How to grow chillies

A chilli’s heat is measured on the Scoville scale, a test created in 1912, in which the more water needed to dilute a chilli solution before a human taster can no longer detect the chilli determines the number of Scovilles. Today, testing is done by machines. A score of around 3,000 Scovilles is deemed hot, with record-breaking chillies such as 'Carolina Reaper' topping two million mark.

Many chilli varieties are available to buy in supermarkets but you will have a much greater range to choose from if you grow chillies yourself. They're very easy to grow from seed, and grow best in containers, which means they are perfect for a sunny patio or balcony. You can also buy ready-grown chilli plants at the garden centre in spring.

All chillies are bred from just five species:

• Capsicum annuum – the most common chilli species, from which sweet and paprika peppers originate.
• Capsicum baccatum – includes the aji family of chillies, popular in Peruvian dishes.
• Capsicum chinense – a hot variety of chilli, from which we have habanero and scotch bonnet chillies.
• Capsicum fruitescens – where tabasco Thai-style chillies come from.
• Capsicum pubescens – these are hot chillies with distinctive black seeds.

Several online nurseries specialise in chilli seed, offering a range of interesting and unusual varieties you can use in different dishes, from Mexican salsas to Thai curries.

How to grow chillies

Sow chilli seed indoors as early as January if you have a heated propagator, or from March if you don't. Transplant seedlings into individual 7.5cm pots when the first true leaves appear. Eventually, transplant them into 30cm pots of peat-free, multi-purpose compost. Wait until all risk of frost has passed before moving them to their final growing positions outside, in a sunny spot. For the hottest chillies, grow in a greenhouse. Chillies are tender plants, so will not survive the winter. It's best to sow seeds for fresh plants each year.

More on growing chillies:

• 12 chillies to grow
• How to store chillies
• Hot chillies to grow

Chillies: jump links

• How to sow chilli seed
• Caring for chillies
• Six steps to hotter chillies
• Harvesting chillies
• Storing chillies
• Problem solving
• Chilli varieties to grow

How to sow chilli seed

Chillies need a warm, sunny spot for the best results and the hottest chillies. Ideally, grow them in a greenhouse or raise them in pots on a south-facing patio or windowsill. Chillies need a long season to grow, so it's best to sow seed as early as January in moist, peat-free multi-purpose compost, and keep in a heated propagator under a growing light, to prevent seedlings going leggy (sow seed in March if you don't have a heated propagator). Pot on into individual pots when the first true leaves appear. Keep potting on if growing in pots or plant out into the greenhouse when night temperatures exceed 10ºC – ensure the soil or compost is free-draining. Feed weekly with a high potash fertiliser once plants have started flowering, and harvest chillies as and when they appear.

How to care for chillies

Once planted out, chillies require very little attention. Pinch out the growing tips when plants are about 20cm tall to encourage bushy growth. Tall varieties may need staking.

Water your chilli plants little and often. As soon as the first flowers appear, feed weekly with a high-potash liquid fertiliser such as tomato feed.

In hot weather, mist chilli plants to increase humidity and deter spider mites.

Six steps to hotter chillies

If you want to grow chillies with a bit of bite, there are plenty of tricks you can employ. Getting the right growing conditions is vital – the hotter the growing conditions, the hotter the chilli, which is why they grow well in hot parts of the world.

Matt Simpson of Simpson’s Seeds has grown some of the UK’s hottest chillies, named ‘Katie’ and ‘Lucy’ after his daughters. He’s employed some unusual tricks to increase the heat of his fruits.

He has discovered that by stressing plants – by damaging them, denying them food and water, subjecting them to extreme heat and even shouting at them – you cause the plant’s natural defences to kick in and make the chillies spicier in a bid to stop them being eaten by animals. Here are his six top tips:

1. Choose a hot variety

There are hundreds of varieties of chillies, with differing heat levels. The very hottest varieties, such as ‘Bhut Jolokia’ are slow growing and need heat and humidity, so grow them indoors for a decent crop. Discover eight hot chillies to grow.

2. Start growing early

Even the easiest chillies need a long season to give plants plenty of time to grow, flower, fruit and ripen, and the hottest varieties need sowing as early as January. If you miss the boat, or want to give super-hot varieties a head start, grow from plug plants rather than seed.

3. Give them heat

For the biggest crop, grow under cover, preferably in a greenhouse or polytunnel, but a bright, sunny kitchen windowsill is also good. If you have to grow them outside, give plants a warm, bright, sheltered spot.

4. Stress your plants

Matt Simpson is certain that stress increases the amount of capsaicin (the compound that produces the burning sensation) in the fruit and that the most effective way to do this is to abuse the plant by snapping off stems, leaves and fruit as soon as fruit starts to set. This mimics the damage caused by predating animals. It will result in a decreased yield but hotter chillies.

5. Don't feed

Not feeding plants is another way to put them under stress and increase capsaicin production. Giving chillies no fertiliser at all results in a weaker, stunted plant but chillies are hotter than they would be if fed. If you do feed, choose a specialist chilli feed, or use a tomato feed, to encourage the production of flowers, rather than leaves.

6. Reduce watering

Allowing plants to dry out completely between watering will also make the fruits hotter. The downside of this is that plants will be weakened and your harvest will be smaller.

Harvesting chillies

Chillies will be ready to pick from late summer. For the mildest flavour, pick chillies while they’re still green, leave them to mature for more heat.

Preparing and cooking chillies

Chillies add heat and flavour to curries, stir-fries and chilli con carne. Remove the seeds for less of a kick. Never touch your face or eyes while picking or preparing chillies.

Storing chillies

Chillies can be dried, prepared with garlic and oil to make a paste or pickled in vinegar. Store dried chillies in an airtight jar in a cool, dark place, or chop them roughly to make chilli flakes.

Growing chillies: problem solving

Blossom-end rot is a result of erratic watering.

Grey mould or botrytis can be a problem in a greenhouse. Remove any dead plant material promptly and ensure good ventiliation. Don't overcrowd plants.

Red spider mite can be a problem in a greenhouse – look out for webbing around the plant. It can be avoided by regular misting of the plant.

Whitefly can also be a problem indoors – use an organic soapy spray.

Turning down the heat

If you burn your mouth while eating chillies, try a spoonful of sugar or a glass of milk, rather than water.

Chilli varieties to try

Best chillies for a window sill

'Thai Hot' or 'Hot Thai' – tiny, very hot fruits on a compact plant

• Buy chilli 'Hot Thai' seeds from Suttons

'Pretty Purple' – small, round fruits that start off purple and ripen to yellow and orange, then red

• Buy chilli 'Pretty Purple' seeds from the South Devon Chilli Farm

'Malawi Birdseye' – a medium hot variety with small fruits that mature from green to red

• Buy chilli 'Malawi Birdseye' seeds from Nicky's Nursery

Best chillies for a patio or balcony

Chilli ‘Apache’ – these tough dwarf plants cope well outdoors. The pretty green fruits mature to red and are medium hot

• Buy chilli 'Apache' seeds from Dobies

Chilli 'Firecracker' – small, attractive fruits

• Buy chilli 'Firecracker' seeds from the South Devon Chilli Farm

Chilli 'Chilly Chilli' – attractive, ornamental fruits in a range of colours with hardly any heat

• Buy 'Chilly Chilli' seeds from the South Devon Chilli Farm

Mild chillies

Chilli 'Ancho Poblano' – great for stuffing and baking

• Buy chilli 'Ancho Poblano' seeds from the South Devon Chilli Farm

Chilli 'Cascabel' – round, almost black fruits that are often used dried

• Buy chilli 'Cascabel' seeds from Nicky's Nursery

Medium hot chillies

Chilli 'Hungarian Hot Wax' – long fruits that are good for stir fries. They are harvested yellow to keep the plant fruiting, but eventually ripen to orange

• Buy chilli 'Hungarian Hot Wax' seeds from Thompson & Morgan

Chilli ‘Joe’s Long Cayenne’ – the finger-like chillies, up to 25cm long, can be eaten green or red

• Buy chilli 'Joe's Long Cayenne' seeds from the South Devon Chilli Farm

Very hot chillies

Chilli 'Ring of Fire' or 'Ring O Fire' – long, pointed fruits that ripen from green to red

• Buy chilli 'Ring of Fire' seeds from Dobies

Chilli 'Bhut Jolokia' – extremely hot, wrinkly fruits - formerly considered to be the hottest chilli in the world

• Buy chilli 'Bhut Jolokia' seeds from Suttons

'Trinidad Scorpion' - extremely hot, wrinkly fruits

• Buy chilli 'Trinidad Scorpion' seeds from the South Devon Chilli Farm

'Carolina Reaper' – reputed to be one of hottest chillies available, at two million Scoville units.

• Buy chilli 'Carolina Reaper' seeds from Dobies