Overwintering

Chillies are perennial. We grow them as annuals because the British season is too short for anything else, but kept alive and frost-free a chilli plant will crop again the following year, and crop earlier.

That head start is the point of the exercise. A seed sown in February spends until July building a plant before it puts any energy into pods. An overwintered plant already has the roots, the wood and the framework, so it flowers weeks ahead and fruits over a longer window. For the slow species that difference decides whether you get a real crop or a handful of pods in October.

Which plants are worth keeping

Not all of them.

Species	Verdict
annuum	Rarely worth it. Fast and cheap from seed, and second-year plants often sulk.
chinense	The best case. Slowest from seed, so the head start is worth most here.
baccatum	Good. Vigorous, and they make large, productive plants in year two.
pubescens	The obvious one. Genuinely perennial and the most cold-tolerant of the five.
frutescens	Worth a go, though tabasco types get leggy by the second year.

Condition matters more than species, though. A plant that struggled all summer will not improve over winter, and a badly congested old plant can be worse than a fresh seedling. Keep the ones that grew well.

When: before the first frost

Frost kills a chilli outright. Bring plants in when night temperatures start dropping below about 10°C, which across most of the UK means late September into October, earlier in the north and Scotland, sometimes into November on the south coast. Do not wait for the forecast to mention frost. By then the plant has already sat through weeks of cold, wet nights it did not need.

Pick everything first, ripe or not. Pods left on the plant keep drawing energy that the roots need.

Cut it back hard

Harder than feels reasonable. Take the plant down to a bare framework: the main stem and the first fork or two, roughly 10-15cm, with short stubs where the branches were. Leave a few leaves if you like, though most will drop anyway.

The point is less foliage to support in poor light, and far fewer places for pests to hide. A smaller plant is also easier to fit somewhere frost-free, which tends to be the real constraint.

While the plant is out, knock it from its pot, trim the outer roots and repot into something a size smaller with fresh compost. A large pot of old wet compost around a dormant root ball is the quickest route to rot.

Check for pests before it comes indoors

This is where most overwintering attempts fail, and it is not the cold that does it.

Aphids, whitefly and spider mites come inside with the plant. In a warm house with no predators and no weather they breed all winter without a check, and by February you have an infested plant standing next to your houseplants. Inspect the leaf undersides and the joints where branches meet the stem. Wash the plant down, treat anything you find, then keep it away from other plants for a fortnight and look again.

If a plant is badly infested, compost it. A replacement seedling costs less than the problem does.

Where to keep it

Cool, bright and frost-free, somewhere around 7-15°C.

A porch, an unheated spare room, a conservatory or a greenhouse with a frost heater all do the job. Two places that do not:

• A warm living room. Heat plus weak winter light produces pale, drawn growth that is no use to anyone and attracts pests.
• A dark garage or shed. Some growers store plants near-dormant in cold darkness and get away with it, but the margin is narrow and a hard frost in an uninsulated garage still kills.

An unheated greenhouse on its own is not enough in most of the UK.

Water almost nothing

More overwintered chillies are killed by wet compost than by cold.

A leafless plant that is barely growing uses almost no water. A small drink every two or three weeks, enough that the compost never goes bone dry, is plenty. No feed at all until spring. Let the pot feel light in the hand before you water it again.

By January it will look dead: bare stems, no movement, nothing. Scratch the bark with a thumbnail and green underneath means it is fine.

Waking it up

From late February, as the light comes back, move it somewhere warmer and brighter and start watering properly again. Wait until you see new growth before the first feed, then pot it on into fresh compost.

It will be weeks ahead of anything you sow this year. It still needs hardening off before it goes back outside.

Is it worth it

Some of them will not make it, and you will spend four months tending what looks like a dead twig in a pot. For an annuum that takes twelve weeks from seed, that is a bad trade. For a chinense, it is often the only way to get a full crop out of a British summer.