Why the Contents of Your Bin Matter More in a Small Space

Composting on a balcony, in a courtyard, or at the end of a modest town garden is a different game from doing it on an allotment. There is less volume to absorb mistakes, less airflow, and far less room for a problem to sit and stew quietly for a fortnight. Get the mix right and you will have crumbly, earthy compost in a few months. Get it wrong and you will have a slimy, sour, fruit-fly-ridden disaster that puts you off the whole idea.

The good news is that most of what leaves a British kitchen is excellent composting material. What matters is knowing the short list of things that should go elsewhere, and understanding why.

Fruit and Vegetable Scraps: The Backbone of Your Bin

If it grew in a garden or a greengrocer's, it will almost certainly rot down happily. Vegetable peelings, carrot tops, apple cores, pear cores, banana skins, strawberry hulls, wilted salad leaves, the soggy ends of courgettes and aubergines — all of it is fair game.

• Tea bags and loose tea leaves, plus coffee grounds and paper filters
• Crushed eggshells, which add calcium and help stop the bin turning acidic
• Citrus peel, in moderation — fine in a traditional bin, but worms and bokashi brews can be fussy about too much of it at once
• Onion skins, garlic cloves and the papery outer layers, though these break down slowly
• Soft or mouldy fruit and veg that has gone past edible, provided it is not covered in something else

Do tear the plastic out of teabags before they go in. Many UK bags still contain a fine mesh of polypropylene, which will sit in your compost for years and then show up in your flower beds as little ghostly threads.

Garden Waste That Earns Its Place

Small-space gardeners often have less garden waste than they expect, but what there is should be used well. Soft prunings, deadheaded flowers, spent annuals, the leafy tops of herbs you have cut back, and the contents of last year's hanging baskets will all break down readily. Autumn leaves are slower, so keep them in a separate bag or bin for a year and you will have lovely leafmould for potting mixes.

Grass clippings need care. Add them in thin layers, mixed through with something dry, or they will mat into an oxygen-free slab that stinks like a pond. A handful at a time is plenty.

Every bin needs "browns" as well as "greens". Shredded newspaper, torn-up cardboard, toilet roll tubes, plain brown envelopes, and the insides of kitchen roll are all excellent. Aim for roughly two or three parts browns to one part greens by volume. If the bin smells sweet and rank, you need more browns. If it is bone dry and nothing is happening, add something damp and green.

Cooked Food, Meat and Dairy: Keep Them Out

This is the rule most new composters bump up against, and it is worth understanding rather than simply obeying. Cooked food, meat, fish, bones, fat, oils, gravy and dairy products all decompose, but they do so in a way that attracts rats, mice, foxes and flies. In a small garden or on a balcony, where a bin sits close to the house, that is a genuine problem rather than a theoretical one. The smells are stronger, the pests bolder, and you cannot simply move the heap to the far end of a field.

If you want to compost cooked leftovers, look at a bokashi bin instead. It ferments everything, including meat and dairy, in a sealed container that fits under the sink. The resulting pre-compost can then be buried in a planter or added to a conventional bin, where it breaks down quickly.

Diseased Plants, Weeds and Pet Waste

Some things should never go in a home bin, however tempting it is to make the pile bigger.

• Diseased material — tomato plants with blight, potato haulms with blight, brassica roots with clubroot. Home heaps rarely get hot enough to kill the pathogens, so you simply spread the problem back onto your beds.
• Perennial weeds — bindweed, ground elder, couch grass, dandelion roots and creeping buttercup. Even a small fragment will regrow. Drown them in a bucket of water for a few weeks first if you want to use them.
• Weeds in seed — anything with seed heads attached, unless you are absolutely certain your heap reaches a reliable 60°C.
• Dog and cat faeces, and used cat litter — these can carry parasites and pathogens that pose a risk to people, particularly in a garden where children play or where you grow edibles.
• Treated, painted or varnished wood — the chemicals do not break down and will leach into your finished compost.
• Glossy printed card, sticky labels, nappies, and plastic of any sort, including the so-called compostable bioplastics, which need industrial conditions to break down properly.

Getting the Balance Right in a Tight Space

Small bins dry out and cool down faster than big heaps, so give them a little more attention. Chop scraps small with a knife or scissors — more surface area means faster rot. Keep a lidded caddy in the kitchen and empty it every couple of days rather than letting it brew. Turn the contents with a fork every week or two if you can reach in easily, and keep the lid on to hold warmth and keep rain out.

Squeeze a handful of the mix. It should feel like a wrung-out sponge: damp, not dripping. That single test will tell you more about your bin's health than anything else. Do that, keep the wrong things out, and even the smallest London balcony bin will reward you with compost worth having.