Bedding is the material composting worms live in, as opposed to the food they are given. A good bedding holds moisture, lets air through and is rich in carbon, giving the worms a stable habitat between feeds.
1Bedding and food
Bedding is carbon-rich and breaks down slowly; food scraps are wetter and richer in nitrogen. Worms eat both, but the bedding is what buffers the bin. Too much food for the amount of bedding makes a bin heat up, turn sour and smell, and the worms try to leave.
2Materials
Coconut coir holds water well, has a near-neutral pH and does not compact, but it contains almost no nutrition on its own. Shredded cardboard adds carbon and structure and soaks up excess moisture; corrugated card keeps air pockets open, while plain paper tends to mat together. A handful of castings or mature compost brings in the microbes that start the breakdown.
Mixing materials gives a better structure than any one of them alone. Avoid glossy or coloured print and fresh manure, which can heat up.
3Moisture and air
Earthworms breathe through their skin, which only works while it stays moist. The bedding should feel like a wrung-out sponge: a squeezed handful releases a drop or two, no more. Too dry and the worms dehydrate; too wet and the bin goes anaerobic.
4Not for mealworms
Earthworm bedding is deliberately damp. Mealworms and superworms need the opposite, a dry grain substrate, and would mould and die in worm bedding. See Mealworm substrate.