What Cannot Go in Compost? Common Mistakes to Avoid

Getting started with composting is exciting — but it's easy to make mistakes early on that lead to smelly piles, pest problems, or compost that's not safe to use in the garden. Understanding what doesn't belong in your bin is just as important as knowing what does.

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Items to keep out of your home compost bin

Meat, fish, and seafood

Raw or cooked meat and fish are rich in proteins and fats that break down to produce strong odours, and they attract pests like rats, flies, and cockroaches — especially in outdoor open bins. They're also slow to break down and can create anaerobic pockets in the pile.

If you produce a lot of meat and fish waste, a Bokashi system is designed specifically for this. Bokashi uses a fermentation process rather than aerobic composting, making it safe and effective for meat and dairy.

Dairy products

Dairy — milk, cheese, yoghurt, butter — has the same problems as meat: strong odour when decomposing, pest attraction, and slow breakdown. Use a Bokashi system for dairy. Small amounts of egg-based food scraps are generally fine.

Pet waste (dogs and cats)

Dog and cat faeces contain pathogens including bacteria, viruses, and parasites that can survive composting temperatures in standard home systems and contaminate the finished compost. Never add pet waste to a compost bin that will be used on edible plants.

There are specialist pet waste digesters available if you want to deal with this waste sustainably — these are separate from your main compost system.

Diseased plants

Plants showing signs of disease (powdery mildew, root rot, fungal infections) should not go in the compost. Standard home compost piles don't reliably reach the temperatures needed to kill pathogens, and you risk spreading disease to your garden when you apply the finished compost.

Weeds that have set seed

Mature weeds with seed heads can survive in compost that doesn't reach 55–60°C. If you add seeding weeds to a cold compost pile, you may end up spreading them throughout your garden when you apply the compost. Either hot compost (which kills seeds reliably), or dispose of seeding weeds through your council green waste bin.

Glossy paper and coated cardboard

Glossy magazine pages and coated cardboard (like shiny cereal boxes or waxed produce boxes) contain coatings that inhibit microbial breakdown. They take far longer to decompose and can leave residue in the finished compost. Use uncoated paper and cardboard only.

Plastics, metals, and glass

These don't break down in a compost pile and will contaminate your finished compost. Even small pieces of plastic can end up in your garden soil. Be particularly vigilant about:

• Plastic-coated twist ties on bread bags (remove before composting the bag elsewhere)
• Staples in paper and cardboard (minor, but worth removing where possible)
• Plastic windows in envelopes (remove before composting the envelope)
• Plastic tea bag seams (check your brand before composting)

Plants treated with persistent herbicides

Clopyralid and aminopyralid are herbicides sometimes used on lawn grass and broadleaf plants. They can persist through composting, manure, and into finished compost — where they can then damage sensitive plants in your garden. If you've recently used broadleaf herbicide on your lawn, don't add those clippings to the compost for several weeks.

Large quantities of cooking oil

Small amounts of oil-contaminated food are fine, but large volumes of cooking oil slow decomposition significantly by coating food particles and preventing microorganisms from accessing them. Used cooking oil can be reused, donated, or checked for local oil collection services.

When in doubt: the Bokashi option

If you want to compost meat, dairy, cooked food, and other difficult organics, a Bokashi fermentation system is your best bet. It uses beneficial microorganisms (EM — effective microorganisms) to ferment food waste rather than decompose it. The fermented output is buried in soil where it completes decomposition quickly. See our complete guide to Bokashi composting for more detail.

Looking to reduce your waste, live more sustainably, and finally understand composting? Check out our comprehensive e-book, which has everything you need to know here.

Frequently Asked Questions

Can you compost cooked rice?

In small quantities, yes. Large amounts of cooked rice can become a breeding ground for bacteria and attract pests in open bins. Better to add it to a sealed tumbler or Bokashi system.

Can you compost bread?

Bread attracts pests in open outdoor bins. Small amounts buried deep in the pile are generally manageable, but for larger quantities, use a sealed tumbler or Bokashi system.

Can you compost weeds?

Weeds without seed heads are fine in any compost system. Weeds with seed heads should only go in hot compost (which reliably reaches 55–60°C to kill seeds) or the council green waste bin.

Can you compost dog poo?

Not in standard home compost bins. Dog and cat faeces contain pathogens that can survive home composting temperatures. Use a specialist pet waste digester or council collection instead.

Can you compost paper with colour printing?

Most modern printing inks are soy or water-based and safe to compost. Avoid glossy paper with heavy metallic inks. Standard newspaper, office paper, and kraft paper are all fine.