Building a Compost Bin

Why Build Rather Than Buy?

Purpose-built compost bins from timber are larger, better-ventilated, and more effective than most plastic "dalek" bins available from garden centres. A wooden bay allows proper airflow, is easy to fill and turn, can be built to any size, and costs very little to construct — scaffolding boards, old pallets, or rough-sawn timber all work well.

The Minimum: A Single Bay

A single compost bay of 1m × 1m × 1m (1 cubic metre) is the minimum useful size. Smaller heaps do not retain heat efficiently and decompose slowly. The bay can be three-sided with the fourth side open for access, or made with removable front boards that can be slid out when the heap is ready to turn or use.

The Better System: Three Bays

Experienced composters use a three-bay system:

Bay 1: The active bay. Fresh material goes here as it is produced. Add greens and browns in layers, keep moist, keep covered.

Bay 2: The turning bay. When Bay 1 is full, the contents are turned into Bay 2. This aerates the heap, triggers a second heating phase, and brings the outer material to the centre. Bay 1 is now free to receive new material.

Bay 3: The maturing bay. Once Bay 2 has broken down, the partially composted material moves to Bay 3 to finish. Finished compost (dark, crumbly, smelling of earth) is used from here.

The system maintains a continuous supply of compost at different stages of readiness.

Construction

The simplest three-bay system is made from scaffolding boards or rough-sawn timber:

1. Set four vertical posts (75mm × 75mm) for each bay, 1m apart front to back and 1m between bays.
2. Nail boards horizontally to the back and sides, leaving small gaps (1–2cm) between boards for airflow.
3. Leave the front open, or use removable boards slotted into vertical runners.
4. Treat timber with raw linseed oil if you want to extend its life — avoid chemical preservatives near soil and food crops.

Location

Site the compost area in partial shade (full sun dries it out quickly) with easy access from the kitchen garden paths. It should be close enough to the garden to make regular additions convenient, but not so prominent as to be an eyesore.

Accelerating Decomposition

• Chop or shred material before adding — smaller pieces break down faster
• Mix greens and browns as you add them; avoid adding large quantities of one material alone
• Keep the heap damp (like a wrung-out sponge, not wet)
• Turn every 4–6 weeks
• Add a thin layer of finished compost or soil between layers to inoculate with micro-organisms