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How to make compost at home

Composting is feeding living things. Bacteria, fungi, worms and beetles eat plant scraps and leave dark, crumbly compost that smells of a forest floor. Give them the right food, water and air, and compost makes itself.

The recipe

Use two to three buckets of browns for every bucket of greens. Keep the heap damp like a wrung-out sponge, and keep air in it.

Greens and browns

Greens are fresh and moist. They supply nitrogen:

• vegetable and fruit peels;
• tea leaves and coffee grounds;
• fresh grass clippings and weeds without seeds;
• fresh manure from cows, horses, goats, rabbits or chickens.

Browns are dry. They supply carbon:

• dry leaves, straw and dry grass;
• shredded cardboard, egg boxes and newspaper;
• untreated wood shavings and sawdust;
• dry maize stalks.

Too many greens and the heap turns wet, slimy and smelly. Add browns. Too many browns and the heap stays dry and does nothing. Add greens and water.

Most town households have plenty of greens. It is the browns that you must plan for. Store dry leaves in bags in autumn, and ask shops for clean cardboard.

Chop it up

Smaller is faster. A whole cabbage stalk or a sheet of cardboard takes months to break down. Chopped or torn, it takes weeks.

Water

Squeeze a handful from the middle of the heap.

• A few drops come out: about right.
• Water streams out: too wet. Add browns and turn the heap.
• Dry and crumbly: too dry. Water it as you turn it.

In dry parts of South Africa a heap can dry out in a week of summer heat, and in a Western Cape winter an open heap can become soaked. A cover of old carpet or sacks helps with both.

Air

Without air, the heap becomes slimy and smells of rotten eggs.

• Mix in coarse browns such as straw, shredded cardboard and twigs.
• Do not pack the heap down.
• Turn it now and then, or push a fork in to open air holes.

What not to compost at home

• human waste, nappies, and cat or dog waste;
• meat, fish, bones, dairy, fat and cooking oil, which smell and attract rats and flies;
• diseased plants, and weeds with seeds or running roots such as kweek;
• coal ash, and ash from treated or painted wood;
• glossy paper, plastic, glass, metal and "compostable" plastics;
• sawdust from treated timber, and anything sprayed with weedkiller.

In the kitchen

Keep a small tub with a lid on the counter. Empty it onto the heap every day or two and rinse it. A little shredded paper in the bottom soaks up juice and stops smells.

How long does it take?

Anything from six weeks to a year. A heap of about 1 m × 1 m × 1 m holds its heat, while a small pile stays cool and slow. A hot heap that is turned can be ready in 6 to 12 weeks. A cold heap left alone takes 6 to 12 months. Everything is faster in summer.

Compost is ready when it is dark and crumbly, smells earthy, and you can no longer recognise what went in. If it is still warm or smells sour, give it longer.

This guide is based on Chapter 3 of Composting, Worm Farming and Healthy Soil in South Africa, which goes on to bins, hot composting and bokashi.