Starting a Wormery for Kitchen and Garden Waste

Why a Worm Bin Earns Its Space

A wormery is one of the few bits of kit that pulls its weight twice over. Tip in the peelings from a week's cooking and you get back two things: a steady supply of liquid feed for container plants, and dark, crumbly castings that make a fine top dressing for pots, grow bags and raised beds. For anyone gardening in a courtyard, on a balcony, or on a half plot with no room for a compost heap, that compactness matters. A tidy stacking bin will sit happily in the corner of a potting shed or beside the water butt on an allotment, quietly working away from March to October.

You are not keeping ordinary garden earthworms. You want brandling or tiger worms, the striped ones that thrive in rotting material rather than soil. These work shallow, breed fast, and have a healthy appetite for the sort of soft kitchen waste that turns a compost heap into a slimy mess.

Choosing a Bin and a Spot to Keep It

Stacked tray systems are the easiest to live with: as one tray fills, you add the next above it, and the worms migrate upwards through the drainage holes, leaving finished castings behind. A drum or dustbin with a tap at the base works well too, and you can drill your own from a lidded storage box for very little outlay. Whichever you choose, make sure there is a sump for liquid to collect and a tap to draw it off, or a tray underneath that will not overflow onto the shed floor.

Position is more important than the type of bin:

• Shade, always. Direct summer sun will cook them. A north-facing spot, a gap under a bench, or the shaded end of a potting shed is ideal.
• Above frost. Worms slow to a standstill below about 5°C and can die if the bin freezes solid. On an allotment, stand the bin on a wooden pallet and wrap it in hessian, bubble wrap or an old wool blanket from November onwards.
• Handy for the kitchen. If the walk to the bin involves wellies and a torch, you will stop doing it. Keep a lidded caddy in the kitchen and empty it weekly.
• Level and stable. A full tray system gets surprisingly heavy once it is wet.

Setting Up and the First Feed

Fill the base tray with bedding before the worms arrive. Moistened coir, shredded plain cardboard, torn egg boxes, or a mix of all three work well. Aim for the texture of a wrung-out sponge — damp but never dripping. Add a handful or two of garden soil or finished compost to introduce grit and microbes into their guts; worms use grit to grind their food.

Scatter the worms over the bedding and leave the bin lid off for an hour or two so they have a reason to burrow down. Keep the lights on and they will settle quickly. Give them nothing at all for the first week apart from a little damp bedding. After that, start with a thin layer of scraps, no more than a couple of centimetres deep, and build up slowly as you see the bin keeping pace.

What to Feed and What to Avoid

Worms are not fussy, but a bin is not a bin liner either. Roughly half of what you add should be bedding material — torn cardboard, paper, spent potting compost — to keep the bin aerated and stop it turning sour.

• Good: vegetable and fruit peelings, tea leaves and bags (plastic-free ones), coffee grounds, crushed eggshells, soft plant stems, dead houseplant leaves, small amounts of grass clippings.
• In moderation: citrus peel, onion and garlic skins, brassica stalks. All fine in small amounts, but too much acid will upset the bin.
• Avoid: meat, fish, dairy, cooked food, pet faeces and glossy printed paper. These smell, attract rats, and can carry disease.

Chop or freeze scraps before adding them. Freezing bursts the cell walls and speeds up the process by a fortnight or more. A light sprinkle of crushed eggshell or garden lime every few weeks keeps the pH sweet and prevents the bin going acidic and smelly.

Harvesting Castings and Using the Liquid

Drain the sump tap every week or two. That dark liquid is strong stuff — dilute it one part to ten parts water and use it on tomatoes, courgettes, dahlias and anything in a pot. Undiluted it will scorch roots.

Castings are usually ready eight to twelve weeks after a tray is filled. To harvest, stop feeding that tray for a week, then push the contents to one side and add fresh food to the clear side. Most of the worms will migrate across within a few days, leaving you free to lift out the finished side. Spread the castings on top of container compost as a mulch, or mix two parts compost to one part castings for a gentle, slow-release feed that will not burn young plants.

Troubleshooting and the Winter Slowdown

If the bin smells sour, you are overfeeding or it is too wet. Stir in dry shredded cardboard and hold off the scraps for a fortnight. Worms climbing the sides usually mean waterlogged conditions; check the tap is not blocked. Fruit flies are a sign of exposed food, so always bury scraps under the bedding. If the population is booming by midsummer, split the bin or pass a tubful on to a plot neighbour — there is always someone who wants to get started.

Come late autumn, feed less and insulate well. The worms will keep ticking over in a sheltered shed, and by March they will be hungry again and ready for another season of turning your peelings into something worth having.