Worm farms: setting one up and keeping it happy

A worm farm is one of the easiest ways to turn kitchen scraps into garden food. It fits on a balcony or in a small courtyard, and doesn't smell when it's running well. The worms do the work. Your job is to feed them sensibly, keep them damp and keep them cool.

Choose your set-up

Stacking tray farms

The most common home worm farm is a stack of plastic trays with a tap at the bottom. Worms live in the working tray, and when it fills you add a new tray of food on top. The worms move up to the fresh food over a few weeks, leaving the castings below for you to harvest. Liquid drains to the base and comes out the tap.

Good for: small spaces, tidy harvesting, beginners.

Bathtub or large box farms

An old bathtub, laundry trough or large wooden box makes a roomy worm farm. Put a plug of mesh or shade cloth over the drain hole, set it on a slight slope with a container under the outlet, and fill it with damp bedding. Bigger farms handle more scraps and hold their temperature better than small ones.

Good for: big households, gardeners with more space.

In-bed worm towers

A worm tower is a tube, often a length of wide PVC pipe or a bucket with holes drilled in the sides, buried upright in a garden bed with the top sticking out and a lid on. You put scraps in the top and worms come and go between the tower and the bed, spreading castings straight into the soil.

Good for: feeding veggie beds directly, with no harvesting.

Compost worms, not garden earthworms

Worm farms need compost worms, not the earthworms you dig up in the garden. They are different animals with different habits.

Common compost worms sold in Australia include red wrigglers, tiger worms and Indian blues. They are often sold as a mix. Buy them from a nursery, hardware store or worm farmer. A starter box of about 1,000 worms is a common amount, and the population will grow to suit the food you give them.

Setting it up

1. Pick a shady, sheltered spot. Under a tree, on the south side of the house or in a garage or carport works well.
2. Add bedding. Fill the first tray with moist bedding such as shredded newspaper or cardboard, coconut coir or aged compost. It should feel like a wrung-out sponge.
3. Add the worms. Spread them on the bedding and leave the lid off for a little while in the shade. They'll burrow down away from the light.
4. Cover them. Lay a damp hessian bag, an old towel or a few sheets of wet newspaper on top. This keeps moisture in and light out.
5. Feed lightly at first. Start with a small handful of scraps and wait until most of it is eaten before adding more.

What to feed and what to avoid

Worms eat best when food is chopped small and starting to break down.

Good food:

• Most fruit and vegetable scraps.
• Tea leaves and coffee grounds, in moderation.
• Crushed eggshells, which also help balance acidity.
• Shredded paper and cardboard, without glossy coatings.
• Small amounts of soaked bread or cooked plain grains.

Avoid or limit:

• Citrus and onion family (onion, garlic, leek): too acidic or strong for most worm farms in any quantity. A little now and then is fine.
• Meat, fish and bones: they rot, smell and attract flies and rats.
• Dairy and oily food: small amounts only, if at all.
• Garden prunings and weeds with seed heads: better in the compost bin.

Feed what the worms can clear in a few days. Overfeeding is the most common cause of problems.

Keeping worms cool in an Adelaide summer

Heat is the biggest worm-farm killer in Adelaide. Compost worms are happiest at mild temperatures, roughly in the high teens to mid-20s. Once a bin gets much above 30 degrees they struggle, and a farm sitting in the sun on a hot day can cook its worms.

• Keep the farm in full shade all day, never on a hot concrete or brick surface in the afternoon sun.
• Move it somewhere cooler, such as a garage, laundry or shed, before a heatwave.
• Keep the bedding moist, and lay a wet hessian bag or towel on top.
• On very hot days, put a frozen water bottle in the top tray.

In winter, worms slow down and eat less. Feed less and keep the lid on.

Moisture

Worms breathe through their skin, so the bedding must stay damp. It should feel like a wrung-out sponge. If it's dry, sprinkle water over it. If it's soggy and smelly, add dry shredded paper and leave the tap open so liquid can drain.

Common problems

Harvesting

When the bottom tray is full of dark, crumbly castings with little food left in it, it's ready. Lift it out, pick out any stragglers and return them to the farm. For what to do with the castings and liquid, see the guide to worm castings and worm tea.