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Composting

How to Make a Compost Bin: Three Designs That Work

A heap needs about a cubic yard to heat up, air to keep going, and a lid in wet climates. Pallet, wire and bin designs, plus what actually goes in.

By The Grow In Backyard Team 4 min read Save to Pinterest — opens Pinterest in a new tab
A row of open-fronted timber compost bins in a garden
Photo: Acabashi, CC BY-SA 4.0, via Wikimedia Commons
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A compost bin has three jobs: hold the material in a heap big enough to heat, let air through, and keep the worst of the rain off. Everything beyond that is convenience.

The single most important number is volume. Below roughly a cubic yard, a heap cannot hold the heat its own microbes generate, and it never gets hot.

Three designs

Compost bin designs compared
DesignCostBuild timeLifeBest for
Four pallets, wiredOften free20 min3–5 yrsMost gardens; the default
Wire mesh cylinderVery low15 min5+ yrsLeaves, easy access, small spaces
Timber slatted baysMediumA day10+ yrsPermanent multi-bay setups
Plastic dalek binLow–mediumNone10+ yrsSmall gardens, kitchen waste, rat resistance
TumblerMedium–highNone5–10 yrsFast small batches; limited volume
Open heap, no binFreeNone—Large gardens with space to spare

Pallet bin. Four pallets on edge in a square, corners fixed with brackets or wire, front slotted or hinged so it lifts away. Twenty minutes, usually free. Line the inside with cardboard if the slats are too open.

Wire mesh cylinder. A length of galvanised mesh formed into a circle and tied. Excellent for leaves specifically, and the whole cylinder lifts off, leaving the heap standing — which makes turning trivial.

Slatted timber bays. The permanent option: three bays in a row for filling, turning and finished compost, with removable front boards. Worth building if composting is a long-term habit.

Two bins solve the main frustration

With one bin, fresh scraps keep landing on compost that is nearly finished, and nothing is ever ready. Two bins let one fill while the other matures. Three — filling, turning, finished — is the traditional arrangement and is genuinely better than two if you have the room.

Siting

  • On soil, not paving. Worms, beetles and soil microbes migrate up into the heap, and excess water drains away.
  • Partial shade. Full sun dries it out; deep shade keeps it cold.
  • Level, and reachable with a wheelbarrow.
  • Not right against a fence or wall — leave room to work around it.

What goes in

Browns and greens
Browns (carbon)Greens (nitrogen)
Dry leavesGrass clippings
Cardboard, torn upKitchen fruit and vegetable scraps
StrawFresh weeds, before they seed
Woody prunings, shreddedCoffee grounds and tea leaves
Paper, shreddedManure from herbivores
Sawdust from untreated woodSoft green prunings
Egg boxes, toilet roll tubesSpent plants at the end of a season

Roughly two parts browns to one part greens by volume. Precision is not needed — the heap tells you when it is wrong. Slimy and smelly means too much green; dry and inert means too much brown.

Keep out:

  • Meat, fish, dairy, cooked food — rats and smell.
  • Dog and cat faeces — pathogens.
  • Diseased plant material — a domestic heap rarely gets hot enough to be reliable, which is why blighted tomato foliage goes in the bin.
  • Perennial weed roots — bindweed, couch grass, ground elder. They survive and spread.
  • Anything treated with persistent herbicide. Aminopyralid and similar compounds survive composting and the digestive tract of animals, and they damage plants for years. Be careful with imported manure and grass clippings of unknown origin.
  • Glossy printed card, coal ash, treated timber.

Getting it hot, or not bothering

Hot composting — turning every few days, balanced inputs, enough volume — reaches 130–160°F, kills most weed seed and pathogens, and finishes in two to three months. It is real work.

Cold composting — pile it up and wait — takes about a year and needs almost nothing. The compost is just as good. Weed seeds survive, so keep seeding weeds out.

Most gardens do a version somewhere between the two, and that is fine.

Troubleshooting

Smells sour or of ammonia — anaerobic. Turn it, add dry browns, cover it if it is rain-soaked.

Nothing happening — too dry, too small, or too brown. Water it, add greens, and consider whether the heap is big enough.

Flies — bury kitchen scraps under a layer of browns rather than leaving them on top.

Rats — usually cooked food or meat going in. Remove the source; a solid-based bin with a lid helps in persistent cases.

Ants — the heap is too dry. Water it and turn it.

Knowing when it is done

Dark brown, crumbly, smelling of woodland soil, with nothing recognisable in it except the odd twig. It should have roughly halved in volume.

Sieve it if you want a fine product, and throw whatever is left in the sieve back into the next heap as a starter — it is full of the organisms you want.

Step by step

Time
PT2H
Cost
$30
You need
Four wooden pallets, or wire mesh, or a plastic bin, Fixings — brackets, wire, or screws, Cardboard or a lid
Tools
Drill and driver, Wire cutters or a saw, Garden fork

  1. Size it to about a cubic yard

    Three feet by three feet by three feet is the standard minimum for a heap that heats up, because a smaller volume loses heat faster than the microbes generate it. Smaller bins still make compost, just slowly and without reaching temperatures that kill weed seed.

  2. Pick a level, well-drained spot on soil

    Site the bin directly on soil rather than on paving, so worms and soil organisms can move in and excess water can drain away. Partial shade is ideal — full sun dries the heap out, deep shade keeps it cold and slow.

  3. Build the frame, leaving gaps for air

    Stand four pallets on edge in a square and fix the corners with brackets or wire, leaving the front removable. Or form a cylinder from wire mesh and tie the seam. Air is what keeps decomposition aerobic, and a sealed container turns anaerobic and smells.

  4. Leave the front openable

    Fix three sides permanently and hinge or slot the fourth, so you can fork the heap out. A bin you cannot easily empty is the main reason people abandon composting after a year.

  5. Layer browns and greens roughly two to one

    Alternate carbon-rich browns — dry leaves, cardboard, straw, woody prunings — with nitrogen-rich greens such as grass clippings, kitchen scraps and fresh weeds. Roughly two parts browns to one part greens by volume works in practice.

  6. Keep it as damp as a wrung-out sponge

    Too dry and decomposition stalls; too wet and it goes anaerobic and sour. Add a lid or a sheet of cardboard in wet climates, and water the heap in dry spells.

  7. Turn it every few weeks if you want it fast

    Turning reintroduces air and moves the cooler outside material into the hot centre. A turned heap can finish in two to three months; an unturned one takes a year but needs almost no work.

  8. Use it when it is dark, crumbly and smells of earth

    Finished compost is dark brown, crumbly, and smells of woodland soil with no recognisable ingredients apart from the odd twig. Sieve out anything coarse and put it back into the next heap.

Common questions

How big does a compost bin need to be?

About a cubic yard — three feet in each direction — is the minimum for a heap that heats up properly, because a smaller mass loses heat faster than the microbes can generate it. Smaller bins still produce compost through slower cold decomposition, but they will not reach the 130 to 160°F that kills weed seed and pathogens.

What is the cheapest way to build a compost bin?

Four wooden pallets stood on edge and wired at the corners, which is often free and takes twenty minutes. A cylinder of wire mesh is nearly as cheap and easier to lift off the heap. Both give the air circulation that matters far more than appearance.

What should not go in a compost bin?

Meat, fish, dairy and cooked food, which attract rats and smell; dog and cat faeces; diseased plant material; perennial weed roots such as bindweed and couch grass; and anything treated with persistent herbicide, which survives composting and damages plants afterwards. Glossy printed card and coal ash are also best left out.

Why does my compost smell bad?

It has gone anaerobic — too wet, too compacted, or too much green material. A healthy heap smells earthy. A sour or ammonia smell means it needs air and carbon: turn it, and mix in dry browns such as shredded cardboard, straw or autumn leaves. Adding a lid in a wet climate prevents the problem recurring.

How long does compost take?

Two to three months for a turned, well-balanced heap that heats up, and around a year for one left alone. Both produce good compost. The choice is between effort and time — an unturned heap in a corner needs almost nothing from you, and simply takes longer.

Do you need two compost bins?

It helps considerably. One bin fills while the other finishes, so you always have somewhere to put fresh material and somewhere maturing. Three is the traditional arrangement — filling, turning, finished — and if you have the space it removes the main frustration of single-bin composting.

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