Build a simple compost bin from recycled wood

Why a slatted bay beats a plastic bin

A simple wooden bay is the most forgiving compost bin you can own. The gaps between the slats let air move freely through the heap, and air is what separates sweet, crumbly compost from a slimy, sour mess. Sealed plastic cones and tumblers tend to turn anaerobic, particularly through a wet British winter, whereas a slatted bay breathes on its own. It also holds a proper volume — around a cubic metre — which means the heap can actually heat up in the middle and get the composting process motoring.

Best of all, it costs very little if you build it from reclaimed timber. Set aside a morning, a few hand tools and roughly eight to ten metres of usable wood, and you will have a bin that keeps working for a decade.

Choosing the right spot

Siting matters more than most people expect. Compost needs soil contact, so stand the bay on bare earth rather than paving or decking — worms and soil microbes will move up into the heap and do half the work for you.

• Part shade is ideal. Full sun dries a heap out; deep shade keeps it cold and soggy.
• Not against a fence you share with neighbours, and not tight against the house. Rodents are far less likely to take an interest if the bin is out in the open, well away from walls and sheds.
• Room for a second bay alongside it. Two bays side by side make turning infinitely easier — you simply fork the contents from one into the other.
• A level base. Clear the ground of perennial weeds and level it with a rake or a bit of sand before you start.

Sourcing and preparing the wood

Pallets, old fence panels, scaffold boards and decking offcuts all work well. Look for timber around 20–25mm thick — thin enough to be light, thick enough to hold a screw without splitting. Untreated softwood is fine; it will start to rot after eight or ten years, which is roughly how long a heap takes to fill and empty a few times anyway.

Do avoid anything with old creosote, lead-based paint or heavy chemical staining. These can leach into your compost, and there is no sense taking the risk when clean reclaimed wood is easy to find.

Pull out every nail and staple before you saw. Stack your cut pieces by length so you are not hunting for a short slat halfway through the build.

Building the bay, step by step

Aim for an internal size of roughly one metre wide, one metre deep and one metre high. That volume holds enough material to generate heat, but stays small enough to reach into with a fork.

• Posts: cut four lengths of 75 x 75mm timber to 1.2 metres. Sink each one about 250mm into the ground, or sit them on concrete blocks if you would rather not dig.
• Slats: cut your boards to roughly 1.1 metres and screw them horizontally to the three fixed sides, leaving a 20–25mm gap between each. Use two screws per slat per post for rigidity.
• The open side: leave the front unfixed, or make it with slats that slot into simple brackets and lift out. You will want easy access when you turn the heap.
• The lid: a loose board or a piece of old tarpaulin weighted with a brick keeps rain from saturating the heap while still allowing air in.

Filling it: greens and browns

The trick to good compost is balance. Aim for roughly equal volumes of greens (wet, nitrogen-rich material) and browns (dry, carbon-rich material), and add them in thin layers rather than dumping a whole bucket of one thing at a time.

• Greens: vegetable peelings, tea bags, coffee grounds, grass clippings, annual weeds, spent flowers and soft prunings.
• Browns: shredded cardboard, newspaper, egg boxes, straw, dry leaves, woodchip and the contents of your paper shredder.
• Leave out: meat, fish, dairy and cooked food, which attract rats; perennial weeds such as bindweed and ground elder; diseased plant material; and dog or cat waste.

If the heap starts to smell sour or looks slimy, you need more browns. If it seems dry and nothing is happening, add greens and a splash of water.

Turning, moisture and when it is ready

Turn the heap with a fork every two to four weeks. Move the outside material into the middle and the middle to the outside — that is where the heat and the fastest decomposition happen. Turning is also the moment to check moisture: squeeze a handful of the contents. It should feel like a wrung-out sponge. Drier than that, water it as you rebuild the heap; wetter, fork in more shredded cardboard.

A well-managed heap will reach 55–65°C in the centre within a few days of a good turn. You can feel the warmth with your hand, and steam may rise off it on a cold morning. That heat kills many weed seeds and pathogens, which is another good reason to keep the bin large enough to work properly.

Compost is ready when it is dark, crumbly and smells of woodland floor after rain — no recognisable scraps, no eggshell labels, no banana skins. Turned regularly, that takes three to six months; left alone, closer to a year. Sieve out anything woody and throw it into the next heap to start again. Then spread the finished stuff on your beds, mulch your borders, and start the whole cycle over.