Worm Farming in New Zealand

A worm farm turns your kitchen scraps into some of the best plant food you can get, and it fits almost anywhere. You do not need a garden to run one. A worm farm happily lives in a carport, shed, garage or shady corner of a courtyard, which makes it ideal for renters and small sections.

New Zealand's temperate climate suits composting worms well. The work is mostly feeding them and keeping conditions right, and in return you get vermicast and a nutrient rich liquid to feed the garden. This hub covers setting up, what to feed, and how to harvest the castings.

Setting up a worm farm

The composting worm used in New Zealand is the tiger worm, not the earthworm you dig up in the lawn. Tiger worms are surface feeders that thrive in a moist, dark bin of organic matter. They do best between about 15 and 25 degrees, so a cool, shady, sheltered spot is what you are after.

Start the bin with damp bedding such as shredded cardboard, newspaper or coconut fibre, then add your worms and let them settle before you feed heavily. In colder regions, insulate the bin over winter with a hessian sack or a straw bale so the worms keep ticking over.

You can buy a tiered plastic worm farm or build your own from stacked bins or an old bath. The principle is the same: worms work upward toward fresh food, leaving finished castings below.

• A worm bin in a cool, shady, sheltered spot
• Tiger worms (Eisenia fetida) to start the colony
• Damp bedding such as shredded cardboard, paper or coconut fibre
• A cover or lid to keep it dark and moist

What to feed and what to avoid

Worms eat most of your raw kitchen waste, and the smaller you chop it the faster they get through it. Feed in moderation and wait until the last lot is being worked through before adding more, so the bin does not turn sour.

Some things upset a worm farm and are best kept out. Worms struggle with citrus, onion and other strong scraps, and oily or dairy foods cause problems. Keep those for the bokashi bin or hot compost instead.

• Good: fruit and vegetable scraps, coffee grounds, tea, crushed eggshell, small amounts of paper and cardboard
• Avoid: citrus, kiwifruit, onion skins, oil, dairy, and large amounts of cooked or salty food
• Chop scraps small so the worms process them faster
• Feed little and often rather than dumping a big load at once

Harvesting castings and worm tea

The finished product is vermicast, dark crumbly worm castings that are a powerful soil conditioner and far richer than ordinary soil. Dig a handful through planting holes, top dress pots, or brew it into the garden.

A tiered farm makes harvesting easy. Stop feeding the lower tray, let the worms migrate up to the fresh food above, then lift off the bottom tray of finished castings. Most farms also collect a liquid at the base, which you dilute to the colour of weak tea before watering it onto plants.