How to protect your wormery from cold and heat

Your compost worms are living creatures: unlike a garden compost heap, which barely notices the seasons, your wormery needs a little attention when the thermometer goes haywire, in either direction. Don't worry, the right habits are simple. Here is how to protect your worms from the cold in winter and from the heat in summer.

What temperatures can your worms tolerate?

Your worms work and breed best between 15 and 25 °C. Below 15 °C, their activity gradually slows; below 5 °C, they go into hibernation and stop processing material. The real danger begins below 0 °C, where frost becomes fatal. At the warm end, keep an eye on things and moisten the bedding from 35 °C if it dries out, with the real danger starting above 45 °C. Between these two extremes, your worms adapt: what you should mainly try to avoid is a sudden, sharp change, rather than the temperature itself.

Protecting your wormery from the cold in winter

The best approach is still to choose the right spot from the outset: a wormery kept indoors (kitchen, utility room, cellar, insulated garage...) gets through winter without any particular difficulty. We cover every possible location in our guide Where to put your wormery

Good news: a well-set-up wormery copes with the cold better than you might think. Your worms, especially when there are plenty of them, along with the fermentation of their waste, give off a little heat themselves, which keeps the temperature inside the bin above the outside temperature. A well-populated, active wormery can therefore easily cope with ambient temperatures dropping to around -5 °C without you needing to step in.

If yours stays outdoors, on a balcony or in an uninsulated garage, a few precautions are needed as soon as ambient temperatures fall below -5 °C: move it closer to a sheltered wall, insulate it by covering it with a blanket, mulch or a tarpaulin, or, if possible, bring it indoors temporarily until temperatures rise again. If your model has ventilation holes in the lid, also avoid leaving it out in the rain: water can seep straight in, with the risk of drowning your worms.

Willy's tip

Adding fresh waste naturally generates a little heat, as decomposition is a process that gives off warmth. Feeding a little more generously than usual just before a forecast cold spell helps your worms get through it better — without overdoing it, though: your usual feeding routine remains the rule.

If you use an in-ground wormery, the surrounding soil already provides good natural insulation: we explain the specific precaution to take with its lid in our guide The in-ground wormery

Protecting your wormery from the heat in summer

In summer, the rule is simple: never in full sun. A wormery kept outdoors must stay in the shade, and an indoor model should never be completely shut away without ventilation, as a closed cupboard in hot weather quickly encourages unpleasant smells — we explain this in our guide Where to put your wormery

If the bedding does dry out despite everything, since heat that is too dry can weaken your worms, moisten it as a one-off by spraying on a little water.

Remember too to pause feeding for as long as the heatwave lasts: the fermentation of fresh waste gives off heat itself, which makes the situation inside the bin even worse — the exact opposite of the winter tip we gave above. Go back to your usual feeding routine as soon as temperatures drop again — we explain this routine in our guide What earthworms eat

Willy's tip

If a heatwave is forecast, spraying a little more water than usual, combined with temporarily moving the wormery to the coolest, darkest spot in your home, is more than enough to see it through.

Pop a frozen bottle of water into the wormery — in a new tray if you have a free one, otherwise in the active tray, ideally wrapped in a cloth to protect the bedding from direct contact. It stays cold for a long time and keeps your worms cool all day; simply replace it every 1 to 3 days depending on the temperature.

Warning signs to look out for

A few signs show that your worms are suffering from a change in temperature: they cluster together in a ball instead of moving normally through the material, climb up towards the lid, or an unusual number suddenly die. If this happens, the first thing to consider is precisely the temperature — well before looking at feeding or moisture. We cover all the common problems and their solutions in our guide to common problems and solutions.

In summary

Between 15 and 25 °C, your worms are fully active and need no particular attention. Outside this range, a few simple steps are enough: the right location from the outset, a cover or a temporary move during very cold weather, and shade and light moistening during hot spells. The key is to keep an eye out for extreme swings, which are far rarer indoors than outdoors.

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