Why Pallets Make the Ideal Compost Bin

Walk around any smallholding and you will find a stack of pallets behind the barn, waiting for a purpose. They are sturdy, free, and already built with gaps that let air into a heap — exactly what a compost bin needs. A four-pallet bin takes under an hour to assemble, costs nothing but a handful of screws, and holds roughly a cubic metre. That volume matters: it is the smallest heap that reliably heats up, and a hot heap breaks down in a fraction of the time a cold one does. Build two bins side by side if you can — one to fill, one to turn into.

Choosing and Checking Your Pallets

Not every pallet is safe for the garden. Look for the stamp on the corner block. HT means heat-treated, which is fine. MB means the wood has been fumigated with methyl bromide — leave those well alone. Unstamped pallets are usually fine, but avoid anything that has carried chemicals, paint tins or unknown powders.

Give each pallet a once-over:

• Check for rotten or split slats and pull out loose nails with a claw hammer.
• Rasp down splintered top edges.
• Reject anything painted, oil-stained or chemically smelly.
• Standard pallets are 1200mm by 1000mm, giving a bin close to a metre square.

Keep the slats running horizontally, so they hold the material back once the heap is full.

Siting the Bin

Pick a level spot in some sun, easy to reach with a wheelbarrow. Avoid the foot of a slope where water gathers, and keep clear of tree roots that will happily invade a damp heap. On heavy clay, fork the ground over first.

Lay a double thickness of plain cardboard over the footprint, overlapping the sheets generously. It smothers weeds, stops the heap sitting in a puddle, and feeds carbon and worms into the base as it rots. Damp it and weigh it down with a few bricks until the frame goes up.

Putting the Four Sides Together

Stand two pallets at right angles on the cardboard and screw them together at the corner. The cleanest method is to screw a short length of 75mm by 75mm timber into the corner of each pallet first, then screw the two posts together. Failing that, drive four long coach screws per corner, straight through one pallet's end slat into the block of the other.

Use 100mm screws or M10 bolts; anything shorter will not bite. Pre-drill the holes to stop older, drier wood splitting.

Close the square with the third and fourth pallets. Leave one side unfixed, or fix it to a pair of battens and slot it into place: a removable front panel saves a great deal of swearing when you want to turn the heap or dig out finished compost. Check the frame is square by measuring the diagonals, and bed any rocking corners with a spadeful of soil or a flat stone.

Filling the Bin

Build the heap in one go rather than adding a handful every week, which is the surest route to a cold, smelly pile. Gather your material first, then layer it up. Roughly, you want two or three parts browns to one part greens by volume:

• Greens: grass clippings, kitchen peelings, comfrey, spent annuals, poultry manure, nettles.
• Browns: torn cardboard, straw, shredded paper, woodchip, dead leaves, chopped stems.

Keep a bag of shredded cardboard or straw beside the bin and add a handful each time you tip in kitchen scraps. Chop anything woody with secateurs. Water the layers as you go in dry weather — the heap should feel like a wrung-out sponge, no wetter. Cover the top with old carpet or a flattened cardboard sheet to hold in heat and keep the rain out.

Turning, Monitoring and Harvesting

Turn the heap once a month with a fork, working from the outside in and the bottom to the top, moving it into the empty bay next door. This is what speeds everything up: it lets oxygen back in and evens out the moisture. A well-built heap hits 60°C within days. If yours does not heat at all, it is usually too dry, short of greens, or too small — remedy whichever applies and give it another fortnight.

After each turn the volume drops by about a third. Expect finished compost in three to six months over summer, longer over winter. When it is dark, crumbly, smells like woodland soil and you cannot recognise the original ingredients, it is ready. Sieve out the lumps, put them back to finish, and spread the rest on the beds, round the fruit bushes, or as a mulch in the kitchen garden.

A second bay means you are never short of somewhere to put the next barrowload. Two pallet bins, a bit of cardboard and ten minutes a month with a fork: that is the whole system.