Feeding your worms: how much and how often

As a rule of thumb, a compost worm (Eisenia fetida) eats about half its body weight a day. We work on the basis that 4,000 worms weigh about 1 kg / 2.2 lb and can eat about 500 g / 1.1 lb a day. That’s only a guide, though. How much they really eat depends on the kind of food and the condition it’s in when it goes into the bin.

Worms have no teeth. They only eat food once it starts to soften and decompose. It’s much like us: we can swallow pudding far faster than a tough steak. Fresh apple cores, lettuce, green beans and carrots wait in the bin until they’ve softened. So the softer the food, the more the worms get through.

• Let it age: collect scraps for a few days in a lidded bucket so they start to break down.
• Freeze it overnight: thawed food softens quickly, and freezing also kills fruit fly eggs on the peels (a nice side effect, see fruit flies).
• Chop it small: more surface means faster eating.
• Crush eggshells to a fine powder. It adds grit and helps keep the bedding from turning sour.

There’s no need for a strict timetable, and please don’t start weighing your scraps! Feeding once a week or every other week is usually plenty. Feeding every day is fine too. The rule that matters: keep a layer of at least 5 cm / 2 in of food on the surface, and your worms will never go hungry.

Be patient. A new worm farm usually starts with about 500 worms, which grow into thousands within a few months. Feed in moderation at first. Uneaten food that piles up rots, smells and attracts flies and fruit flies. Add more as the worm population grows.

Citrus peel, onions and other sharp or acidic scraps are fine in small amounts but can sour the bin in bulk. See oranges and orange peels. Feed used coffee grounds sparingly. They’re acidic and can heat up in a thick layer. The full list, with ratings, is on the worm food rating list.

A sour or rotten smell, mould spreading over untouched food, flies, and worms climbing the walls. Stop feeding for a week, take out some of the food and mix in dry shredded cardboard. The troubleshooting FAQ covers the rest.