Autumn is when a garden makes the most waste in the shortest time: spent crops, dead-headings, the first fallen leaves. That is usually when a single compost heap stops keeping up, because there is nowhere to put new waste without disturbing what is already rotting down. A two-bay bin solves this with one side filling while the other is left alone to finish. Built from timber posts and weld mesh, it needs no concrete and can be put up in an afternoon.

Build a Two-Bay Timber and Wire Compost Bin

What you need

6 treated timber posts, 75mm x 75mm x 1.2m one per corner, two shared for the middle divider
6 metal post spikes to fit the posts drive-in supports, no concrete needed on firm ground
6 m galvanised weld mesh, 900mm high covers the back and both sides of the two bays
1 box fencing staples
6 scaffold boards or timber slats, 1m long three per bay, for a removable front
1 box 50mm exterior screws for the guide battens that hold the slats
4 timber battens, 25mm x 25mm x 1m screwed to front posts as slat guides

Step by step

Mark out two 1m squares side by side and drive a post spike at each of the six corner and divider positions, checking each is vertical with a spirit level as you go.
60 min
Drop a timber post into each spike and tighten the grub screws, sighting along the row to keep the tops level.
20 min
Screw a pair of guide battens to the inside faces of each front post, spaced apart by the thickness of a scaffold board, to hold the removable front slats.
30 min
Unroll the weld mesh along the back and sides of both bays, pulling it taut by hand, and staple it to the posts roughly every 150mm.
40 min
Cut the mesh where it meets a post or corner, and bend any sharp cut ends back on themselves so nothing is left exposed.
15 min
Slide the scaffold board slats down the front guide battens to close each bay, leaving them loose enough to lift out for turning or emptying.
15 min

Afterwards

Check the mesh staples and post spikes after the first hard frost or heavy wind, since ground movement can work them loose over winter. Lift the front slats out to turn the contents every few weeks, and mix in dry material such as cardboard or straw if it starts to smell or slump, which usually means too much wet green waste and not enough air.

Questions

Do the posts need concreting in?

Not on reasonably firm ground, where post spikes hold well. On soft or stony ground, concrete the posts in instead for stability.

Why weld mesh instead of solid boards on the sides?

Airflow through the mesh keeps the heap aerobic, which is what stops it turning slimy and smelling instead of rotting down cleanly.

How long before the first bay is ready to use?

A heap with a reasonable mix of green and brown waste, turned occasionally, is usually ready in six to twelve months. Let the second bay fill while the first finishes.

Can I use reclaimed pallets instead of buying timber?

Yes, if you can find pallets stamped HT for heat-treated rather than MB for chemically fumigated, and check they are square before building around them.