Why a heap is worth the bother

Home composting is one of those rare gardening jobs that pays you back twice. You stop binning kitchen peelings and prunings, and in return you get a crumbly, dark material that feeds your soil, holds moisture and keeps your plants steady through dry spells. It is also the single best thing you can do for the wildlife in your garden, because healthy soil full of organic matter supports the worms, beetles, fungi and microscopic life that everything else depends on. Birds, hedgehogs and slow worms all benefit indirectly from a garden that teems below ground.

You do not need expensive kit. A heap, a bin or a bay made from old pallets will do, as long as you get the basics right. Those basics come down to three things: the right mix of materials, enough air, and enough moisture.

Getting the green and brown balance right

Composting is simply speeding up what happens on a forest floor. Microbes and larger creatures break down plant material, and they need a balanced diet to work quickly. That diet comes in two colours.

• Greens are soft, wet and nitrogen-rich: vegetable peelings, fruit scraps, grass clippings, tea leaves, coffee grounds, annual weeds before they set seed, and spent bedding plants.
• Browns are dry, tough and carbon-rich: torn cardboard, egg boxes, toilet roll tubes, scrunched paper, straw, dead leaves, and woody prunings chipped or chopped small.

Aim for roughly two parts brown to one part green by volume. This is the one ratio worth remembering, and it catches out most beginners. A heap fed on kitchen scraps alone turns into a slimy, smelly mess. A heap with plenty of cardboard stays sweet, crumbly and quick. If your bin smells sour, add browns. If it sits dry and does nothing, add greens and a splash of water.

What to leave out

A surprising amount can go in, but a few things are best kept out of a cool domestic heap.

• Cooked food, meat, fish and dairy — these attract rats and foxes and turn rancid.
• Perennial weeds such as bindweed, ground elder and couch grass roots, plus seeding weeds and diseased foliage. Most home heaps never get hot enough to kill them.
• Dog and cat faeces, and used cat litter.
• Glossy magazines, plastic tape and coated cartons — the plastic does not rot, it just shreds into litter.
• Large woody branches unless chopped or shredded; they will still be there in three years.

Teabags are worth a mention: many have a plastic seal, so tear them open and compost the leaves, or choose plastic-free ones. Citrus peel, onion skins and small amounts of bread are fine in moderation.

Siting and building the heap

Put your bin or bay somewhere level, in partial shade, and reasonably close to the kitchen door so you actually use it. Contact with the soil underneath matters, because worms and other creatures need to move in and out — so sit a plastic bin on bare earth rather than paving, or leave the base off entirely.

Size helps more than most people realise. A heap roughly one cubic metre — about a metre wide, a metre tall and a metre deep — holds heat far better than a tiny bin. If space is tight, a wormery or a couple of stacked bays will still give you good results.

Build in layers rather than tipping everything in one go. Alternate a few centimetres of greens with a few of browns, and give each layer a light sprinkle of soil or old compost. That thin sprinkle introduces extra microbes and stops the layers matting together. Chopping things up as you add them is the easiest speed-up available: a shredded cabbage stalk breaks down in weeks, a whole one in months.

Turning, moisture and the wrung-cloth test

Air is what separates composting from rotting. Turning the heap with a fork every two to four weeks moves the outside material into the middle where the action is, and pushes fresh oxygen through the whole pile. You will feel it warm up afterwards, sometimes noticeably. A well-managed heap can reach 60°C or more in the core, which is why steam on a cold morning is a good sign, not a problem.

Moisture is the other half of the equation. The ideal is often described as as damp as a wrung-out cloth — moist enough to glisten when you squeeze a handful, but not dripping. Too dry and the process stalls; too wet and the air spaces fill with water and everything goes anaerobic and smelly. In a dry summer, water the heap as you turn it. In a wet winter, leave the lid on and mix in extra cardboard to soak up the excess.

If you want to speed things along, keep a small tub in the kitchen for scraps and a stash of torn cardboard beside the bin, so adding the right balance is never more effort than adding the wrong one.

When it is ready, and how to use it

Depending on the season and how often you turn it, a batch will be finished in anywhere from two to twelve months. It is ready when it looks like dark, crumbly soil, smells earthy rather than sour, and you can no longer recognise what went in — bar the odd eggshell or avocado stone, which do no harm.

Dig the finished compost into your borders and vegetable beds, or spread it as a mulch around shrubs, fruit bushes and perennials, leaving a small gap around stems. A couple of centimetres is plenty. You can also sieve a batch and use the finer material for potting mixes and seed sowing. Anything that has not broken down goes back into the next heap to start the cycle again.

Start with one bin, get the balance and moisture right, and you will wonder why you ever put those peelings in the bin.