Building a Simple Compost Heap Outdoors

Why a compost heap belongs in every garden

There is something quietly satisfying about a compost heap. It turns the leftovers of your garden and kitchen into dark, crumbly gold that feeds the soil, holds moisture, and helps everything from roses to runner beans grow stronger. In rural places, where gardens, hedgerows, and smallholdings often meet, a heap also keeps useful material on site instead of sending it away in a trailer. You do not need an expensive bin or a degree in soil science. A simple outdoor heap, built in layers and given a little attention, will do the job beautifully.

Choosing the right spot

Pick a level patch of ground that is easy to reach all year round, ideally not more than a short walk from the kitchen door. A spot in dappled shade is ideal: full sun can dry the heap out, while deep shade keeps it cold and sodden. In the UK, rain is usually plentiful, so an open heap is fine, but a little shelter from the prevailing wind will stop it blowing apart.

Make the heap about one metre wide and one metre tall, and build it up as materials arrive. A two-bay system is the classic approach: fill one side, then turn the contents into the second bay to aerate it. Sit it directly on soil, not concrete, so worms and microbes can move in from below. Avoid placing it against a fence or tree trunk, and keep it clear of any hedgehog hibernation spots.

The golden rule: alternate greens and browns

Good compost is a balance between two kinds of material. Greens are wet, nitrogen-rich and rot quickly: grass clippings, vegetable peelings, tea leaves, coffee grounds, nettles, comfrey, and herbivore manure. Browns are dry, carbon-rich and give the heap structure: cardboard, newspaper, straw, autumn leaves, woodchip, sawdust, egg boxes, and torn-up toilet roll tubes.

Aim for roughly two to three parts browns to one part greens by volume. In practice, that means building the heap in thin layers. Start with a 15cm layer of browns, then a 10cm layer of greens, then a sprinkle of garden soil or old compost. Repeat until the heap is about a metre high. Do not compact it; a gentle mix with a fork is enough. The layers will create air pockets, which is exactly what the microbes need.

• Greens: grass clippings, fruit and veg scraps, plant trimmings, annual weeds before they seed, manure from horses, cows, rabbits, and chickens.
• Browns: cardboard (tape removed), newspaper, straw, dry leaves, wood shavings, bracken, and chopped twigs.
• Activators: a handful of soil, a few nettles, or a thin layer of finished compost to introduce more organisms.

Turning and moisture: the wrung-out sponge test

Keep the heap as moist as a wrung-out sponge. Squeeze a handful: it should feel damp but not drip. If it is dry, water it with a can or add more greens. If it is soggy, fork in more browns and turn it. In a hot summer, you may need to water every week or two.

Turning the heap occasionally adds oxygen, which speeds up decomposition and reduces smells. Every two to four weeks is plenty for a fast heap; if you are happy to wait, turn it once a season. Use a garden fork to pull the outside material into the middle and the middle to the edges. A well-made heap will heat up to 40–60°C in the centre, then cool as it matures. Do not turn it too often, or you will lose that heat and slow the process down. If the heap is cold and slimy, it is usually too wet and too green; add browns, turn, and leave it.

What to add and what to leave out

A rural heap can take more than a suburban bin, but a few rules keep it sweet and discourage rats. Add fruit and vegetable scraps, eggshells, grass clippings in thin layers, shredded prunings, cardboard, paper, straw, and small amounts of wood ash. Avoid cooked food, meat, fish, dairy, dog or cat waste, glossy magazines, treated wood, and diseased plants. Perennial weeds such as bindweed and ground elder are best kept out unless you are sure the heap gets hot enough to kill them. If you want to compost cooked food, use a sealed wormery or a dedicated bin with a lid.

• Chop bulky items: scrunch cardboard, shred paper, and cut thick stems into shorter lengths.
• Mix grass clippings: never leave them in a thick mat; stir them through browns.
• Keep it tidy: a neat heap looks better and works better. A piece of old carpet or a tarpaulin can cover it in very wet weather, but remove it in dry spells.

Troubleshooting and sharing the harvest

Most problems have a simple fix. A smelly, slimy heap needs more browns and a good turn. A dry, inactive heap needs water and greens. A heap that never heats up may be too small; gather more material in one go, or insulate the sides with straw bales. Fruit flies are normal, but bury kitchen scraps in the middle to keep them down. If you see worms, woodlice, and fungi, your heap is working as it should.

Compost is ready when it is dark, crumbly, and smells of woodland floor. Depending on the season and how often you turn it, that can take three months to a year. Use it as a mulch around fruit bushes and perennials, dig it into vegetable beds, or sieve it for potting mixes. In a rural community, a good heap is also a conversation starter: share surplus compost with neighbours, or offer it to the village allotment. Leave a corner of the heap undisturbed over winter, and you may give a hedgehog or slow worm a safe place to shelter. A simple outdoor compost heap is one of the best bargains in gardening: free, quiet, and endlessly generous.