Bones break down very slowly in compost and can attract pests, so most home composters should avoid them

You can technically put bones in compost, but they will sit there for years without fully decomposing. A chicken bone might take 6 to 12 months to soften noticeably; larger beef bones can take several years. During that time, they create two real problems: they draw rats and other animals to your pile, and they can still be hard enough to damage a blender or food processor if you use finished compost in a garden bed and later harvest root vegetables.

The exception is a hot compost system — one that reaches and holds 140°F or higher for weeks at a time. At that temperature, bones soften faster and pests are less likely to dig. But most home piles never get that hot, especially in cool climates or during winter. If you are not actively managing temperature with frequent turning and the right carbon-to-nitrogen ratio, bones are more trouble than they are worth.

Key Takeaways

  • Bones decompose so slowly in home compost that they often outlast the pile itself, making them impractical for most backyard systems.
  • Bones attract rats, raccoons, and other animals to your compost, which can create a pest problem in your yard or neighbourhood.
  • Only bones in a hot compost system (held above 140°F) break down in a reasonable timeframe; cool piles should exclude them entirely.
  • Burying bones directly in garden beds or in a separate bone-only pit is faster and keeps pests away from your main compost.

Why bones are slow to decompose

Bones are made mostly of calcium phosphate and collagen, a protein wrapped around a mineral core. Microbes can eat the collagen, but it takes a long time — and they work much faster in warm, wet conditions than in a cool pile. The mineral part (the hard white or cream-coloured material) does not decompose at all; it just gets smaller as the collagen around it breaks down.

In a hot compost pile that reaches 140°F and stays there for several weeks, the collagen softens and breaks down faster. But in a cool pile — which is what most home gardeners have — the process stalls. A chicken bone might soften enough to crumble by hand after a year, but a beef knuckle or rib can take three to five years, and some gardeners report bones still visible in finished compost after a decade.

The pest problem bones create

Bones smell like food to rats, raccoons, opossums, and other animals. They will dig into your pile to reach them, which can scatter compost across your yard and create a mess. Once an animal finds bones in your compost, it may return repeatedly, even after the bones are gone. This is especially true in urban and suburban areas where wildlife populations are dense.

If you live in a neighbourhood where rodents or raccoons are already a problem, bones in an open compost pile are almost may provide to make it worse. Even a closed bin with a latch can be breached by a determined raccoon. The safest approach is to keep bones out of compost altogether if you want to avoid attracting pests.

When bones might work: hot composting

A hot compost system is one where you layer nitrogen-rich materials (grass clippings, food scraps, manure) with carbon-rich materials (dry leaves, straw, shredded paper) in a ratio that generates heat as microbes break everything down. When done correctly, the pile reaches 130°F to 160°F and stays there for weeks. At that temperature, bones soften much faster — sometimes in 3 to 6 months — and the heat also kills pathogens and weed seeds.

To maintain a hot pile, you need to turn it every week or two, monitor moisture (it should feel like a wrung-out sponge), and add materials in the right proportions. Most home gardeners do not do this consistently, so their piles stay cool. If you are already managing a hot pile and want to add bones, chop them into small pieces first — this increases surface area and speeds decomposition. Even then, expect them to take longer than softer materials.

Better alternatives to composting bones

Burying bones directly in a garden bed is faster and keeps them away from pests. Dig a hole at least 12 inches deep, place the bones in the bottom, and cover with soil. The bones will soften and break down in place over time, and the nutrients will leach into the surrounding soil. This works especially well for perennial beds where you are not digging frequently.

Another option is to create a separate bone-only pit away from your main compost pile — perhaps in a corner of the garden or under a shrub. Bury bones there as you accumulate them, and let them decompose out of sight. After a year or two, the area becomes a nutrient-rich spot for planting.

If you have a lot of bones, you can also save them for a bone broth project. Boiling bones extracts minerals and collagen into a liquid you can use in cooking or pour directly onto garden beds. This uses the bones' nutrients when ready rather than waiting years for them to decompose.

What to do with cooked versus raw bones

Cooked bones are more brittle and break apart faster than raw bones, so they decompose slightly quicker in compost. However, they still take months to years, and they still attract pests just as readily. The cooking process does not change the fundamental problem: they are hard, slow to break down, and smell like food to animals.

Raw bones are denser and take even longer. If you are choosing between the two for your compost pile, cooked bones are marginally better — but the difference is not large enough to make bones a practical compost ingredient in a cool pile. Either way, burying them or keeping them out of compost entirely is the simpler choice.

Signs bones are becoming a problem in your pile

If you have already added bones to your compost and notice animal activity — digging, scattered compost, paw prints, or droppings — remove the bones when ready. Dig them out, bury them separately in the garden, or throw them away. The sooner you stop attracting animals, the sooner they will stop visiting.

If your pile smells strongly of decay or ammonia, or if you see maggots, bones are not the cause — that is usually a sign of too much nitrogen or too much moisture. But bones can make an existing pest or smell problem worse, so removing them is still a good step.

Frequently Asked Questions

Can I compost fish bones?

Fish bones are smaller and softer than mammal bones, so they break down faster — usually in 3 to 6 months in a cool pile. However, they smell very strong and attract pests just as readily as larger bones. If you compost fish scraps, bury them deep in the pile or in a separate pit to keep the smell contained.

What about eggshells — are they the same problem as bones?

No. Eggshells are safe to compost and break down in 2 to 3 months. They are made of calcium carbonate, which dissolves much faster than bone mineral. Crush them first to speed the process, and they will not attract pests the way bones do.

Can I put bones in a Bokashi bucket?

Bokashi systems ferment food scraps using special microbes, and they can handle bones better than traditional compost. However, bones still do not fully break down in the Bokashi process — they ferment but remain hard. You would still need to bury the fermented bones in soil or compost afterward, so it is an extra step with no real advantage.

Will bones hurt my finished compost if I use it in a vegetable garden?

Hard bone fragments can damage garden tools or a tiller, and they can chip teeth on a food processor if you harvest root vegetables and process them. Smaller, softened pieces are not a safety issue, but you may still find visible bone fragments in finished compost years later, which is unsightly.

Is it safe to bury bones directly in a vegetable bed?

Yes. Bury them at least 12 inches deep so they do not interfere with planting or digging. They will not introduce pathogens or toxins — they are just slow to break down. This method is actually safer than composting them because the bones stay in one place and do not attract animals to your pile.