Why pallets make a sturdy, cheap bin

A compost bin only needs to do three things: hold a decent volume of material, let air in at the sides, and sit on bare soil so worms and fungi can move in. Four wooden pallets do all of that for the price of a few nails. Most pallets measure around 1.2 by 1 metre, so a bin made from four of them gives you roughly a cubic metre of space — about the smallest volume that will heat up properly and rot down in a reasonable time.

Check the stamp before you take a pallet home. You want ones marked HT, meaning heat-treated. Avoid anything marked MB, which has been fumigated, along with pallets that are stained, painted or have carried chemicals. Plain softwood pallets that have stood outside in the rain for a few months are ideal.

Siting the bin

Put it on bare soil or turf, never on concrete or paving. Contact with the ground is what lets soil life colonise the heap, and it stops the base turning into a stagnant slurry. Beyond that:

• Level ground, so the pallets sit flat and don't twist as they settle.
• Part shade. Some sun helps the heap warm up; all-day baking dries it out.
• Room to work. Leave a metre in front of the side you'll open — you'll be there with a fork far more often than you expect.
• Near a tap or water butt, because dry heaps stall in summer.
• Away from fences and the house. A permanently damp bin will rot a fence panel in a couple of seasons.

Building it in an afternoon

You need four pallets, galvanised nails or coach bolts, four sturdy stakes, and some wire or cable ties.

• Stand three pallets on edge in a U-shape, slats facing inwards so material doesn't fall through the gaps. Fix them to each other with nails, or lash each corner to a stake driven into the ground.
• Leave the fourth as a removable front panel. Hook it onto the corner stakes with wire loops so you can lift it off to turn or empty the heap.
• Line the slatted sides with damp cardboard if the gaps are wide. It keeps material in, holds moisture, and rots down into the mix itself.
• No base is needed. A sheet of old carpet over the top in winter stops the rain waterlogging it.

The green and brown balance

This is where most heaps succeed or fail. Greens are the wet, nitrogen-rich material that gets things going; browns are dry and carbon-rich, and give the heap structure and air. Aim for roughly two parts browns to one part greens by volume, and keep a bag of torn cardboard beside the bin so you can add a handful whenever you tip in kitchen waste.

• Greens: grass clippings, vegetable peelings, coffee grounds, annual weeds before they set seed, nettles, spent bedding plants.
• Browns: torn cardboard and egg boxes, newspaper, straw, dry leaves, woodchip, twiggy prunings.
• Leave out: meat, dairy, cooked food in an open heap, diseased plants, and perennial roots such as bindweed and ground elder.

Add in thin layers rather than emptying a whole bucket of grass in one go — a thick mat of clippings turns to slime and blocks air.

Turning, moisture and common problems

Aim for a heap that feels like a wrung-out sponge. Squeeze a handful: if water drips out it's too wet, and if it's dusty it needs watering. Turn the heap every two to four weeks with a fork, pulling material from the outside into the middle. This is the single biggest difference between compost in six months and compost in two years.

• Sour, eggy smell: too wet and short of air. Turn it and mix in a bucketful of torn cardboard.
• Nothing happening: too dry, or too small a volume. Water it, add material, and build up a full cubic metre before expecting heat.
• Rats or flies: usually buried kitchen waste. Dig it into the middle and cover with browns.

When it's ready

Six to twelve months on, the bottom of the heap will be dark, crumbly and smell of woodland floor rather than rot. That's compost. Lift off the front panel, fork out the finished material, and return anything still recognisable to the heap to finish off.

Sieve it over a wheelbarrow if you like: the coarse bits make a fine mulch around shrubs, while the fine stuff is perfect for dressing vegetable beds or mixing into potting compost at about one part compost to two parts bought mix. Once you've spread the first barrowload, you'll start eyeing up every pallet you pass.