Composting is the one garden job that pays you twice: it disposes of waste you would otherwise cart to the tip, and it produces the best soil improver money cannot easily buy. Yet plenty of gardeners give up after a first heap turns into a slimy mess or a dry pile of intact twigs. Almost every composting failure comes down to the same two or three fixable causes.
Greens and browns, without the mystique
Composting guides can make the process sound like chemistry homework. In practice you only need one idea: mix soft, wet, nitrogen-rich material ("greens") with dry, tough, carbon-rich material ("browns") in roughly equal volumes.
- Greens: grass clippings, vegetable peelings, salad leaves, annual weeds, coffee grounds, fresh plant trimmings, urine-soaked pet bedding from vegetarian animals (rabbits, guinea pigs).
- Browns: cardboard (torn up), scrunched paper, egg boxes, autumn leaves, straw, woody prunings (chopped small), wood chip, sawdust from untreated timber.
Greens supply nitrogen and moisture; browns supply carbon and, crucially, structure — air pockets that keep the heap breathing. Most household heaps fail because they are nearly all greens (grass and peelings) with no browns. The habit that fixes this permanently: keep a box of torn cardboard next to the bin and add a couple of handfuls every time you tip in kitchen waste.
What to include — and what to leave out, honestly
Some exclusions on traditional lists are overcautious; others are genuinely important.
Fine to add
- All raw fruit and vegetable waste, including citrus and onions in normal quantities
- Tea leaves and coffee grounds (check tea bags are plastic-free)
- Eggshells, crushed — they break down slowly but harmlessly
- Annual weeds before they set seed
- Torn cardboard, paper and autumn leaves
Leave out of an ordinary cold heap
- Cooked food, meat, fish and dairy. Not because they will not rot — they will — but because they attract rats and flies in an open heap. If you want to compost cooked food, use a sealed hot composter or a bokashi bin first.
- Perennial weed roots: bindweed (Calystegia sepium), couch grass (Elymus repens), ground elder (Aegopodium podagraria) and dandelion tap roots survive a cool heap and come back to haunt you. Drown them in a bucket of water for a month, or bag them to rot separately, before composting the sludge.
- Weeds in seed. A cold heap does not kill most seeds; you will sow them wherever you spread the compost.
- Diseased material such as blight-infected tomato or potato foliage, rose leaves with black spot, or anything with white rot or clubroot. Council green waste collections are hot-composted commercially and will deal with these safely.
- Dog and cat faeces, glossy laminated card, and ash from coal.
Choosing a bin
The container matters less than what goes in it, but each type suits a different garden.
| Type | Best for | Notes |
|---|---|---|
| Plastic "dalek" bin | Small gardens, kitchen and light garden waste | Cheap, tidy, retains warmth and moisture; hard to turn; stand it on soil so worms can enter |
| Pallet bays (two or three) | Larger gardens with real volume of waste | Free to build; multiple bays let you fill one while another matures; turning is easy |
| Insulated hot bin | Households wanting to compost cooked food fast | Reaches 40–60°C, kills seeds and pathogens, produces compost in months; needs regular feeding and attention |
| Wormery | Flats, courtyards, kitchen waste only | Composting worms turn peelings into rich casts and liquid feed; keep frost-free in winter; no grass or woody waste |
Whatever you choose, site it on bare soil where possible, in light shade rather than baking sun, and somewhere you will actually walk to in the rain — a bin by the back door gets fed; a bin behind the shed gets forgotten.
To turn or not to turn
Both approaches work; they just run at different speeds.
Turning — forking the contents out and back in, or into an adjacent bay — mixes greens and browns, reintroduces air, and reheats the heap. A heap turned every few weeks through the warmer months can produce usable compost in four to six months.
Not turning works too. Fill the bin, keep the mix roughly balanced as you go, put the lid on and wait. Worms, fungi and time do the work over twelve to eighteen months. This is a perfectly respectable method for anyone who does not fancy heavy forking; the compost from a slow cold heap is every bit as good.
A worthwhile middle path: turn the heap once, in spring, and otherwise leave it alone.
Moisture: the wrung-out sponge test
A heap should feel like a wrung-out sponge — clearly damp, but not dripping when squeezed. Too dry and decomposition simply stops (common in daleks in a hot summer, and in heaps heavy on cardboard); water it with a can or add fresh grass clippings. Too wet and it turns airless and smelly (common in open heaps in winter); mix in dry browns and cover the top with a lid, carpet offcut or thick cardboard to keep rain out. Checking moisture once a month solves most problems before they start.
How long it really takes
Ignore any promise of compost in six weeks. Realistic timings in a UK garden:
- Hot bin, actively managed: 3 months or so.
- Regularly turned open heap or bays: 4–6 months across the growing season.
- Cold dalek, filled gradually and left: 12–18 months.
- Leafmould (autumn leaves composted separately in a wire cage or bin bags with holes): 1 year for mulch, 2 years for a fine, crumbly soil conditioner.
A practical rhythm for a single dalek: fill it over spring and summer, stop adding in autumn, let it finish over winter, and empty it the following spring while starting the cycle again. Two bins make this easier — one filling, one finishing.
Troubleshooting the two classic failures
Slimy, smelly sludge
Too many greens, too little air — nearly always a bin fed on grass clippings and peelings alone. The smell (ammonia or rotten eggs) means it has gone anaerobic. Fork in a generous volume of torn cardboard, scrunched paper or straw, mixing thoroughly, and it will sweeten within a couple of weeks.
Dry, dusty and nothing happening
Too many browns and too little moisture — a heap of woody prunings and cardboard can sit unchanged for years. Water it well, add greens (grass clippings are ideal), and chop woody material smaller; anything thicker than a pencil is best cut up or run over with a mower.
Two lesser complaints: clouds of tiny fruit flies are harmless and vanish if you bury kitchen waste under a layer of browns; ants nesting in the heap mean it is too dry — water it and they will move on. Rats are only a serious risk where cooked food or grains go in, or where a heap is never disturbed; a stab with a fork every week or two is a good deterrent.
When it is ready, and how to use it
Finished compost is dark brown, crumbly, smells pleasantly earthy, and the original ingredients are no longer recognisable — apart from the odd twig, eggshell or avocado stone, which you can sieve out or simply return to the next heap. It does not need to be perfectly fine-textured to be useful.
- Mulch: spread 5cm deep on beds and around (not touching) shrubs and fruit in March or April, or in autumn. Worms will incorporate it — no digging needed.
- Planting: a few handfuls in a planting hole, mixed with the soil, gives new perennials, roses and shrubs a strong start.
- Vegetable beds: a barrowload per few square metres in spring feeds hungry crops such as courgettes, beans and potatoes.
- Not as seed compost: garden compost is too rich and variable for seed sowing on its own; use it for mature plants and buy or mix a finer, low-nutrient medium for seeds.