Why a compost heap earns its place in a wildlife garden

A well-built compost heap is one of the hardest-working features in a British garden. It turns kitchen peelings and prunings into dark, crumbly leaf mould, and while it is quietly getting on with that job, it becomes a warm, damp, insect-rich habitat for everything from hedgehogs to slow worms. The trick is to build it with wildlife in mind from the start, rather than treating it purely as a waste disposal unit.

Site your heap on bare soil, not on paving or concrete, so worms and beetles can move up from below. A spot in dappled shade is ideal — full sun dries a heap out, deep shade keeps it cold and soggy. Leave a corridor of rough grass or a log pile nearby so creatures have cover as they travel to and from the heap.

Getting the greens and browns right

The classic rule holds: roughly two parts brown material to one part green. Browns are carbon-rich and dry; greens are nitrogen-rich and wet. Too many greens and you get a slimy, smelly mess; too many browns and nothing much happens for months.

• Greens: grass clippings (in thin layers, never a thick mat), vegetable peelings, tea leaves, coffee grounds, annual weeds before they set seed, soft prunings, comfrey leaves, spent bedding plants.
• Browns: autumn leaves, shredded cardboard and plain paper, egg boxes, straw, woodchip, chopped twiggy prunings, dead stems, the contents of old hanging baskets.
• A sprinkle of soil or old compost every few layers introduces the micro-organisms that get the process going.

Skip cooked food, meat, fish, dairy, dog and cat faeces, diseased plant material, perennial weed roots such as bindweed and ground elder, glossy magazines, and anything treated with preservative. These attract rats, spread disease, or simply refuse to rot.

Build it big enough to heat up, small enough to manage

Aim for a heap at least a metre square and a metre high. That mass is what allows the centre to reach the sort of temperatures that kill weed seeds and speed everything along. If space is tight, two plastic or wooden bins side by side work well: fill one, leave it to finish, then turn it into the other.

Start with a base layer of coarse twigs, broken stems or scrunched-up cardboard about 15cm deep. This drains excess water and lets air in from below, and it creates exactly the kind of open, sheltered nooks that slow worms and frogs love. Add materials in mixed layers rather than dumping everything in one go, and chop anything thick with the edge of a spade — smaller pieces rot faster and give more surface area for invertebrates to work on.

Keep it damp and breathing

The heap should feel like a wrung-out sponge. Squeeze a handful from the middle; if it drips, it is too wet — fork in more shredded cardboard and turn it. If it crumbles dry, water it with a can, preferably rainwater from the butt.

Cover the top with a piece of old hessian, a folded tarpaulin or a layer of straw to hold moisture in and stop rain turning it to sludge. Turn the heap when it cools down and looks finished on the outside, roughly every six to eight weeks in spring and late summer. As you turn, mix the outside to the middle and break up any clumps.

If you want to speed things along, a handful of nettles, comfrey or a diluted comfrey tea poured over the layers acts as an activator without any need for bought products.

Leave the bottom alone for the residents

This is the part that matters most for wildlife. The lower third of a compost heap stays cool, damp and full of worms, slugs and beetles — a larder and a bed in one. Hedgehogs often choose the base of a heap to hibernate, bedding down from around November to March. Slow worms, being legless lizards rather than snakes, are drawn to the warmth and to the slugs and worms within easy reach, and grass snakes will sometimes lay eggs in the rotting vegetation in midsummer.

• Do not fork over the bottom third between October and March, when a sleeping hedgehog will not wake in time to escape.
• Avoid turning the heap at all in hard frost or during a summer heatwave, when slow worms and grass snakes may be using it.
• Lean a plank or log against one side to create a natural ramp, so anything that wanders in can find its way out again.
• Keep a shallow dish of water nearby — hedgehogs and birds both need it, especially in dry spells.

Harvesting without evicting

Use your compost in spring and early autumn, when the heap is at its least occupied. If you must dig into the base, do it gently, working from one end so anything sheltering can retreat to the other. Leave a bucketful of the oldest material behind to kick-start the next heap.

Stack a few rotting logs beside the bins, and let a patch of nettles or brambles grow nearby. Between them, the heap and its surroundings become a year-round home rather than a temporary stopover — and you get better compost for it, too.