Chillies are tender plants that need heat, sun and
For the widest choice of varieties, buy seeds, sowing them indoors from late winter, for harvests from mid-summer to early autumn.
Month by Month
There are hundreds of varieties of chillies, in fruit of various colours, shapes and sizes, ranging from mild to ridiculously hot. Chilli heat is measured in Scoville Heat Units (SHU), with milder varieties such as ‘Anaheim’ rated at 500–2,500 SHU, ‘Jalapeno’ at 2,500–8,000 SHU, ‘Scotch Bonnet’ at 100,000–350,00 SHU and the blisteringly hot ‘Carolina Reaper’ at 2.2 million SHU.
Heat is not just dependent on the variety though, it can also vary according to the growing conditions and stage of ripeness.
There are currently 19 chilli varieties with an RHS Award of Garden Merit (AGM), which shows they performed well in our trials – check out our list of AGM fruit and veg.
What and where to buy
Chilli seeds are widely available in garden centres and from online seed suppliers. There are also many specialist chilli seed retailers, who offer the widest choice of varieties.
Many of these sources also sell young plants in spring and early summer. These are ideal if you don’t have time to sow seeds or don’t have a suitably warm, bright place to raise good plants.
Another option is to buy grafted seedlings, which can be ordered from online suppliers for delivery from mid-April. These more vigorous plants should produce larger crops and are especially useful where growing conditions are a little cool.
Fill a small pot with seed compost, firm gently then sow a few seeds on top. Most seeds will germinate, so only sow a few more than you need, in case of losses. Cover with a fine layer of vermiculite and water carefully.
Seeds will germinate quickly in a heated propagator at 21°C (70°F) or simply put the pots on a warm windowsill. Place a clear plastic bag over each pot, secured with an elastic band, to raise the humidity.
As soon as seedlings appear, take the pot out of the propagator or remove the plastic bag. Keep plants at 16–18°C (60–64°F) in bright light and water regularly.
When the seedlings are 2.5cm (1in) tall, move each one into its own small pot of multi-purpose compost. Then, once roots begin to show through the drainage holes, move them into larger 13cm (5in) pots.
By late May, move each plant into its final 22cm (9in) pot or plant three in a standard growing bag. Add canes to keep them stable and upright.
The plants will grow and crop best if kept in a greenhouse, polytunnel, conservatory or cold frame. However, in mild parts of the country you can move them outside, once all danger of frost has passed (see Planting out, below).
Keep chilli plants indoors until the night temperature is reliably at least 12°C (54°F), usually by late May or early June. Then harden off for two to three weeks, to acclimatise them to outdoor conditions.
Chillies need your warmest, sunniest spot to produce a crop outdoors. They grow well in large containers, ideally on a sunny patio or by a south-facing wall.
They can also be planted in the ground, into well-drained, fertile, moisture-retentive soil that is slightly acid. To achieve this, dig in moderate amounts of well-rotted manure – at a rate of 5.4kg (10lb) per square metre/yard – but avoid using fresh manure or large quantities, as this can lead to lush, leafy growth at the expense of fruit. Then warm the soil with polythene sheeting or cloches for a couple of weeks before planting.
Plant the young chillies in the ground at the same level they were growing in their pot. Space them 38–45cm (15–18in) apart, depending on the variety. Dwarf varieties can be spaced 30cm (1ft) apart. Then cover with fleece or cloches to provide wind protection, preferably until the end of June.
Temperature and humidity
Chilli plants will tolerate a minimum night temperature of 12°C (54°F), but will grow better if kept above 15°C (59°F). However, temperatures over 30°C (86°F) can reduce fruiting, so keep greenhouses well ventilated and put up shading in hot weather.
Chillies like a humid atmosphere, so in hot weather ‘damp down’ the greenhouse twice a day by pouring a full watering can over the floor, then leave it to evaporate.
Water little and often to keep the soil or compost evenly moist, avoiding waterlogging and drought. Add mulch to help hold in moisture. Plants in containers can dry out very quickly, so check them regularly. Flower buds may fall off if plants get too dry.
Feed chilli plants with a high potassium liquid fertiliser weekly, as soon as flowering starts.
Pruning and Training
To encourage side-shoots, which should carry more fruit, pinch out the shoot tips once plants reach 30cm (1ft) tall.
Large plants and those in growing bags may need support. Use several canes per plant, and take care when tying in the stems, as they can be brittle.
Chillies are generally ready for harvesting from mid-summer into autumn if grown in a greenhouse. Fruiting outdoors should start by August.
Pick fruits when green to encourage further cropping. Left on the plant, they will change colour and develop a hotter flavour.
If chillies are left to ripen on the plant, new flowers won’t be produced, which can lead to a reduction in the overall harvest of 25 per cent or more.
Because mature fruits are hotter and more colourful, the smaller harvest is often considered worthwhile.
Towards the end of the season, cover outdoor plants with fleece, or bring them indoors, to help the remaining fruits develop.
Aphids are a frequent problem on chilli plants, so check shoot tips and under leaves regularly, squashing them or washing them off to prevent colonies getting established.
Red spider mites and whitefly can be problematic in greenhouses, especially in dry conditions. Young chilli plants also need protection from slugs and snails – see our tips on how to stop slugs and snails.
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