What You Can and Can't Compost

The short version: most raw kitchen and garden waste can go in your compost bin, and the few things that cause trouble are easy to remember. If it once grew and it isn't cooked, greasy or seeding, it can almost certainly be composted. The problems come from cooked food, meat and dairy (which bring rats and flies), and from a handful of plant materials that spread disease or weeds.

Here is the at-a-glance list, then the detail and the reasons behind each one.

Yes, compost these: veg and fruit peelings, tea, coffee grounds, grass clippings, soft prunings, cardboard, paper, egg boxes, dry leaves, straw.

Yes, but with a little care: crushed eggshells, citrus, onion, wood ash, soft annual weeds.

No, keep these out of a normal bin: cooked food, meat, fish, dairy, dog and cat mess, diseased plants, perennial weed roots, seeding weeds, coal ash, glossy or plastic-coated card.

If you are new to all this, it helps to read how to make compost alongside this list, because what you add is only half the story — getting the balance of "greens" and "browns" right is what turns a slimy bin into crumbly, sweet-smelling compost.

Greens to add

"Greens" are the soft, moist, nitrogen-rich materials. They are the fuel that gets your heap warm and active. On their own they turn to a wet, smelly sludge, so they always need balancing with browns (more on those below).

Add freely:

• Vegetable and fruit peelings — the backbone of most home compost. Carrot tops, potato peelings, apple cores, the soft outer leaves of a cabbage.
• Grass clippings — brilliant activator, but add them in thin layers mixed with browns. A thick wedge of fresh clippings turns into a stinking, airless mat.
• Coffee grounds and tea — fine to compost in moderation. Despite their reputation, coffee grounds are not a miracle plant feed; they are simply a useful green that composts well. Loose tea is fine; check teabags, as many UK brands still use plastic in the bag — tear them open or compost only the leaves.
• Soft prunings and spent plants — finished bean plants, deadheaded flowers, bolted lettuce, the haulm from your potatoes (if healthy).
• Young, soft hedge trimmings and nettles — nettles in particular are a superb activator.

Browns to add

"Browns" are the dry, woody, carbon-rich materials. They give the heap structure, let air in, and soak up the moisture from all those greens. Most beginners do not add nearly enough.

Add freely:

• Cardboard — one of the best and most plentiful browns. Tear up delivery boxes and toilet-roll tubes; scrunch it so it does not flatten into airless sheets. Remove any plastic tape first.
• Paper — newspaper, plain printer paper and shredded documents. Scrunch or layer it loosely.
• Egg boxes — the moulded paper-pulp kind are ideal: brown, absorbent and full of air pockets.
• Dry autumn leaves — fine in small amounts. If you have a big pile, they are better made into leaf mould on their own, as they rot down slowly and differently from the rest.
• Straw and woody prunings — chopped or shredded so they break down in a sensible timeframe. Thick woody stems can take years whole.

Browns are the thing you reach for whenever the bin looks wet or smells. Keeping a bag of torn cardboard next to the bin makes this effortless.

Add with a little care

These are fine to compost, but with a caveat worth knowing.

Crushed eggshells. You can add eggshells, but be honest about what they do: very little, very slowly. Eggshells are almost pure calcium carbonate and break down extremely slowly — you will often still find recognisable fragments in finished compost a year later. They are not a quick fertiliser, they do not meaningfully deter slugs (the "sharp barrier" idea largely fails in damp UK conditions), and they will not cure blossom end rot, which is a watering and calcium-uptake problem, not a lack of calcium in the soil — see blossom end rot for the real fix. Crush them finely if you do add them, and treat them as a minor soil conditioner rather than a magic ingredient. There is more honest detail in our guide to eggshells in the garden.

Citrus and onion. Perfectly compostable in moderation. Citrus peel is acidic and slow to rot, so chop it small and do not tip a whole bowl of marmalade peelings in at once. The old worry that they "kill" a heap is overstated for a normal mixed bin — just keep them as a modest part of the mix. (In a dedicated wormery, go easier, as worms genuinely dislike large amounts of citrus and onion.)

Wood ash. Ash from untreated wood or logs can be added sparingly — a light scattering, not barrowloads. It is alkaline and adds some potash, but too much will raise the pH and unbalance things. Never add coal or smokeless-fuel ash (see below).

Non-seeding annual weeds. Soft young weeds like chickweed, fat hen and groundsel are excellent green material — as long as they have not gone to seed. A cold home heap rarely gets hot enough to kill weed seeds, so anything flowering or seeding is a no.

Do NOT put in a normal bin

These cause real problems in an ordinary open heap or "dalek" bin. Most have a sensible home elsewhere (see the next section).

• Cooked food, meat, fish and dairy. The big one. These attract rats, mice and flies, and cause foul smells as they rot. A standard cold compost bin is not the place for last night's dinner. Raw veg peelings are fine; anything cooked, greasy or animal-based is not.
• Dog and cat faeces (and cat litter). These can carry parasites such as toxoplasma and roundworm that ordinary composting will not destroy. Keep them out of any compost destined for food crops. (Chicken and other herbivore manures are a different matter — see chickens and your vegetable garden.)
• Diseased plant material. Anything with blight, white rot, clubroot or persistent mildew should not go in — a cold heap will not kill the pathogens and you will spread the problem next year. Bin it or use council green-waste collection, which composts at high temperatures.
• Perennial weed roots and seeding weeds. Bindweed, couch grass, ground elder and dandelion roots will happily regrow from a fragment. Seeding annual weeds reintroduce the seeds. Drown them in a bucket of water for a few weeks first, then compost the slurry — or send them to council green waste.
• Coal and smokeless-fuel ash. Unlike clean wood ash, these contain sulphur and heavy metals that can harm soil and plants. Never add them.
• Glossy, laminated or plastic-coated card. Shiny magazine covers, foil-lined cartons and plastic-windowed envelopes will not break down. Likewise: glass, metal, synthetic fabrics and "compostable" plastics, which need industrial composting, not a garden bin.

Where the "no" list can go instead

A "no" for your open bin is not a "no" for composting altogether. The trickier materials just need a different system:

• Bokashi. A sealed kitchen caddy that ferments waste using bran. Crucially, it can take cooked food, small amounts of meat, fish and dairy, because it pickles rather than rots them. After a couple of weeks you bury the contents or add them to a closed compost bin.
• Hot composters. Insulated bins (such as a HotBin) that reach high temperatures can safely process cooked food and kill weed seeds and many pathogens. They cost more but handle far more than a basic dalek.
• Council food-waste collection. Most UK councils now offer a kerbside food caddy. The waste goes to industrial in-vessel composting or anaerobic digestion, which gets hot enough for meat, dairy and cooked leftovers. When in doubt, this is the easy answer.

Our full guide to composting kitchen waste walks through bokashi and the caddy systems in detail, and if your existing bin already smells or attracts pests, compost problems will help you put it right.

Get the list right and the rest is mostly patience. Keep raw kitchen scraps and garden greens going in, balance them with plenty of cardboard and dry browns, divert the cooked-food and weed-root troublemakers to the systems above, and in six to twelve months you will have your own compost — which is exactly where how to make compost takes you next.