How to make a wormery

Video: Worm Composting: How to Make a Wormery. This guide was informed by the GrowVeg UK wormery tutorial, which walks through the full setup and covers common early mistakes. GrowVeg is a UK company (growveg.co.uk) with a solid track record for practical growing guides.

1. Choose your bin

Stacking plastic wormery kits are the simplest option. They come with a base tray to collect the liquid, two or three working trays, and a lid. Sizes range from small single-tray units for one person up to multi-tray setups that handle a full household's food waste.

You can also build your own from plastic storage boxes with drainage holes drilled through the base. It is not as tidy, but it works just as well. The GrowVeg guide suggests boxes roughly 40 by 50cm and about 20cm deep as a reasonable size to start with.

2. Prepare the bedding layer

Before the worms go in, you need a damp bedding layer for them to settle into. Torn up cardboard, damp newspaper, coconut coir, or a mix of these all work. Avoid anything glossy or printed with coloured ink.

Wet the bedding so it feels like a wrung-out sponge, not dripping. This is the moisture level you want to maintain throughout. If the bin gets too dry, the worms will slow right down or try to leave.

3. Add the worms

You need composting worms, not ordinary garden earthworms. The ones to use are red wigglers (Eisenia fetida) or tiger worms. These are surface-dwellers that thrive in decomposing organic matter, whereas garden earthworms need mineral soil and will die in a wormery.

Start with around 500g of worms, which is roughly 500 to 1,000 individuals. Order from a UK supplier - it is easy to find them online. Place the worms on top of the bedding and leave the lid off for a few minutes. The light will drive them down into the bedding, which shows they are healthy.

4. Start feeding

Wait about a week before adding food, to give the worms time to adjust. Then start with small amounts: fruit and vegetable peelings, coffee grounds, tea bags (without the staple), crushed eggshells, and torn cardboard. Bury food under the bedding layer to reduce fruit flies.

Avoid meat, fish, dairy, oily or processed foods, citrus peel in large quantities, and anything with strong flavours like onion or garlic. These either attract pests or take too long to break down. Add a small amount of food at a time and only add more once the previous lot has largely gone.

5. Manage moisture and temperature

Worms work best between about 15 and 25 degrees Celsius. In winter, move the wormery somewhere frost-free - a garage, outbuilding, or utility room works well. In a cold garage in a Kent January, the worms will slow significantly but should survive if the bin stays above freezing.

Check the moisture level every couple of weeks. If the bin is too wet, add more torn cardboard. If it is too dry, add a little water. The balance matters. A properly managed bin has almost no smell beyond a mild earthy scent.

6. Harvest the worm castings

After two to three months, the working trays will start to fill with dark, crumbly castings. To harvest, stop feeding one tray and move food to the tray above. The worms will migrate up to the food, leaving the lower tray full of pure castings.

These castings are exceptionally rich in plant nutrients. Use them as a potting mix addition, top-dressing for established plants, or mixed into compost. A small amount goes a long way. It is genuinely some of the best stuff you can put on a garden.

7. Collect and use the liquid feed

The base tray collects leachate, the liquid that drains down through the bin. Dilute it roughly ten parts water to one part leachate before using it. It is a strong liquid feed, good for watering vegetables and container plants during the growing season.

Drain the base tray regularly so it does not overflow. Some wormeries come with a tap for this. If yours does not, check every couple of weeks and empty it into a watering can.

When to call a handyman

If you want a custom timber wormery surround, a bench-height setup, or an outdoor composting area that includes a wormery and compost bays together, Richard can help with the building work. The worms and the organic side are down to you.