More Than a Rubbish Tip

A well-built compost heap is the hardest-working habitat in the garden. In summer, the core of a decent heap can sit at 50–60°C, while the outer edges stay cool and damp — which means a single pile offers a warm basking spot, a humid retreat and a steady supply of decaying organic matter all at once. Slow worms curl up in the heat, grass snakes have been known to lay their leathery eggs in the soft warmth, and a whole economy of beetles, millipedes, woodlice and fungi gets to work breaking everything down.

The best part is that you are not building anything exotic. You are stacking garden waste in the right order and then leaving it mostly alone.

Choosing a Spot and a Structure

Aim for a heap at least one cubic metre — roughly a metre wide, a metre deep and a metre high. Anything smaller dries out and cools down too quickly to generate heat, and it will not hold enough moisture for fungi to thrive. Two or three bays side by side are ideal, because you can fill one while the other matures.

Site it on bare soil, not concrete or paving. Contact with the ground lets worms and beetles move in from below and lets excess liquid drain away.

• Pallets wired together into a three-sided box make a cheap, airy bin that comes apart when you want to turn the contents.
• Wooden slatted bins look tidier and still allow airflow through the gaps.
• Plastic dalek bins work for composting, but they are sealed and cool, so they support far less wildlife. If you use one, leave the base open to the soil.

Leave the top open to the rain, or cover it with a loose piece of old carpet or a sheet of cardboard in very wet spells. Avoid siting the heap against a south-facing wall if it regularly bakes dry — dappled shade with some sun is better.

The Green and Brown Recipe

Everything comes down to balance. Greens are wet and nitrogen-rich; browns are dry and carbon-rich. Build in layers rather than tipping everything in at once.

• Greens: grass clippings, soft prunings, vegetable peelings, annual weeds before they seed, spent bedding plants, tea leaves and coffee grounds.
• Browns: shredded cardboard, torn paper, egg boxes, dry leaves, straw, woodchip, chopped twiggy prunings, sawdust from untreated timber.
• Extras: a sprinkle of soil or old compost every few layers introduces the microorganisms that get things going. A handful of lime-free rock dust or a few comfrey leaves will speed things along.

A workable rule is one bucket of greens to two or three buckets of browns, layered like a lasagne. Keep each layer to about 15–20cm. If the heap smells sour and slimy, you have too much green — fork it through and add cardboard. If it is dry and nothing is happening, water it and add grass clippings.

Keep out cooked food, meat, dairy, dog and cat waste, diseased plant material, perennial weed roots such as bindweed and ground elder, and glossy printed card. These attract rats or cause problems you will spend months fixing.

Who Moves In, and Why

A layered heap that is turned occasionally and left alone in between becomes a small nature reserve.

• Slow worms are the headline residents. They are legless lizards, not snakes, and they seek out the warm, moist middle of a heap. Leave a sheet of corrugated cardboard or black plastic on top and you will often find them basking beneath it on a summer morning.
• Beetles do the heavy lifting. Rove beetles, violet ground beetles and devil's coach horses patrol the heap for slug eggs and larvae. Add a couple of short lengths of rotting log at the base for them to shelter in.
• Fungi appear as white threads through the brown layers. This mycelium is not a problem — it is the engine room of the whole process, breaking down tough lignin in twigs and cardboard.
• Hedgehogs may nest in a quiet corner of a large, undisturbed heap. Check before you fork anything over, especially between October and March.
• Birds will pick through the surface for insects, so a heap near a hedge or shrub gives them a safe escape route.

Turning, Temperature and Timing

Turn the heap every four to six weeks in spring and summer if you want compost quickly — this aerates it, restarts the heating and mixes the outer material inward. Fork the outside to the middle and the middle to the outside.

From late autumn, stop turning. A winter heap is a hibernation site, and churning it up in December evicts everything sheltering inside. Simply leave it, perhaps with a lid of cardboard to keep the worst rain off.

If you want both compost and wildlife, run two bays: turn one for speed, and leave the other completely untouched for a year as a permanent habitat pile. Stack a few logs and brash beside it and you have a corridor for amphibians and small mammals too.

When Things Go Wrong

A healthy heap smells earthy, not offensive. A sour, ammonia-like whiff means too much green and not enough air — add browns and fork it through. Fruit flies are harmless; bury fresh kitchen waste under a layer of browns to discourage them. Rats usually indicate cooked food or a heap that is too dry and open at the base; remove the food, firm the edges and keep the surrounding ground clear.

Above all, be patient. A compost heap is not a machine. Give it the right ingredients, a bit of moisture and a bit of neglect, and the wildlife will find it on its own.