Why kitchen scraps deserve a place in your garden

If you cook from scratch even a few nights a week, you're probably binning a surprising amount of good stuff: onion skins, carrot tops, coffee grounds, the tired outer leaves of a cabbage. All of it is garden gold waiting to happen. Composting at home turns that waste into a dark, crumbly material that improves almost any soil — lightening heavy clay, helping sandy ground hold water, and feeding the worms and microbes that do the real work underground.

The other reward is quieter but just as real. A well-run compost bin means fewer bin bags, fewer trips to the wheelie bin, and a closed loop between your kitchen and your veg patch. You'll find it becomes a habit surprisingly quickly: the peelings go into a little caddy by the sink, the caddy goes out to the heap, and a year later those same nutrients are back in your runner beans.

Getting the green and brown balance right

Everything in the compost heap falls into one of two camps. Greens are wet, nitrogen-rich materials that rot quickly. Browns are dry, carbon-rich materials that give the heap structure and air pockets. Get the ratio roughly right and the heap will heat up, smell sweet and break down in months rather than years.

As a rule of thumb for a domestic bin, aim for about one bucket of greens to two or three buckets of browns by volume. If you're unsure, add more browns — it's the single most common fix for a struggling heap.

• Greens: vegetable and fruit peelings, tea leaves and torn-open tea bags, coffee grounds, grass clippings, spent annuals, soft hedge trimmings, nettles and comfrey leaves.
• Browns: torn cardboard (remove the tape), egg boxes, shredded paper, loo roll tubes, straw, woodchip, autumn leaves, chopped twiggy prunings, untreated sawdust.

Chop things up as you go. Scraps cut to roughly 2–5 centimetres break down far faster than a whole swede, and a quick crush of eggshells stops them sitting around intact for months.

What to add and what to leave out

A garden compost heap is not the same as a food waste bin, and a few things really are best kept out — either because they attract pests or because they carry problems you don't want to spread.

• Fine to add: fruit and veg scraps, coffee grounds and filters, plastic-free tea bags, crushed eggshells, dead houseplants, grass clippings in thin layers, hair, vacuum dust from natural fibres.
• Leave out: cooked food, meat, fish, dairy and bones (they draw rats), cat and dog faeces, disposable nappies, treated or painted wood, glossy magazines, and anything plastic-coated.
• Handle with care: perennial weeds such as bindweed and ground elder, diseased foliage from tomatoes or potatoes, and weed seeds. These are safest in a hot heap that reaches 55–60°C, or better still, kept out altogether.

If you have a lot of cooked leftovers, a sealed bokashi bin or wormery is a smarter route than an open heap. Both handle things a traditional compost pile can't, and both produce a lovely liquid feed you can dilute for pots and containers.

Air, moisture and a bit of muscle

Composting is an aerobic process, which is a fussy way of saying the microbes need oxygen. That's why a heap that's been squashed flat under wet grass clippings turns slimy and smelly, while a fluffy one full of cardboard and twigs works away quietly.

Aerate your bin every couple of weeks. With a dalek-style bin, that means lifting the whole thing off, forking the contents back in and mixing as you go — a ten-minute job that makes a real difference. With a bay system, simply turn it from one bay into the next. If you'd rather not turn it, push a broom handle or a purpose-made aerator stake deep into the middle and wiggle it about.

Moisture matters too. Squeeze a handful of the contents: it should feel like a wrung-out sponge, damp but not dripping. Too dry — usually the fault of too much cardboard in summer — and you should water it as you turn. Too wet, and you need to fold in more shredded paper or woodchip.

When it goes wrong

Most compost problems have an obvious cause, and most of them are fixable in an afternoon.

• Smells sour or like rotten eggs: too wet and too little air. Turn it, add browns, and check the base isn't sitting in a puddle.
• Smells of ammonia: too many greens. Stir in a good layer of torn cardboard.
• Nothing is happening: the heap is too dry, too cold or the pieces are too big. Water it, chop things smaller, and turn it to wake it up.
• Fruit flies or wasps: bury fresh kitchen scraps under the top layer of browns rather than leaving them exposed.
• Rats: almost always cooked food or a bin with a broken base. Keep the lid on, add no cooked scraps, and stand the bin on a sheet of sturdy mesh.

Winter slows everything down — that's normal, not a failure. The heap will tick over quietly and pick up speed again in March.

Knowing when it's ready and how to use it

Finished compost is dark, crumbly and smells of woodland floor after rain. You shouldn't be able to recognise what went in, though the odd eggshell or avocado stone is a harmless survivor. In a warm, well-turned heap you might have usable compost in three to four months; a cooler, less managed bin can take nine to twelve.

Sieve out the lumpy bits and throw them back in to finish off. Use the good stuff as a mulch around fruit bushes and perennials, fork it into the top few centimetres of a veg bed, or mix it with grit and sieved soil for potting on. A couple of centimetres spread across a bed each spring is plenty — it's a soil improver, not a fertiliser, so think of it as feeding the ground rather than the plant.

Start small if you like. One bin, one caddy, one season of paying attention to what goes in and what comes out. Your soil will tell you soon enough whether it's working, and the answer is usually written in bigger courgettes and healthier-looking brassicas.