Overwintering Chilli and Pepper Plants in Scotland: Is It Worth It, and How

It is late September and the chilli by the greenhouse door still has a handful of green fruits that are not going to ripen. The lower leaves have gone yellow and are dropping, the nights are cooling and the light is shortening. You are standing there with a decision: tip it on the compost heap, or try to carry it through to spring. Both answers are defensible, and which is right depends on the plant you have, the space you can offer and the light that space gets between November and February.

What you are actually deciding

Chillies are tender plants, which is why the usual advice is to sow fresh each year. Gardeners' World states plainly that chillies will not survive the winter and that it is best to sow seeds for fresh plants each year. The RHS takes a more open line: chilli plants can be overwinteredKeeping a plant alive and intact through the cold months, whether left outdoors, moved under cover, or stored dormant. Full definition → in a heated location rather than started afresh, and doing so gives a head start on production the following summer.

A chilli left outdoors or in a cold greenhouse will die; one given warmth and light can carry on. For a Scottish grower the obstacle is not the plant's biology but what winter offers: very little daylight and low temperatures in any unheated space. Fewer leaves and slower growth in that light also make cool, damp air a rot risk.

Which plants are worth saving

Not every plant is equally good raw material.

• Chillies over sweet peppers. Sweet peppers are tender plants that grow best above 15°C and are usually grown under cover in the UK. They are a poorer bet over winter, and we would not spend scarce warm space on one.
• Cold-tolerant baccatum types. Gardeners' World describes the chilli 'Erotico' as a cold-tolerant baccatum type that overwinters well in a cool greenhouse for a second year of harvests, and says the tall 'Aji Wrecking Ball' can survive winter in a cool greenhouse. Other baccatums vary, and a "cool greenhouse" in Scotland would still need frost protection. For choosing types in the first place, see the best chilli varieties for Scotland and best sweet pepper varieties.
• Healthy plants. A plant already covered in aphids or with rotting stems will not improve indoors. Save the strongest one or two.
• A plant you would miss. A favourite variety you cannot easily replace is a good reason to keep a plant. A rooted cutting takes up far less warm space than a whole plant, and seed from the best fruit of an open-pollinated variety is the cheapest insurance.

The seed packet or plant label usually names the species (annuum, chinense, baccatum, frutescens or pubescens), but winter survival varies by cultivarA plant variety that arose or was bred under cultivation and is kept true by deliberate propagation, rather than a naturally occurring wild species. Full definition → as much as by species. If you have grown a particular type through a winter before, trust your own record over any general list.

When to bring plants in

Move the plant before the greenhouse gets cold, not after. In most Scottish gardens that means September or early October, and earlier in colder inland and northern sites, well before the first frost.

Chillies in growth want a minimum night temperature of about 12°C, and better growth above 15°C. That is a growing figure, not a winter survival figure. For plants held over winter, the RHS conservatory bands are the nearest guide:

Treat the right-hand column as a rule of thumb, not a survival figure. A porch or spare room that stays at the cool band is worth a try; a garage or shed that gets frost is not.

What this means in Scotland: an unheated greenhouse is not a winter home for a chilli, because it follows outdoor temperatures closely on a clear night. A greenhouse you can heat to the bands above is a different matter. If you do heat one, see insulating a greenhouse for winter before you commit to the heating bill. Otherwise a cool but heated spare room, porch or conservatory beats a greenhouse. Check the plant over for pests before it comes indoors, so you do not carry them onto your windowsills.

The cut-back

Prune the plant back to a manageable size and then keep it in a warm, bright place, such as an indoor windowsill or conservatory, and water it sparingly.

Cutting height varies, and some growers cut very hard. As a starting point, prune to a framework of main stems that fits your sill:

1. Pick every fruit, ripe or not. Fruit will not finish ripening on a dim windowsill and just drains the plant.
2. Remove dead, yellowing and crossing growth, and shorten the remaining branches so the plant fits your space. Leave some healthy leaf and a few buds on each stem, because a stem cut to bare wood may not restart.
3. Do not go to the extreme of a bare stump on a plant you cannot afford to lose. If you have two plants, try one pruned harder and one lighter, and note the difference.

Expect leaf drop regardless. A plant in a dim room will shed leaves as the light fades, and this is not necessarily a sign of death. Check for life by scratching the bark of a stem: green underneath is alive.

Pots and compost

Leave the roots alone unless the roots have filled the pot or the compost has gone sour and smelly. Repot only in spring, when growth restarts. If you have to refresh the compost, choose a free-drainingSoil that lets water pass through quickly rather than pooling, so roots aren't sitting in wet ground after rain. Full definition → peat-freeCompost made without peat, which is harvested from a slow-forming, carbon-storing wetland habitat that peat extraction damages. Full definition → mix, because wet, heavy compost in a cool room is the quickest way to lose a dormant plant. See DIY peat-free potting mixes and peat-free compost for mixes. A pot with real drainage holes, standing on a saucer you empty, matters more than the exact compost.

Watering

Water sparingly, and keep air moving to reduce fungal problems such as grey mould. A dormant chilli with few leaves uses very little water, so a full summer watering will drown it.

Water only when the top few centimetres are dry and the pot feels light, which in a cool room can mean a long gap between waterings, and water in the morning so the surface dries by night. Never let a pot stand in water.

Cool, still, damp air encourages botrytis, the grey mould that furs dead leaves and stems. Give the plant space, open a window on mild days if you can, and remove any leaf that drops onto the compost.

Light: the Scottish problem

Light is the hardest thing to supply. The plant has few leaves to catch it, and midwinter days at Scottish latitudes are short, with a low sun. Expect a plant on a winter windowsill to drop much of its leaf and sit almost still; that is normal, not failure. A grow light is for the plant that is losing its leaf faster than you would like, not a cure for a plant that is simply resting.

Where you put the plant matters:

• South or west-facing window: the best you are likely to have. Keep the plant close to the glass but away from cold panes at night.
• East-facing: usable, with less winter sun.
• North-facing sill: probably not worth trying. It gets no direct sun through the darkest months, and a plant there will be running on stored energy and will probably decline. The top 5 things to grow on a windowsill has better uses for that sill.

If you want more than survival, a grow light improves the odds of a plant that keeps some leaf rather than a dormant stump. Whether it is worth the cost depends on how many plants you want to save; for spectrum, set-up and running costs see LED grow lights in Scotland. For growers in the far north, growing through winter darkness in Shetland and Orkney covers the extreme end of the same problem.

Pests on an overwintered plant

A plant kept indoors through winter gives sap-sucking pests months without a cold snap or predators. Aphids, red spider mite and whitefly are the problems on chillies, particularly when growing indoors, and warm conservatory environments can be ideal for glasshouse red spider mite and glasshouse whitefly, so a warm, dry room is no different. Inspect the undersides of leaves every week and act at the first sign.

• Aphids: clusters on soft new growth.
• Whitefly: small white insects that lift off when you brush the plant.
• Red spider mite: fine webbing and speckled leaves, usually in warm, dry air. Sweet peppers, too, are prone to this in dry greenhouse conditions.

If you find a serious infestation in autumn, that is often the moment to give up on the plant.

When to give up

Bin or compost the plant if:

• the stems have gone soft, black or mouldy at the base;
• scratched stems are brown and dry all the way up;
• pests are established and treatment has not worked;
• it has not shown any bud or new leaf by the time you would normally be sowing, roughly late winter to early spring.

The restart in late winter

As days lengthen, the plant should show new shoots where leaves were attached to the stem. Do not rush it.

1. Water a little more as new leaves appear, still letting the surface dry between waterings.
2. Repot into fresh peat-free compost once new growth is clearly under way and roots fill the pot. Young seedlings move into larger 13cm pots once roots show through the drainage holes; for an established plant use a pot one size up.
3. Feed once flowering starts: use an organic, high-potassium liquid fertiliser weekly for container chillies from that point.
4. Harden offGradually getting young plants raised indoors used to outdoor conditions over 7–14 days before planting out, so cold, wind and direct sun don't shock or damage them. Full definition → before it goes into the greenhouse or outside. Follow the steps in hardening off seedlings. Plant into the greenhouse only when night temperatures allow: chillies can usually cope with about 12°C at night and grow better above 15°C. Gardeners' World gives a planting-out figure of night temperatures above 10°C. That is lower than the RHS figure, so err towards the warmer number in Scotland.

Seed is sown indoors from late winter to mid-spring because chillies need a long growing season, so a fresh seedling starts from nothing, and in Scotland the season closes early. A carried-over plant starts already grown, so it should flower before a spring-sown seedling. How much earlier depends on how well it came through the winter. If it has spent months in weak light, harden it off as carefully as a seedling. For germinationA seed sprouting: breaking dormancy and putting out its first root and shoot, given the right warmth and moisture. Full definition → temperatures see seed germination temperature in Scotland.

Saved plant or fresh seed?

Sweet peppers tip the balance further towards fresh seed: they need consistent warmth, so we would sow fresh.

Common questions

Sources