Starting a compost bin is one of the most satisfying things you can do for your garden. But knowing what to put in — and what to leave out — makes the difference between rich, crumbly compost and a soggy, smelly disaster. Here’s everything you need to know.
The Golden Rule: Greens and Browns
Good compost is all about balance. You need a mix of two types of material:
- Greens — nitrogen-rich, wet or fresh materials that feed the microbes doing the hard work
- Browns — carbon-rich, dry materials that provide structure and airflow
Aim for roughly one part greens to two parts browns by volume. Too many greens and your compost will be slimy and smelly. Too many browns and it’ll be dry and slow to break down. Get the balance right and you’ll have dark, earthy compost in as little as three months.
What to Put in a Compost Bin
Greens (Nitrogen-Rich)
These are your workhorses — they break down quickly and generate the heat that speeds up composting.
- Fruit and vegetable peelings and scraps
- Tea leaves and coffee grounds (paper filters too)
- Fresh grass clippings
- Fresh garden prunings and plant trimmings
- Annual weeds (before they seed)
- Houseplant trimmings
- Soft green leaves
- Crushed eggshells (these also add calcium)
- Cut flowers past their best
Browns (Carbon-Rich)
Browns slow things down in the best possible way — they keep the compost aerated and stop it turning to mush.
- Cardboard and corrugated packaging (torn into pieces, no tape)
- Egg boxes — ideal for seed starting; fill each cup with compost, sow your seeds, and when ready, separate the cups and plant directly into the ground. The cardboard breaks down naturally in the soil so roots are never disturbed.
- Newspaper and plain paper (scrunched up)
- Dry autumn leaves
- Straw and hay
- Wood chippings and sawdust (from untreated wood)
- Dry plant stems
- Paper bags and paper towel tubes
- Brown paper bags
A Note on Cardboard
Cardboard is your best friend in a compost bin. It adds bulk, soaks up excess moisture, and breaks down surprisingly fast. Tear it into pieces roughly the size of your hand and mix it through the greens. If you’re drowning in delivery boxes (who isn’t?), your compost bin will thank you for them.
What Not to Put in a Compost Bin
Some things will slow your compost down, attract pests, or create unpleasant smells. Keep these out of a standard compost bin:
- Cooked food — attracts rats and other pests
- Meat and fish — same problem, and it smells
- Dairy products — butter, cheese, milk
- Diseased plants — disease can survive the composting process and spread when you use the compost
- Perennial weeds — bindweed, ground elder, couch grass; these will survive and spread
- Weeds that have already seeded — unless your compost gets very hot (above 60°C), seeds will survive
- Cat and dog waste — hygiene risk
- Glossy or coloured paper — the inks and coatings don’t break down well
- Coal ash — harmful to plants (wood ash in small amounts is fine)
- Treated wood — sawdust or chippings from treated, stained or painted wood
Our approach: We use a bokashi bin in the kitchen for all cooked food, meat, dairy and fish scraps. After around two weeks of fermentation, the pre-compost goes straight out into the garden compost bin to finish breaking down. It’s the neatest system we’ve found — nothing smelly on the worktop, nothing wasted, and the outdoor bin gets a regular boost of nutrient-rich material. If you want to compost a wider range of food waste without attracting pests, a bokashi bin paired with an outdoor composter is hard to beat.
How to Layer Your Compost Bin
Think of your compost bin like a lasagne — layers work better than dumping everything in at once.
- Start with a layer of browns — a few inches of cardboard or dry leaves at the base helps with drainage and airflow
- Add a layer of greens — kitchen scraps, grass clippings, soft garden waste
- Cover with browns — this is important; always finish with a brown layer to reduce smells and deter flies
- Repeat — keep alternating greens and browns as you add material
Every couple of weeks, give your compost a turn with a garden fork to aerate it and mix the layers. This speeds up decomposition noticeably.
Our Top Pick
HOTBIN Mini Composter & Plinth Bundle
Hot composting for smaller gardens & patios
The HOTBIN Mini turns kitchen and garden waste — including cooked food, bones and fish scraps — into rich compost up to 32 times faster than a traditional bin. Reaching 40–60°C, it works year-round without odours or pests, and fits neatly on a patio, gravel or paved surface. The plinth raises it to collect nutrient-rich liquid fertiliser from below.
Bundle includes
How Long Does Composting Take?
This depends on what you’re composting and the type of bin you’re using:
- Standard open compost bin — 6 months to a year
- Tumbling composter — 6–8 weeks with regular turning
- Hot composter (e.g. HOTBIN) — as little as 30–90 days
- Worm farm (vermicomposting) — ongoing; harvest worm castings every few months
- Bokashi — 2 weeks to ferment indoors, then transfer to your outdoor compost bin to finish breaking down (our preferred kitchen-to-garden system)
Warmer weather speeds things up considerably — summer compost will be ready faster than a batch started in October.
How Do You Know When Compost Is Ready?
Finished compost looks and smells like dark, crumbly soil. It should have an earthy smell — not rotten or eggy — and you shouldn’t be able to identify individual pieces of the original material. If it’s still lumpy and you can see identifiable food scraps, give it more time.
Run it through a garden sieve if you want a fine texture for seed sowing. Anything that doesn’t pass through can go back into the bin for another round.
Troubleshooting Common Composting Problems
It smells bad
Usually means too many greens and not enough airflow. Add more browns — torn cardboard works well — and give it a turn.
It’s not breaking down
Too dry, or too many browns. Add some fresh greens and a splash of water, then turn.
There are flies
You’re adding food scraps without covering them with browns. Always finish with a layer of cardboard or dry leaves.
It’s slimy
Too wet and too many greens. Add dry browns and aerate well.
There are rats
Avoid adding cooked food, meat, or dairy. Make sure your bin has a secure lid and sits on a rat-proof mesh base if possible.
What to Do With Finished Compost
Once your compost is ready, put it to work. Dig it into beds before planting, use it as a mulch around established plants, or mix it into potting compost for containers. A single barrowful spread across a raised bed will transform the soil structure over a season.
Ready to start composting? Take a look at our guide to the best compost bins for UK gardens — from fast-acting hot composters to beautiful wooden bins that earn their place in the garden.
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