A three-bin composting system is the workhorse of community gardens, school grounds and market farms. Three connected bays let you work in stages — one bin filling, one bin cooking, one bin finishing — so there is always compost ready to use. For anyone managing large volumes of garden waste, a three-bin system is the most practical, durable and satisfying way to compost.
This guide covers building the bays, running the three-stage rhythm, managing the pile, and using the finished compost — with adaptations for every budget and climate.
Why Three Bins?
A single pile forces a choice: stop adding fresh material and wait for it to finish, or keep adding and never get finished compost. Three bays solve that problem with a simple assembly line.
The Three Stages
- Bin 1 — Filling: fresh material is layered in every day until the bay is full.
- Bin 2 — Cooking: the full bay is turned into the middle bin, where the hot phase does its work.
- Bin 3 — Finishing: the turned pile rests and matures into dark, crumbly compost while a new batch starts in Bin 1.
"One bin is a pile. Three bins are a factory."
Building Your Bays
Bays can be built from almost anything durable: wooden pallets, planks, bricks, blocks, or wire mesh on timber frames. Each bay should hold about one cubic metre — large enough to heat, small enough to turn by hand.
Simple Pallet Bays
- Position: level ground, partial shade, near a water point and the garden.
- Frame: stand three pallets in a U shape and lash or screw them together; repeat twice beside the first bay to make three connected cells.
- Front: leave the fourth side open, or fit a removable board front held by wooden runners so material is easy to fork out.
- Roof: a simple cover of corrugated sheet or waterproof canvas keeps rain out while allowing air to flow.
Durable Block or Brick Bays
For permanent community sites, bays built from blocks or bricks with removable timber slats at the front will last for decades. Leave gaps between blocks for aeration, and set the base on compacted soil — never concrete — so worms and soil life can move up into the pile.