Vermicomposting (Indoor Composting with Worms)

What it is

A household generates around 400g of food scraps a day on average. A established worm bin processes roughly that much in a week, turning peelings and coffee grounds into some of the richest compost you can get.

Vermicomposting is indoor composting powered by worms, specifically tiger or red wriggler worms (Eisenia fetida), kept in a ventilated bin with damp bedding. You feed them vegetable scraps, coffee grounds, and torn cardboard, and they convert it into dark, crumbly castings that plants love. The bin is compact, odourless when run right, and fits under a sink or on a balcony.

The worms are particular but not difficult. They want moist bedding, a roughly balanced diet of 'greens' like scraps and 'browns' like cardboard, and no citrus, onion, meat, or dairy, which either harm them or cause smells. Get the balance right and the bin smells of forest floor, not rubbish. Get it wrong, usually by overfeeding, and it goes sour, which is the single most common beginner mistake.

A starter bin costs around €30 to build from stacked storage boxes with drainage holes, plus the worms themselves at roughly €25 for a starter population. They breed to match their food supply, so the colony self-regulates over a few months.

The payoff is two streams of fertiliser. The solid castings enrich soil directly, and the liquid that drains out, diluted heavily with water, makes a potent plant feed. For anyone with houseplants or a small garden, a worm bin closes a loop that would otherwise end in the bin lorry.

How it works

A worm bin with stacking trays manages itself far more easily than a single open bin. Can-O-Worms and Worm Factory are the common ready-made versions, but a stack of two or three drilled plastic storage boxes does the same job for a fraction of the price. The worms migrate upward toward fresh food, leaving finished compost below ready to harvest.

The worms are specific. You need composting worms, Eisenia fetida, the tiger or brandling worm, not ordinary earthworms dug from the garden, which die in a bin. A starter population of around 250g to 500g establishes a working colony, available by post from worm farms. They eat roughly their own body weight in food scraps over a few days once established.

Bedding comes before food. Line the working tray with damp shredded cardboard, newspaper, and a handful of soil for grit, moist as a wrung-out sponge but never wet. Then feed gradually, burying small amounts of fruit and vegetable scraps, coffee grounds, and crushed eggshell under the bedding. Overfeeding is the classic beginner mistake: food piles up faster than the worms can process it, rots, and turns the bin sour and smelly.

The bin should never smell bad. A healthy wormery smells of damp earth, and any sour or rotten smell means too much food, too much moisture, or not enough air. Avoid meat, dairy, citrus, onion, and garlic entirely, since they either rot foully or harm the worms.

Benefits

Sustainability Learning & Discovery Garden Improvement Circular Living Relaxation Enjoyment / Fun

What you need

Here's what to gather before you start. The essentials are marked.

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Can-O-Worms or Worm City stacking system (both on Amazon)

Red wiggler worms: Original Organics or Worms Direct (500g starter pack)

Westland Coir block (for bedding, expands to fill the tray)

Damp shredded cardboard or newspaper (additional bedding)

Kitchen scrap container with lid (for collecting scraps before adding)

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Container

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Watering can for diluting worm tea (1 part leachate to 10 parts water)

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Watering can

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FAQs

Will an indoor worm bin smell bad?

No, when it is balanced, and that surprises people. A healthy bin smells earthy, like a forest floor, not like rubbish. Bad smells mean something is off, usually too much wet food waste or not enough dry bedding. I keep a good layer of shredded cardboard on top and never overfeed, and mine has never stunk out the kitchen.

What worms do I need, and can I use garden worms?

Red wigglers (Eisenia fetida), specifically, not the earthworms from your garden. Garden worms burrow deep and die in a shallow bin, while red wigglers are surface feeders that thrive in compost conditions. I started with about 500g, which is roughly 1,000 worms, ordered online for around €25. They multiply to match the food available.

What can't I put in the bin?

Meat, dairy, oily food, citrus, onion, and garlic. Meat and dairy rot and stink and attract pests, while citrus and onion are too acidic and irritate the worms. I stick to vegetable scraps, fruit peels (minus citrus), coffee grounds, crushed eggshells, and plenty of shredded cardboard. Chop scraps small so they break down faster.

How long until I actually get usable compost?

About three to six months for the first harvest. The worms work through bedding and scraps gradually, turning it into dark, crumbly castings that are superb plant food. I harvest by pushing the finished compost to one side and adding fresh bedding and food to the other, so the worms migrate over and I scoop out the castings.

Is it realistic in a flat with no garden?

Completely, and that is the point of an indoor bin. A standard bin fits under a sink or in a cupboard and processes the food waste of one or two people easily. I keep mine in a kitchen corner. As long as you do not overfeed and keep the bedding right, it stays clean, quiet, and odour-free.