Indoor terracotta worm composter

Compost worms are most active between 15 and 25 °C, in material that is moist but never waterlogged, and they need a good supply of oxygen. Below 5 °C or above 30 °C, temperatures can be fatal to them, which rules out a sun-facing windowsill, proximity to an oven or radiator, and a balcony in winter. They also dislike vibration: avoid placing the unit on a washing machine or next to a fridge. A temperate kitchen, a larder, or a corner of a room away from direct light suits them perfectly, and it keeps the composter conveniently close to the chopping board.

Add your raw or cooked peelings, provided they carry no sauce or dressing, along with coffee grounds, opened tea bags, crushed eggshells, mushroom trimmings, and spent flowers. Cut peelings into small pieces, as the finer the material, the faster it breaks down. Keep out of the pot, however: meat, fish, pasta, bread and brioche, oil, milk, citrus fruit, and walnut or rhubarb leaves. Do not store fruit peelings in a bucket before adding them either: the fermentation attracts fruit flies, whereas peelings added straight away and covered with sawdust go unnoticed.

A wormery starts slowly, because the worm colony must first multiply according to the food available. Allow around 6 months before harvesting the first compost. Once the worms fill the entire ring, the cycle shortens to 3 months, and to 2 months if you add a compost activator once the pot is full, which speeds up decomposition by around 30% for one month. Without worms, composting remains purely bacterial and takes around twelve months. The compost is ready when you find almost no worms left in it, a sign that decomposition has run its course. During periods away, a break of 3 to 4 weeks without adding material causes no problem for the colony.

The worm compost produced has the appearance of very fine potting compost. It is mixed at roughly two thirds soil or compost for repotting, seedlings, window boxes and houseplants, and is best used within 6 months of harvesting. If you run an aquaponic system, it also makes an excellent nursery medium: seedlings raised in a mix enriched with worm compost develop a well-nourished plug by the time you transplant them into the grow beds. The compost itself should never be poured into the fish water, and the vermiponics guide explains how worms can live directly in a grow bed on grow medium.

At 26 centimetres in diameter and 22 centimetres tall, the composter fits on a corner of a worktop, and it weighs 5.5 kg empty, so choose its spot before you fill it. Its 8-litre ring keeps pace with the kitchen scraps of a one- to two-person household. If your household grows, a second composting ring stacks on top of the first, doubling the volume to 16 litres and catering for three to four people; the composter then stands around 37 cm tall, which is worth checking against overhead cupboards. The lid and the sawdust reservoir serve both tiers.

The worm composter arrives in three terracotta pieces, the lid, the sawdust reservoir, and the 8-litre composting ring, along with an instruction leaflet listing all accepted waste. These pieces are made by a German ceramics company less than 200 kilometres from Haguenau in Alsace, where the composter was designed; the clay then develops a patina over time, giving each piece its own distinctive shade. For a year's worth of deposits, the annual accessories pack includes two bags of coarse sawdust and two bags of activator, with or without worms depending on the version you choose.