A practical guide to growing chillies in Britain and other cool climates: when to sow, germination temperatures, pots and compost, feeding, pollination, pests and harvest.
The short answer¶
Chillies need a long, warm season, and a British summer is short and cool. So start early — sow indoors between January and March, the hottest types first — give the seeds warmth to germinate (about 20–30 °C), grow them on in the brightest spot you have, and plant them out or move them to a greenhouse only when night temperatures stay above about 10 °C, usually June. Grow them in pots of 5–10 litres, feed with a high-potash tomato feed once they flower, and pick regularly from July. Mild, quick-maturing varieties can succeed on a sunny patio; the Caribbean and superhot types really want a greenhouse, polytunnel or conservatory.
Choosing what to grow¶
All cultivated chillies belong to the genus Capsicum, in the nightshade family (Solanaceae). Five species are grown, and the species tells you a lot about how a plant will behave.
| Species | Examples | Season | Notes for cool climates |
|---|---|---|---|
| C. annuum | jalapeno, cayenne, poblano, Padrón, Kashmiri, paprika types | Moderate | Easiest; many are compact and quick |
| C. frutescens | Tabasco, many bird's eye types | Long | Bushy, prolific, fairly easy |
| C. chinense | habanero, scotch-bonnet, ghost-pepper, carolina-reaper | Very long | Slow to germinate and ripen; greenhouse strongly advised |
| C. baccatum | aji-amarillo | Long | Large, tall plants; productive in a greenhouse |
| C. pubescens | Rocoto, manzano | Long | Hairy leaves, black seeds; tolerates cooler conditions than the others |
Beginners do best with a compact annuum variety. Superhots take many weeks longer to produce ripe fruit and often fail to ripen outside. For heat levels see the scoville scale.
Calendar¶
| Month | Task |
|---|---|
| January–February | Sow C. chinense and other slow types in a heated propagator |
| February–March | Sow annuum varieties |
| March–April | Prick out seedlings into 7–9 cm pots; grow on in bright light, 18–25 °C by day |
| April–May | Pot on into 1–2 litre pots, then final pots; harden off gradually |
| June | Move outdoors (sheltered, sunny) or into greenhouse beds or pots |
| June–September | Water, feed weekly, support stems, pollinate indoor plants |
| July–October | Harvest; bring plants under cover before first frost |
| October–November | Overwinter the best plants (see overwintering chillies) |
Sowing and germination¶
Sow seeds 5 mm deep in small pots or cells of seed compost, keep them moist (not soggy) and warm. A heated propagator or a warm spot (not directly on a radiator) makes all the difference: annuum types typically germinate in one to two weeks at around 25 °C, while chinense types can take three weeks or more and germinate poorly in cooler conditions. Once seedlings appear, give them as much light as possible immediately, or they will stretch into weak, leggy stems. A windowsill in February is marginal; a grow light for the first few weeks helps greatly.
Pots, compost and potting on¶
Pot on in stages rather than straight into a huge pot, which stays cold and wet. Use a good peat-free multipurpose compost, ideally with some added perlite, or a soil-based compost for large plants. Final containers of 5–10 litres suit most varieties; tall baccatum and big chinense plants appreciate more. Grow bags work, with two or three plants per bag. Stake taller plants, as a heavy crop can snap stems.
Warmth, light and hardening off¶
Chillies stop growing below about 10–12 °C, and prolonged cold stunts plants. Before moving them outdoors, harden them off over a week or two — outside by day, in at night — to toughen them to wind and full sun. On a patio, the warmest sunny spot against a south-facing wall is best. In a greenhouse, ventilate on hot days: temperatures above about 30–32 °C can cause flowers to drop without setting fruit.
Watering and feeding¶
Water thoroughly, then allow the top of the compost to dry a little before watering again. Chillies dislike waterlogged roots more than they dislike a brief dry spell. Once the first flowers appear, feed weekly with a high-potash liquid feed (tomato feed), which encourages flowers and fruit rather than leaves. Many growers believe that slightly drier conditions as the fruit ripens intensify heat; there is some basis for stress affecting capsaicin levels (see capsaicin), but variety matters far more than technique.
Pollination¶
Chilli flowers are self-fertile, and outdoors wind and insects do the job. In a still greenhouse or on a windowsill, fruit set improves if you tap the plants or dab each open flower with a small soft paintbrush every day or two. Different varieties grown together can cross-pollinate, but this only affects seeds saved from the fruit, not the fruit itself.
Pests and problems¶
| Problem | Signs | What to do |
|---|---|---|
| Aphids | Clusters on shoots and under leaves; sticky leaves | Squash, rinse off, encourage ladybirds and hoverflies |
| Red spider mite | Fine mottling, webbing, in hot dry greenhouses | Raise humidity, damp down paths; biological control available |
| Whitefly | Clouds of tiny white insects | Sticky traps, biological control |
| Slugs and snails | Holes in leaves and fruit outdoors | Protect young plants; night patrols |
| Flower drop | Flowers fall without setting | Usually heat, cold or irregular watering |
| Blossom end rot | Sunken dark patch at fruit tip | Irregular watering; keep moisture even |
Harvesting¶
Chillies can be picked green (unripe) or left to ripen to red, yellow, orange, brown or purple, depending on variety. Ripe fruit is usually sweeter and more complex, and often hotter. Cut rather than pull, to avoid snapping branches. Regular picking encourages the plant to set more fruit. At the end of the season, green fruit may ripen if the whole plant is hung upside down indoors. Glut? See drying herbs (the same principles apply), fermenting chillies, making chilli oil and hot sauce.
⚠️ Handling hot chillies
Wear gloves when handling and cutting superhots, and do not touch your eyes afterwards. See handling chillies safely.
Common mistakes¶
- Sowing too late. A May-sown habanero may not ripen before autumn.
- Too little light for seedlings, producing tall, floppy plants.
- Overwatering in cold weather.
- Feeding with high-nitrogen fertiliser: lots of leaves, few chillies.