A heap that works twice as hard

Most gardeners think of a compost heap as a means to an end: dark, crumbly material for the borders. But a heap that is left a little less tidy than you might manage becomes one of the richest pieces of wildlife habitat in the garden. The warmth that speeds up rotting also draws in slow worms, grass snakes, frogs and a whole cast of insects, and those in turn bring the birds. You do not have to choose between good compost and a lively heap. With a little planning, you can have both.

Site it properly and build it on soil

The single most useful thing you can do is stand the heap directly on bare soil rather than on concrete or paving. That allows worms, beetles, fungi and bacteria to move up from below, and it gives amphibians somewhere to burrow when the weather turns cold. A corner beside a hedge, a wall or a shed is ideal: sheltered, shaded for part of the day and close to cover.

Aim for at least a cubic metre, roughly a metre in each direction. Anything smaller dries out and cools too quickly to rot well, and it offers little shelter. If you have the room, two bays side by side is the best arrangement by far — one for active composting, one to sit and mature.

• Base layer: a 10–15cm layer of twiggy prunings or broken-up woody stems, to let air in and water drain.
• Position: part shade is better than full sun, which dries the heap out.
• Cover: a piece of hessian, a tarpaulin or an old woollen blanket keeps heat and moisture in — but lift it now and then so blackbirds and robins can hunt through the top layer.
• Access: leave a gap on one side so you can work the heap without trampling the plants around it.

What to put in, and what to leave out

A heap that is roughly half soft green material and half tougher brown material will rot steadily without becoming a slimy mess. Vary the texture as you build: alternate a layer of green with a layer of brown, and give it a light forking every so often.

• Greens: grass clippings (in thin layers), vegetable peelings, tea leaves and coffee grounds, spent annuals, annual weeds that have not set seed.
• Browns: torn cardboard, scrunched paper, straw, dead leaves, woodchip, hedge trimmings chopped small, the cardboard tubes from inside toilet rolls.
• Leave out: cooked food, meat, fish, dairy, dog and cat waste, glossy magazines, perennial weed roots such as bindweed and ground elder, and any diseased plant material.

Keep the heap about as damp as a wrung-out sponge. In a dry summer, a canful of water every week or two makes a surprising difference; in a wet winter, the cover does the work for you.

The two-heap trick: hot for compost, cool for creatures

Here is the compromise that keeps everyone happy. Manage one bay briskly — turned regularly, it heats up, breaks down quickly and gives you compost in a few months. A hot heap is too warm for most residents, so treat it as the working bin.

Then let the second bay run cooler and slower. Turn it only once or twice a year, if at all, and leave the bottom and one corner completely undisturbed. This is the heap the wildlife will use: warm enough to bask against on a cool morning, cool enough to live in. If you only have room for one heap, simply leave one end alone and work the other.

Who you might find in there

Slow worms are the classic compost-heap residents. These legless lizards are entirely harmless, eat slugs and other soft-bodied pests, and seek out the gentle heat of rotting material. Grass snakes sometimes lay their eggs in a warm heap, where the steady temperature incubates them. Frogs and toads move in to shelter and hunt, and hedgehogs will root about at the edges for beetles and caterpillars. Bumblebees may nest inside a dry, undisturbed heap, and a heap left alone through winter can be a hibernation site for all of the above.

Above the surface, the birds work the heap constantly. Robins and dunnocks flick through the top layers, wrens slip in and out of the gaps, and a blackbird will happily spend an hour prospecting for leatherjackets and worms.

Turning, timing and handling with care

If you want to keep your residents, do not turn the heap in the middle of summer, when eggs and young are most vulnerable, or in the depths of winter, when frogs and slow worms are dormant inside it. Late spring and early autumn are the safest windows.

• Work in sections rather than emptying the whole heap at once, so anything you disturb has somewhere to retreat to.
• Lift material with a fork rather than driving it in — slow worms can shed their tails if handled, and amphibian skin is delicate.
• Wear gloves and wash your hands afterwards, especially if you have been handling material that might have been visited by rodents.
• Check the heap before you leave it for the winter, then leave it be until spring.

A heap treated this way is never quite finished, never quite tidy, and all the better for it. You get your compost, the garden gets a warm, damp, generous refuge — and on a mild February morning you may find a slow worm coiled on the lid, which is reward enough.