Worm Farm NZ: How to Set Up, Feed and Harvest a Worm Farm

Updated October 2026

A worm farm is the easiest way to turn kitchen scraps into garden gold, even if you have no garden at all. It fits on a balcony, under the deck or in the shade beside the back door, and it works year round.

The worms do the eating, you do the feeding, and in return you get rich castings and a liquid feed called worm tea. Both are excellent for the garden and far gentler than any bagged fertiliser.

Choosing and setting up your farm

A stacked tray-style worm farm is the standard choice and you will find them in most garden centres. The worms work their way up through the trays as they finish each layer, which makes harvesting the castings simple.

Use tiger worms or red worms, sold by the thousand specifically for worm farming. Garden earthworms will not do the job. Start them on damp shredded paper or coconut fibre as bedding, then begin feeding lightly once they have settled.

How many worms to start with

The composting worms used in New Zealand are tiger worms (Eisenia fetida) and red wrigglers, surface feeders that live in the top layer of rotting matter and breed fast. About a thousand worms is a good start for a home farm, and they build up to fill it within a few months. Garden centres, worm farm suppliers and many council waste programmes sell them. Let the worms settle in their damp bedding for a few days before you feed heavily, then build the feeding up as the population grows.

What to feed your worms

Worms eat most of the same scraps you would compost, but they prefer it soft and chopped small. Feed little and often, and wait until they have worked through one feed before adding the next. Overfeeding is the most common beginner mistake.

Bury each feed under the bedding to keep flies and smells down, and tuck a sheet of damp newspaper or hessian over the top to keep things dark and moist.

• Feed: vegetable and fruit scraps, coffee grounds, tea leaves, crushed eggshells, soft garden waste
• Feed: shredded paper and cardboard in small amounts
• Avoid: meat, fish, dairy and oily food, and large amounts of citrus, onion or garlic
• Small amounts only: bread and plain cooked food

Worm Farming Through the Year in Your Region

Composting worms do best between about 15 and 25 degrees, so the job through the year is keeping the farm cool in summer and buffered from frost in winter. This table gives the average frost window for each of our nine New Zealand regions from our frost dates page.

Overheating in the sun is the quickest way to kill a worm farm in New Zealand, and it can happen in any region, so a spot under a deck, against a south wall or in a shed is the safe choice everywhere. In the frosty regions, from Waikato and the Bay of Plenty south, the same sheltered spot buffers the bin from frost, and a hessian sack or straw bale over it in winter keeps the worms working.

Keeping the farm healthy

Worms are happiest in the shade and out of temperature extremes. Keep the farm out of direct summer sun, which can cook them, and tuck it somewhere sheltered over a cold snap. Coastal wind also dries a farm out, so a sheltered corner helps.

If the farm turns smelly or acidic, ease off the feeding and add a sprinkle of garden lime or crushed eggshell to sweeten it. A handful of dry shredded paper helps soak up excess moisture.

Harvesting castings and worm tea

Worm tea drains from the bottom tap. Dilute it until it looks like weak tea, then water it onto your plants and soil. It is mild enough to use often through the growing season.

The dark crumbly castings are pure plant food. Scoop them from the lowest finished tray and dig a handful through the soil around hungry plants, or mix them into seed-raising and potting mixes for a gentle boost.

Common Worm Farm Problems

• Fruit flies: bury fresh food under the bedding and stop overfeeding.
• Ants: the bin is usually too dry, so dampen it and stand the legs in water.
• A soggy bin: mix in dry shredded paper or cardboard and check the drainage tap is clear, because worms drown in a waterlogged farm.
• Rats: keep meat, dairy and fat out entirely and secure the lid.

Our worm farm troubleshooting page covers each problem in more detail.

Worm Farm, Compost Bin or Bokashi?

A worm farm handles kitchen scraps in a small space and gives you concentrated castings and worm tea. A compost bin takes the bulky garden waste, and a bokashi bucket ferments the scraps worms dislike, such as meat, dairy, onion and citrus. Many households run a compost bin for the garden and a worm farm or bokashi for the kitchen. Our composting guide covers the compost side, and many councils subsidise worm farms, compost bins and bokashi systems, often after a free workshop; our free council gardening stuff page lists examples.