Why a wormery earns its place in a small garden

A wormery is one of the quietest, most productive bits of kit you can add to a British garden. Unlike a traditional compost heap, which needs a critical mass of material and regular turning, a wormery will happily process vegetable peelings, tea leaves, coffee grounds and crushed eggshells in a space no bigger than a wheelie bin. The worms do the work: tiger worms, usually Eisenia fetida, munch through scraps and produce two valuable things — crumbly dark castings and a concentrated liquid feed that drains from the base.

For anyone with a small plot, an allotment, a courtyard or even a balcony, that is a serious amount of value from what would otherwise go in the bin. You get a steady supply of soil improver, a free liquid feed for tomatoes, courgettes and herbs, and the quiet satisfaction of turning kitchen waste into next year’s harvest.

Choosing and siting your wormery

Most domestic wormeries are stackable trays with a sump and a tap at the bottom. The worms start in the lower tray and migrate upwards as they finish the food, leaving castings behind. You can also use a single bin with a drainage tap, but trays make harvesting far easier. Buy one sized to your waste: a two-person household generates roughly 1–2 litres of suitable scraps a week, so a three- or four-tray system is usually ample.

Site it somewhere sheltered and accessible. A shady spot beside a shed or against a north-facing wall is ideal. Avoid full sun in summer, which can cook the worms, and exposed frost pockets in winter. A garage, outbuilding or covered porch can work well — worms tolerate cool conditions but not freezing or waterlogged ones.

• Drainage: stand the wormery on a firm, level surface so the tap stays clear.
• Access: leave room to lift trays and fill the top one.
• Temperature: aim for 15–25°C; below 10°C the worms slow down, and below 5°C they may struggle.
• Protection: keep the lid secure against rain, rats and foxes.

Setting up: bedding, worms and the first scraps

When your wormery arrives, set up the bedding before the worms go in. A mix of shredded paper, cardboard, coir and a little finished compost or leaf mould gives the worms somewhere moist and dark to settle. It should feel like a wrung-out sponge — damp but not dripping. Add the worms gently on top; they will burrow down within a few hours.

Leave them for a week before feeding. Then add a small handful of scraps, buried in one corner. As the worms multiply, increase the amount. A good rule is to feed little and often, and never let uneaten food build up. If the tray smells sour or attracts fruit flies, you are overfeeding or the bedding is too wet.

• Chop scraps small — faster breakdown, less pest interest.
• Add a handful of shredded cardboard with each feed to keep air and carbon levels up.
• Crush eggshells or add a sprinkle of lime mix if your wormery becomes acidic.
• Keep the lid on and the bedding moist, but never sodden.

What to feed your worms — and what to keep out

Worms are not fussy, but they do have limits. Fruit and vegetable peelings, tea leaves, coffee grounds, torn cardboard, dead houseplant leaves and crushed eggshells are all excellent. Cooked food, meat, fish, dairy, oily sauces and dog or cat faeces should stay out — they smell, attract vermin and can upset the wormery. Citrus, onion and garlic are fine in small amounts, but too much can make conditions acidic.

Foragers can also add small quantities of wild leaves such as dandelion, nettle and chickweed, provided they are clean and not sprayed. Avoid anything tough or woody unless it has been shredded, and never add diseased plant material or weeds that have gone to seed.

• Good: vegetable peelings, apple cores, banana skins, plastic-free tea bags, coffee grounds, soft plant trimmings.
• In moderation: citrus peel, onion skins, garlic, cooked vegetable scraps without oil.
• Avoid: meat, fish, dairy, bones, oily food, pet waste, glossy magazines, treated wood.

Harvesting castings and liquid feed

The liquid feed collects in the sump. Drain it every week or two — more often in warm weather — and dilute it at roughly one part worm tea to ten parts water before using it on hungry crops. Undiluted, it is strong enough to burn roots. Use it on tomatoes, courgettes, runner beans, fruit bushes and container plants.

Castings are ready when a tray is dark, crumbly and mostly free of recognisable scraps. Move the worms on by placing fresh food in the next tray up; they will migrate through the holes. Then empty the finished tray and use the castings as a seed-sowing mix, a top dressing for borders or a nutrient-rich addition to homemade potting compost. A little goes a long way — one part castings to four or five parts soil or compost is plenty.

Through summer, keep the bedding damp and the unit shaded. In winter, worms slow down, so insulate the wormery with old carpet or straw and feed less. Check the tap after rain, and if a sour smell or fruit flies appear, add dry shredded card and hold back on scraps until things settle.