Everyone knows they ought to compost, yet half the bins in the country sit as a cold, slimy, smelly mass that never turns into anything useful. Getting it right is not hard once you understand the one thing that makes it work.
Greens and browns
The secret is balance. A good heap needs roughly equal parts of soft green material, which is rich in nitrogen, and dry brown material, which provides carbon. Too much green and it goes slimy; too much brown and nothing happens at all.
- Greens: grass clippings, vegetable peelings, soft prunings, coffee grounds.
- Browns: cardboard, dead leaves, straw, woody stems, paper.
- Leave out: cooked food, meat and perennial weed roots.
Air and moisture
The bacteria doing the work need air, so a heap that is just grass packs down airless and sour. Mixing in plenty of scrunched cardboard keeps it open. It should feel about as damp as a wrung-out sponge, no wetter.
Turn it now and then
Forking the heap over every few weeks introduces air and speeds everything up no end, mixing the cooler edges into the warm middle. A heap left untouched will compost eventually, just far more slowly and less evenly.
Knowing when it is ready
Finished compost is dark, crumbly and smells of woodland floor, with the original ingredients no longer recognisable. It can take six months to a year. Spread it on the beds as a mulch, and the garden hands your kitchen waste straight back as free fertility.