Building a Compost Bin from Pallets

Why Pallets Make Sense for Composting

A standard wooden pallet is roughly 1.2 metres by 1 metre, built from slats with gaps already in place. That spacing is exactly what a compost heap wants: enough airflow to keep the aerobic bacteria working, but not so much that the pile dries out and stalls. You are essentially getting a ready-made, pre-ventilated panel for free.

There is a satisfying symmetry to it, too. Pallets are themselves a waste product, often used once and then stacked behind a workshop or skipped. Turning three or four of them into a bin that transforms kitchen scraps and garden clippings into black gold is one of the neatest full circles in gardening. A three-bay pallet system can be built in an afternoon with basic tools, and it will last five to ten years if you treat it kindly.

Sourcing and Checking Your Pallets

Ask at builders' merchants, garden centres, bike shops and anywhere that receives deliveries on pallets. Most are only too pleased to see them go. Look for the stamped code on the corner block: HT means heat treated, which is fine. Avoid anything marked MB, which indicates methyl bromide fumigation, and steer clear of pallets that have carried chemicals, paint or produce that has obviously leaked.

Give each pallet a once-over before you commit. Reject any with split stringers, rot, or rusty nails protruding at odd angles. Blue and red painted pallets are usually owned by pooling schemes, so leave those where they are and take the plain wooden ones instead.

Once home, knock out any loose splinters, pull stray nails with a claw hammer or pry bar, and give the wood a quick brush down. There is no need to sand or treat it — untreated timber will weather to a silvery grey and rot down eventually, which is no bad thing.

What You Will Need

• Three or four pallets of similar size
• A hammer and a supply of 75mm galvanised nails, or a cordless drill with 100mm screws
• Heavy-duty wire cutters and a pry bar for removing nails
• Two or three metal corner brackets or lengths of sturdy batten for joining panels
• Gardening gloves and eye protection
• Optional: a length of old carpet or a tarpaulin for covering the heap

If you can find pallets with closely spaced slats, save those for the sides. Wider gaps are better suited to the base, where you want plenty of air and drainage.

Building the Bin, Step by Step

Choose a level spot on bare soil rather than paving. Worms and microbes need to travel up into the heap from below, and the soil will soak up any liquid that drains through. A site that gets a bit of sun is ideal, though partial shade is fine.

Stand one pallet on its edge to form the back. Take a second pallet and position it at right angles to form a side, then fix the two together along the corner using brackets or a batten screwed through both. Repeat with the third pallet for the opposite side, leaving the front open. If you have a fourth pallet, hinge it on with two screws at the top corner so it swings open — a lift-off front panel is even simpler, held in place by two short lengths of timber nailed to the side panels as guides.

Line the base with a few sheets of cardboard, overlapping the edges, and soak them. This suppresses weeds underneath and gives the heap a carbon-rich first layer. A single bay of roughly one cubic metre is plenty for a typical household. If you have the space and the appetite, build two bays side by side: one for filling, one for turning and maturing.

Filling It Properly

The old rule of thumb is roughly two parts brown to one part green by volume. Browns are your carbon: cardboard, shredded paper, dead leaves, straw, twiggy prunings. Greens are your nitrogen: grass clippings, vegetable peelings, coffee grounds, annual weeds before they set seed. Alternate thin layers rather than dumping everything in at once, and aim for pieces no bigger than your thumb.

Keep a small lidded caddy in the kitchen and add a handful of shredded cardboard each time you empty it. Turn the heap every fortnight or so with a fork, moving the outside to the middle and the middle to the outside. Water it if it looks dry; cover it with a bit of old carpet if it is sodden after heavy rain.

Keeping It Working

In a warm spell a well-built heap will reach 60°C or more in the centre, and you will see it shrink noticeably within a week. That heat is the sign that everything is ticking over nicely. If the pile feels cold and slimy, you have too much green material and not enough air — turn it and add cardboard. If it is dry and nothing seems to be happening, water it and add grass clippings.

Expect usable compost in three to six months in summer, longer over winter, when the process slows to a crawl. When the material is dark, crumbly and smells of woodland floor, it is ready. Screen out any stubborn twigs and return them to the next heap. Your reward is a barrowload of free compost and one less pile of pallets going to waste.