Composting in New Zealand

Compost is the engine room of a good garden. Every banana skin, handful of lawn clippings and spent pea vine can come back to you as dark, crumbly soil food. It costs nothing and it keeps a surprising amount of waste out of the bin.

Making compost in New Zealand is straightforward once you understand the balance the pile needs. Get the mix of wet and dry material right, keep a bit of air moving through it, and nature does most of the work for you.

Greens and browns: the basic balance

A good compost heap is a mix of two things. Greens are wet, soft and high in nitrogen. Browns are dry, woody and high in carbon. Roughly equal amounts by volume gives you a heap that breaks down fast and does not smell.

If your heap is slimy and stinks, it has too much green. Add browns and turn it. If it sits there dry and nothing happens, it has too much brown and not enough moisture. Add greens and a watering can.

• Greens: vegetable scraps, lawn clippings, coffee grounds, soft weeds, fruit peelings
• Browns: dry leaves, shredded cardboard, untreated sawdust, straw, pea straw, paper
• Add a few handfuls of garden soil or finished compost to bring in the microbes that do the work

What to keep out

Most kitchen and garden waste is fair game, but a few things cause trouble. Meat, fish, dairy and cooked food attract rats and flies, so leave those for a closed bokashi system or a council food scraps bin if your area has one.

Diseased plants, seeding weeds and any lawn clippings treated with weedkiller are also best left out. A home heap rarely gets hot enough to kill weed seeds or persistent sprays.

• Leave out: meat, fish, dairy, oils, cooked food, dog and cat waste
• Leave out: seeding weeds like onion weed and oxalis, and diseased plant material
• Leave out: anything sprayed with weedkiller or treated timber sawdust

Building and turning the heap

Layer your greens and browns like a lasagne as you go, and keep the heap about as moist as a wrung-out sponge. A bin or bay around a cubic metre is the sweet spot. Much smaller and it struggles to build heat.

Turn the pile every couple of weeks to get air in. This speeds things up and stops it going sour. In the warm north a heap can be ready in two to three months. In the cooler South Island it slows right down over winter and picks up again in spring.

Using your council green waste service

Councils across the country handle garden and food waste differently, so it pays to check your own. Some run a kerbside food scraps collection, some take garden waste in a green bin, and others, including Auckland, do not collect green waste at all.

What the green bin accepts also varies. Many councils refuse flax, cabbage tree leaves, bamboo and palm fronds because they are slow to break down. Composting the soft stuff at home and sending only the tough, woody material to the council is the tidiest approach.