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Chillies are perennial shrubs in their native climates, but in the UK we usually treat them as annuals because our winters are too cold and too dark for them to keep growing outdoors. That means most gardeners sow fresh seed every January or February, wait months for a decent crop, and then bin the plants in autumn. If you have a cool, frost-free room going spare, though, you can keep a handful of your best plants alive through the winter and have them cropping again by early summer — often weeks ahead of anything grown from seed.
Overwintered plants also tend to be more productive. A plant that already has a well-developed root system and a thick stem will push out new growth far faster than a seedling. The trade-off is that you have to manage them carefully: a warm, centrally heated room will leave them leggy and exhausted, while a frosty shed will simply kill them. The sweet spot is a cool room that stays somewhere between about 5°C and 12°C.
Not every chilli is worth the effort. The best candidates are Capsicum chinense varieties such as habaneros and scotch bonnets, plus slower superhots like the bhut jolokia and Carolina reaper, because they take so long to fruit in our short season. Compact C. annuum types like jalapeño and cayenne also overwinter well, especially if they were strong, healthy plants in summer. Anything riddled with aphids, or that sulked all season, should go on the compost heap.
As for the room, think unheated bedroom, spare box room, glazed porch or insulated garage. An unheated conservatory can work if it does not drop below freezing at night. What you want is a space that is cool, reasonably bright and stays above 5°C. Frost is the killer, not cold itself. A simple max-min thermometer left on the windowsill for a week will tell you whether your chosen spot is genuinely safe.
Before the first frost, bring the plants indoors and give them a serious haircut. Left unpruned, they will drop leaves in the low light anyway, and the fallen foliage encourages mould and pests. Take the main stems down to roughly 15–25cm above the soil, leaving two or three healthy side shoots if you can. Use clean, sharp secateurs and cut just above a leaf node, because that is where new growth will break next spring.
At the same time, strip off any remaining leaves and any unripe fruit. Green chillies left on the plant will not ripen in a cool room and will simply sap the plant's energy. If you want to use them, try ripening the pods on a sunny windowsill indoors, or turn them into a green chilli pickle. Once trimmed, tidy the plant up further: wipe the stems with a damp cloth to remove aphids and their sticky honeydew, and check under the leaves and around the rim of the pot for overwintering pests.
Overwatering is the single most common way to lose an overwintering chilli. In cool conditions the plant is barely growing, so it drinks very little. Water sparingly — perhaps once a fortnight, or when the top few centimetres of compost feel dry — and never let the pot stand in a saucer of water. A modest drink is enough to keep the roots alive; soggy compost will rot them in a fortnight.
Stop feeding altogether from late autumn until you see new growth in February or March. At that point, resume with a weak general-purpose feed every couple of weeks, switching to a tomato feed once flowers appear. Repotting is best left until spring, though it is worth checking that the pot drains freely before you settle the plant in for winter.
If you have a greenhouse or cold frame, choose the driest, most sheltered corner. If space is tight, you can also overwinter chillies in smaller pots after trimming the roots, but take care not to overwater the reduced root ball. Some gardeners also wash the root ball free of old compost and store the bare-rooted plant in a cardboard box of slightly damp compost in a cool garage — it works, but only if the space genuinely stays frost-free.
Indoor warmth and stressed plants are a magnet for aphids, whitefly and red spider mite. Check your plants every couple of weeks, paying particular attention to the undersides of any remaining leaves and the growing tips. A squirt of dilute washing-up liquid in water, or a careful wipe with a damp cloth, will deal with small outbreaks. Quarantine any new plant before it joins the others, and keep the room reasonably ventilated to discourage mould.
Around late February or March, when daylight lengthens, you should see tiny green shoots breaking from the old stems. This is the signal to move the plants somewhere warmer and brighter — a sunny windowsill indoors or a heated propagator — and to start watering and feeding again. Pot them on if the roots have filled the container, and harden them off gradually before moving them outside once the risk of frost has passed, usually late May in most of the UK.
The reward is worth the fuss. Overwintered plants typically start flowering several weeks before seed-raised ones, which means ripe pods by July rather than September. If you only have room for a few, choose your healthiest, tastiest plants, keep them cool and dry, and enjoy a head start next season.
The Frost Corner shares practical, down-to-earth guidance on uk cold-weather gardening and seasonal home living for readers across the UK.
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