Building a Simple Wormery for Kitchen Scraps

Why a wormery earns its corner

A wormery is one of the few pieces of gardening kit that works as hard on a balcony as it does at the end of a long garden. You tip in vegetable peelings, tea bags and the odd wilted lettuce leaf, and the worms quietly hand back two things every small-space grower wants: a crumbly dark compost and a steady supply of liquid feed. A standard bin holds around 50 litres, which is about the footprint of a recycling box, and it will process much of a household's raw kitchen waste over a year.

The worms themselves — brandling or tiger worms, sometimes sold as Eisenia fetida — are undemanding. Give them damp bedding, cool temperatures and a regular scattering of scraps, and they will breed to fit the space available.

Choosing and siting your bin

Most commercial wormeries are stacked trays with a sump and a tap at the bottom. You can make your own from a pair of lidded plastic storage boxes, one nested inside the other to catch the liquid. Either way, a tap fitted two to three centimetres above the base stops the bedding sitting in a puddle — waterlogged worms drown or climb the walls.

• Drill a ring of 8–10 mm ventilation holes around the upper sides and across the lid, then cover them with fine mesh to keep fruit flies out.
• Site it in shade and away from frost: a north-facing wall, a shaded corner of a yard, or a sheltered balcony spot beside a shed.
• Avoid full sun. A dark bin on a July afternoon can cook a colony in an hour.
• Aim for 15–25°C. Worms slow below 10°C and stop feeding below 5°C.
• Stand the bin on bricks or a tray to catch drips, especially on a balcony where staining matters.

Setting up the bedding

Fill roughly two-thirds of the bin with bedding before the worms arrive: shredded cardboard, newspaper (skip the glossy supplements), coir, and a couple of handfuls of garden soil or finished compost to add grit and microbes. Dampen it to the texture of a wrung-out sponge — squeeze a handful and a drop or two of water should appear.

Add 250–500 g of worms to start. A 50-litre bin will happily settle at around 1 kg once the colony builds. Leave them a week to settle in before the first feed, and sprinkle a little lime mix or crushed eggshell every month or so to keep conditions sweet.

Feeding rules that keep worms happy

Start small: about a litre of scraps a week is plenty for a standard bin. Chop things roughly — smaller pieces break down faster — and bury each helping in a different corner, covering it with bedding to keep flies away.

• Good: vegetable and fruit peelings, tea leaves and plastic-free tea bags, coffee grounds, crushed eggshells, salad leaves, soft plant trimmings, torn cardboard.
• In moderation: citrus peel, onion and garlic skins. Fine in small amounts, but they acidify the bin and worms dislike a sour bed.
• Avoid: meat, fish, dairy, oily or cooked food, pet faeces, treated wood shavings and glossy paper.

Keep a lidded caddy on the kitchen counter so scraps go in fresh and flies never find them. If you are adding a lot of wet material, balance it with torn cardboard.

Harvesting castings and liquid feed

Drain the tap every week or two. That dark liquid is strong stuff — dilute it one part to ten parts water before feeding tomatoes, peppers, courgettes or container plants, and never pour it on neat.

Castings are ready when the bin is mostly dark and crumbly, usually after three to six months. The easiest method is to push everything to one side, add fresh bedding and food to the other, and let the worms migrate across over a few weeks. Alternatively, tip the contents onto a tarpaulin in bright light, shape it into small cones, and lift the castings off the top as the worms burrow down.

Use the finished castings as a mulch, or mix one part castings to three parts potting compost for a rich seed and container blend.

Sorting out common wobbles

• Sour or rotten smells: usually too wet, or too much food at once. Add shredded cardboard and pause feeding for a fortnight.
• Fruit flies: scraps left on the surface. Bury deeper, cover with damp cardboard and keep the lid on.
• Worms climbing the walls: often a sign of waterlogging or acidity. Add lime mix and dry bedding.
• Worms disappearing: check drainage and temperature. Standing water is the usual culprit.
• Winter: insulate the bin with bubble wrap or old sacks, move it into a shed or garage if you can, and feed less. In a hard frost the colony may slow to nothing — that is normal, and it will pick up again in spring.

Keep it damp, cool and fed little and often, and your bin will quietly turn a week's peelings into something worth pouring on next summer's tomatoes.