicken bones break down faster than large ones, but still slowly enough that you'll likely find them in finished compost.
  • Burying bones deep in the center of a hot compost pile speeds decomposition slightly by exposing them to higher temperatures and more microbial activity.
  • Crushing or breaking bones into smaller pieces before composting reduces decomposition time, though they still take years rather than months.
  • Commercial composting facilities with higher temperatures and longer processing times can break down bones completely, but most home piles cannot.

Why bones decompose so slowly

Bones are made mostly of calcium phosphate and collagen, a tough protein. The collagen breaks down over time, but the mineral structure resists microbial attack. Bacteria and fungi need moisture, oxygen, and warmth to work, and they can access only the outer surface of a bone. As the outer layer breaks down, a new hard surface is exposed underneath, so the process repeats slowly, layer by layer.

Temperature matters significantly. In a cold pile or a pile that doesn't heat up much, bones decompose even more slowly. In a hot, actively managed compost pile where temperatures reach 140°F to 160°F, decomposition happens faster, but still not fast enough for most home gardeners to wait. The bone itself doesn't generate heat the way nitrogen-rich materials do, so it just sits there while the rest of your compost breaks down around it.

How to speed up bone decomposition if you add them

If you decide to compost bones anyway, breaking them into smaller pieces before adding them to the pile cuts decomposition time significantly. Use a hammer or saw to crack large bones into pieces roughly the size of your thumb. Smaller pieces expose more surface area to microorganisms, which is the limiting factor in bone breakdown.

Bury the bone pieces deep in the center of your pile rather than mixing them throughout. The hottest part of an active compost pile is the center, where temperatures climb highest. Placing bones there exposes them to more heat and more microbial activity than they'd experience on the edges or near the surface. Turn your pile regularly to keep it hot and to move bones toward the center as the pile settles.

You can also soak bones in water for a few days before adding them. This softens the outer layer slightly and may speed up the initial breakdown, though the effect is modest. Some gardeners boil bones first to remove meat and fat, which can attract pests; boiling also softens the bone slightly, though again, the impact on total decomposition time is small.

What to do with bones instead of composting them

If you have a lot of bones or don't want to wait years, several other routes work better. Many municipal composting programs accept bones because their facilities reach much higher temperatures (often 140°F to 160°F or hotter) and process material for longer than home piles. Check whether your city or county runs a composting program and what they accept; bones are often on the list.

You can also bury bones directly in your garden bed, away from where you'll plant in the next year or two. They'll break down in the soil over time and add minerals like calcium and phosphorus. Bury them at least 12 inches deep to keep them away from pets and wildlife. This works well if you have space and don't mind waiting.

Bone broth is another option if you have bones from meat you've cooked. Simmer them for 12 to 24 hours to extract collagen and minerals into the broth, then compost what's left. The remaining bone material is softer and breaks down faster than raw bones. You also get a useful product out of it.

Bones and pest problems

Raw bones, especially those with meat still attached, can attract rats, raccoons, and other animals to your compost pile. This is often a bigger practical problem than slow decomposition. If you do add bones, remove any meat or fat first, bury them deep in the center of the pile, and make sure your bin has a find lid and base that animals can't chew through.

Cooked bones are less attractive to pests than raw ones, but they're still not ideal for open compost piles in areas with wildlife. If you have a fully enclosed bin with a locking lid, cooked bones are much safer to add. If your pile is open or loosely covered, skip bones altogether and use one of the alternatives listed above.

Bones in finished compost

If you've already added bones to your compost and it's now ready to use, you have two choices: screen them out or leave them in. A straightforward wire mesh screen or hardware cloth stretched over a wheelbarrow lets you sift finished compost and catch bone fragments as they fall through. This takes time but works well if you have only a few bones.

Alternatively, you can spread the finished compost in your garden and pick out any visible bone pieces by hand as you work. This is tedious but necessary only if the bones are large enough to interfere with planting or if you're concerned about them in a vegetable bed. Small bone fragments left in compost won't harm plants and will continue breaking down slowly in the soil.

Frequently Asked Questions

Can I compost cooked chicken bones?

Yes, cooked chicken bones break down faster than raw ones because cooking softens them, but they still take several years to decompose fully in a home pile. Bury them deep in the center of a hot pile and break them into small pieces first. They're less likely to attract pests than raw bones, but still pose some risk if your pile isn't fully enclosed.

Will bones hurt my plants if I leave them in finished compost?

Small bone fragments won't harm plants. Bones add calcium and phosphorus as they break down, which are actually beneficial. Large bone pieces can interfere with planting or digging, so screen them out if they're visible. Leaving them in the soil to decompose further is fine if you don't mind them being there.

How long does it take for a bone to fully decompose?

Small bones like chicken bones take 5 to 10 years in a home compost pile; large bones like beef femurs can take 10 to 20 years or longer. Commercial composting facilities with higher heat and longer processing times can break down bones in 6 to 12 months. The exact timeline depends on bone size, pile temperature, and moisture.

Should I crush bones before composting them?

Yes, crushing bones into small pieces significantly speeds decomposition by increasing surface area. Use a hammer or saw to break them into thumb-sized pieces or smaller before adding them to your pile. This won't make them decompose in months instead of years, but it will cut the timeline noticeably.

Can I put bones in a worm bin?

Bones are not recommended for worm bins. They decompose too slowly for the worm bin environment and can disrupt the balance of the system. Stick to softer materials like food scraps, leaves, and paper in a worm bin, and compost bones in a traditional pile or send them to a municipal composting program instead.