How to Fix Common Composting Problems (Australia Guide)

Even experienced composters run into problems occasionally. The good news is that composting is a remarkably forgiving process — almost any problem can be identified and corrected. This guide covers the most common issues Australian home composters face, why they happen, and what to do.

Problem 1: My compost smells bad

Smells like rotten eggs or sewage

This indicates anaerobic conditions — the pile has become too wet and compacted, cutting off oxygen supply. Anaerobic bacteria produce hydrogen sulphide (the egg smell) as a by-product.

• Fix: Turn the pile thoroughly to introduce oxygen. Add a generous layer of dry browns (torn cardboard, dry leaves). If the pile is very wet, leave it partially uncovered in dry weather to allow moisture to evaporate.

Smells like ammonia

An ammonia smell indicates too much nitrogen — the greens-to-browns ratio is off.

• Fix: Add carbon-rich browns (cardboard, straw, dry leaves) and mix well. The nitrogen is releasing as gas rather than being fixed into the compost — balancing with carbon will stop this.

Problem 2: My compost isn’t breaking down

A pile that doesn’t seem to be decomposing is usually caused by one of four factors: too dry, not enough nitrogen, too much woody material, or insufficient airflow.

• Too dry: Water the pile and cover to retain moisture. It should feel like a wrung-out sponge.
• Not enough nitrogen: Add fresh greens (food scraps, lawn clippings, coffee grounds).
• Too much woody material: Large sticks and branches take years to break down. Remove them or chip them first.
• No airflow: Turn the pile. A pile that hasn’t been turned becomes compacted and loses the oxygen needed for aerobic decomposition.

Problem 3: My compost pile has pests

Flies and fruit flies

Fruit flies are attracted to exposed food scraps on the surface.

• Fix: Always bury food scraps under a layer of brown material. Cover the pile with a breathable cover or lid. Avoid adding cooked food to open piles.

Rats and rodents

Rats are attracted to meat, bread, dairy, and cooked food scraps.

• Fix: Remove meat, dairy, and cooked food from your compost entirely. Use a bin with a secure base or sit it on a metal mesh. Rodent-proof the sides with chicken wire if needed. Switch to a sealed tumbler compost bin.

Ants

Ants in a compost pile indicate it’s too dry.

• Fix: Water the pile. Ants don’t generally cause problems in compost — they can actually help aerate it — but their presence is a sign you need more moisture.

Problem 4: My compost is too wet and slimy

• Fix: Add large amounts of brown material (torn cardboard, dry straw, dry leaves). Mix well. If the pile is very waterlogged, create a temporary cover to prevent rain adding more moisture, and allow airflow to dry it out.

Problem 5: My compost isn’t getting hot

If you’re trying to hot compost and the pile won’t heat up:

• Check the volume — it needs to be at least 1 cubic metre
• Add more nitrogen (fresh greens) — nitrogen is the fuel for microbial activity
• Check moisture — a dry pile won’t generate heat
• Turn it — introducing oxygen reignites microbial activity
• Be patient — a new pile can take a week to start heating

Problem 6: My finished compost has large uncomposted chunks

This is normal. Large pieces of woody material, avocado skins, corn cobs, and similar items take longer to break down than soft food scraps.

• Fix: Sieve the finished compost through a mesh screen. Return the larger chunks to the active pile to continue composting. Use only the fine, dark compost for your garden.
  

Quick-reference troubleshooting table

Problem	Likely cause	Fix
Smells like rotten eggs	Too wet/anaerobic	Add browns, turn, aerate
Smells like ammonia	Too much nitrogen	Add browns, mix well
Not breaking down	Too dry, no nitrogen, or no air	Add water, greens, or turn
Fruit flies	Exposed food scraps	Bury scraps, add brown cover
Rodents	Meat/dairy in pile	Remove problem materials, seal bin
Too wet/slimy	Too many greens, excess rain	Add browns, cover from rain
Not getting hot	Too small, too dry, no nitrogen	Check size, moisture, greens
Large chunks remaining	Normal; woody items break down slowly	Sieve and return chunks to pile

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

Is a smelly compost bin a problem?

A mild earthy smell is normal. Strong odours — rotten eggs or ammonia — indicate something is out of balance, but they’re fixable. See the fixes above.

Can I still use compost that had a bad smell?

Usually yes, once the problem is fixed and the pile is balanced again. Allow a further few weeks of active composting after correcting the issue before harvesting.

My compost is full of ants — is this a problem?

Ants in compost are generally harmless and can help aerate the pile. However, they indicate the pile is too dry. Water it and the ants will likely move on.