Why a pallet bin earns its place

No piece of garden kit repays a spare hour more generously than a compost bin made from four pallets. They are usually free — ask at a builder's yard, a bike shop or anyone expecting a delivery — and since a pallet is built to carry a tonne of bricks, a bin made from four will outlast most plastic cones. The slats let air move through the heap, which is exactly what the bacteria and fungi need, and the gaps are wide enough to fork material out when it is ready.

A standard UK pallet is about 120cm by 100cm, so four stood on edge give a bin roughly a metre square and a metre tall — around a cubic metre. That is the sweet spot: big enough to hold heat, small enough to turn with a fork.

Choosing and siting your pallets

Look for heat-treated pallets, stamped HT. Avoid anything marked MB, which has been fumigated with methyl bromide, and steer clear of pallets that have carried chemicals or unknown powders. A faint smell of pine is fine; a smell of solvent is not.

Site the bin on bare soil or grass, not paving, so worms and microbes can move in from below. A level spot in partial shade suits best: full sun dries the heap out, deep shade keeps it cold. Leave room to walk around at least two sides, because you will want to turn it. On heavy clay, fork the ground over first, or lay a few inches of twiggy prunings at the base to help drainage and airflow.

Tying it together

Stand three pallets in a U shape and tie the fourth across the open front. Lash the corners tightly with baling twine, heavy-duty cable ties or galvanised wire. Bind at the top, middle and bottom of every vertical joint — three ties per corner, twelve in all. Loop through the slats and pull hard; a bin that wobbles spills its contents every time you turn it.

For an opening front, tie the fourth pallet at the bottom only and hook the top corners with a short length of rope. Drive a wooden stake inside each corner if the pallets are flimsy, and line the inside with a couple of sheets of cardboard if the slats are widely spaced — that keeps the outer edges from drying out and stops material spilling through.

Filling it: greens, browns and the lasagne rule

Composting is a conversation between two materials. Greens are wet and nitrogen-rich: grass clippings, vegetable peelings, tea leaves, coffee grounds, annual weeds before they set seed. Browns are dry and carbon-rich: torn cardboard, newspaper, egg boxes, straw, dead leaves, woodchip, shredded twigs.

Layer them like lasagne, aiming for two or three bucketfuls of browns to every one of greens by volume. This is the most common mistake, because most gardens produce far more green material than they realise. Scatter a 15cm layer of greens, then a 20cm layer of browns, and repeat. Keep a bag of shredded cardboard by the bin and add a handful every time you empty the kitchen caddy.

• Chop bulky things up — a spade through a cabbage stalk makes a real difference.
• Never add cooked food, meat, dairy or pet waste to a cold bin; they attract rats.
• Skip perennial weeds such as bindweed, ground elder and docks unless the heap gets properly hot.

Keeping it damp as a wrung cloth

Push your hand into the middle of the heap and squeeze. It should feel like a wrung-out flannel — damp, perhaps a drop or two of dark liquid, but not dripping. If it is dry, water it with a can, layer by layer, as you turn it. If it is slimy and stinks, there is too much green and not enough air: fork it over and add a barrowful of shredded cardboard or straw.

A lid made from a piece of tarpaulin, a sheet of corrugated iron or a fifth pallet laid on top keeps the worst of the rain out and holds warmth in. Weight it with a brick so it does not blow off in a gale.

Turning, timing and the wildlife bonus

Turn the heap every three or four weeks in summer and every six to eight in winter. The easiest method is to lift the bin off, fork the contents into a new pile beside it, and rebuild the bin around the fresh heap — you will be surprised how much it shrinks. A well-built cubic metre bin can reach 50–60°C within a fortnight, hot enough to steam on a cold morning and to kill most weed seeds.

Left alone, a cold heap takes a year or so but still works, and it becomes a hotel for wildlife: slow worms in the base, beetles and centipedes in the middle, a robin or wren watching from the fence for anything that moves. Come spring, when the contents are dark, crumbly and smell of woodland floor, with no recognisable peel or stalk, it is ready. Sieve the lumps back into the next heap and spread the rest where the beans will go.