Wrigglers turn food waste into black gold for the garden, writes Meg Liptrot.

Worm bins and bokashi systems are fast becoming an expedient, clever way to deal with food waste, and they're great ways to keep your garden healthy and kids entertained.

As most of us know by now, food waste should never be put in the bin with general waste. It requires its own sorting bin, and to be handled completely separately from other types of waste. Many families, schools and businesses are thinking about how to turn their food waste into a resource instead.

Unfortunately, if food waste is thrown into general waste and ends up in landfill, the gas and leachate it produces cause serious pollution. The resulting methane gas is more damaging than carbon dioxide, and contributes to global warming and climate change.

Food waste is anything generated in the kitchen: vege peelings, leftover lunches and dinner scraps, eggshells, teabags and coffee grounds. Something to consider when throwing this waste out with the trash is that you are also throwing money down the drain.


It is easy to harvest that waste by turning it into compost and nutrient-rich fertiliser for a healthy, abundant garden. There's no need to buy fertiliser when you can make your own. A worm bin is also a fun way to involve kids in the garden, tending their own farm, complete with wriggly, intriguing "pets".

On properties where space is an issue, bokashi bins are good options. These were developed in Japan for apartment-dwellers, and are best used for cooked food, meat scraps and so on. The fermented waste can be dug into communal gardens, or given to friends who are generally very pleased to add the extra nutrients to their gardens. Cooked food waste can be processed by means of a bokashi system or two, but fresh kitchen scraps, coffee grounds and teabags can be put through a worm bin.

Essentially, a bokashi bin is a square, lidded bucket with drainage holes in the bottom, sitting inside another bucket. Apply a couple of tablespoons of bokashi "zing" to the top of your mix. The beneficial micro-organisms in the zing ferment your food. The zing is sawdust-like material loaded with beneficial fermentation enzymes and microbes and comes with your bucket when you buy it. One bag of zing will last two to four months; a replacement bag costs $9.

Bokashi is an anaerobic process that keeps air and light out. The final product smells pickled rather than like rotted food. The double-layered bins let liquid drain through, which should be removed regularly and diluted for use in the garden, or poured neat down the drain. The micro-organisms help balance problem drains and make them less stinky, similar to the way yoghurt introduces good bacteria to our digestive tracts.

Worm bins are an easy way to go if you have a bit of a backyard. They are usually three-tiered, and the vermicast (friable, odourless worm castings) need only be removed for use in the garden every several months or more, depending on the size of your system. An efficient worm bin doesn't stink, and can even sit near the back door in a spot out of full sun. The resulting "black gold", or vermicast, can be dug in to improve soil structure and health for great garden plants, and the liquid can be used diluted as foliar feed, poured on plants with a watering can, or into soil.

The worms used in worm bins are not natives, but exotic tiger worms that eat half their body weight in a day. They double their population every couple of months. About 500g of mature tiger worms will eat 225g of waste each day. The more worms, the faster you can add kitchen scraps. Worms regulate their population based on the size of bin. You can also add shredded, uncoated office paper, unscented toilet rolls, untreated sawdust, torn up egg cartons and so on as the carbon content to balance out the high nitrogen content of food scraps.

Worm bin dos and don'ts
* Worms do best at a temperature of between 10 and 30C. Too cold and they will become inactive, too much heat can kill them.

* A damp cloth sack over the scraps will keep the temperature and moisture levels even. The moisture level should be like a damp, squeezed out sponge.

* Bin smelling a bit strong? You probably have too much ammonia-producing nitrogenous food waste and need to balance your system with carbon sources. Try throwing in a handful of shredded paper or untreated sawdust when you throw in food scraps.

* Finding other insects living inside your bin? Don't worry, as they're helping the decomposition process. If you have vinegar flies, keep the surface of foodscraps covered with a damp sack, and add carbonous materials and a little lime. Add more water if you're getting slaters.

* A couple of litres of water added to the bin every 2-3 weeks will flush through for some nice vermi-liquid in your lowest tray, just turn the tap on for instant black gold.

* Worms won't be happy if you add lots of orange or grapefruit skin. Likewise, worms won't appreciate too much onion skin, cooking oils, bread, or cooked food. Use a bokashi bin instead.

* Bokashi: For cooked food waste and food not suitable for wormbins, or those with less space.

* Tiered worm bins: Worms-R-Us bin (square), Worm-A-Round, Can-O-Worms, Worm Cafe.

* Hungry bin: A system which does not involve lifting tiers and is mobile. It is a slightly funnel-shaped bin on wheels with a tray at the base for easy access to worm-castings.

* A range of operating bins can be viewed in action at the Sustainable Living Centre, New Lynn.

* Worm bins and worms are available to purchase at garden centres, some home supply depots, or direct from suppliers.