How do I start composting?

Composting is a controlled decomposition, and the organisms doing it need four things: carbon, nitrogen, air and moisture. Nearly every problem — slime, smell, or a heap that just sits there — is one of those four being wrong, and usually it's too much nitrogen and not enough air.

What you'll need

• Compost bin or a space for an open heap
• Garden fork for turning
• A source of browns — cardboard, dry leaves, shredded paper
• Bucket for kitchen scraps (optional)

Step by step

1. Site the bin on soil rather than a hard surface, somewhere reasonably accessible.Contact with soil lets worms and organisms move in. Accessibility decides whether you actually use it.
2. Start with a layer of coarse material — twigs or woody prunings — at the base.It lets air in from below, which most heaps lack.
3. Add roughly equal volumes of greens and browns as you go.Greens: vegetable peelings, grass, coffee grounds, tea leaves. Browns: cardboard, dry leaves, paper, straw, small woody prunings.
4. Tear cardboard into pieces rather than adding whole flattened boxes.Whole sheets form impermeable layers that block air and water.
5. Keep it as damp as a wrung-out sponge.Too dry and nothing happens; too wet and it goes anaerobic and smells. Cover an open heap in heavy rain.
6. Turn it every few weeks with a fork if you want it fast.Turning adds air, which is the main accelerator. An unturned heap still works — it just takes a year or more.
7. Don't add cooked food, meat, fish or dairy to an open heap.They attract rats and smell. A closed hot bin or a bokashi system can handle them; an open heap can't.
8. Use it when it's dark, crumbly and smells of earth — 6–12 months typically.It doesn't need to be perfectly uniform. Sieve out the big bits and put them back in the heap.

Tips

• Keep a bag or bin of torn cardboard next to the compost bin. The main reason heaps go wrong is that greens arrive daily and browns don't.
• Grass clippings alone will turn into a slimy anaerobic mat. Always mix them with plenty of browns.
• Two bins are much better than one: fill the first while the second matures.
• If it smells of ammonia, it needs browns and air. If it's dry and unchanged, it needs water and greens.

Common mistakes

• Too many greens — The commonest failure — slimy, smelly and anaerobic. Add cardboard and turn it.
• Adding whole flattened cardboard boxes — They mat into airtight layers. Tear them up first.
• Adding cooked food to an open heap — Attracts rats and produces smells the heap can't process.
• Never turning it and expecting fast results — It'll still compost, but over a year or more rather than months.

Questions people ask