In a nutshell: sow seeds somewhere warm indoors in February or March, move the seedlings into bigger pots as they grow, keep them in the sunniest, warmest spot you have (a greenhouse, conservatory or sunny windowsill), and pick your chillies from July to October.
- DifficultyEasy, but slow to start
- Sow to harvestAbout 5–6 months
- WhereWarm and sunny: indoors or a greenhouse is best
- Pot sizeOne plant per 20–30cm pot
- Grows to30cm–1m, depending on the variety
The growing year
When to grow it
Next: sow under cover from January
- Sow under cover: January to April
- Plant out: May to June
- Harvest: July to October
Before you start
What you'll need
- Chilli seeds New to chillies? Start with a mild or medium variety, like Jalapeño.
- Small pots or a seed tray, and seed compost
- A heated propagator Optional, but chilli seeds need 20–25°C to come up, and a propagator keeps them steadily warm.
- Bigger pots, and multi-purpose compost To move them on as they grow, up to a final pot 20–30cm across.
- A warm, sunny spot A sunny windowsill, conservatory or greenhouse. They can go out on a sheltered, sunny patio in summer.
- Tomato feed A liquid feed for once the flowers appear.
- A self-watering planter Optional: makes summer watering much easier.
Step by step
How to grow chillies
February to March (January for very hot varieties)
Sow your seeds somewhere warm
Fill a small pot or seed tray with seed compost and water it. Scatter a few seeds on top, cover them with a thin layer of compost (about 5mm), and put a clear lid or a plastic bag over the pot to keep it moist.
Keep them warm, at 20–25°C. A heated propagator, or a warm windowsill above a radiator, works well.
Tip: Very hot chillies, like habaneros and Scotch bonnets, are slower to grow and ripen, so sow them from January.
You'll know it's working when tiny seedlings appear, usually in one to three weeks. Very hot varieties can take a month, so be patient.
When the seedlings have their second pair of leaves
Give each seedling its own pot
The first two leaves are the seed leaves; the next pair look like small chilli leaves. Once these appear, gently lift each seedling, holding it by a leaf (never the stem, which bruises easily), and plant it in its own small pot of multi-purpose compost. This is called pricking out.
Keep them in the brightest spot you have, and turn the pots every day so they grow straight.
You'll know it's working when the seedlings stand up straight, with dark green leaves.
March to May
Move them into bigger pots as they grow
When roots poke out of the bottom of the pot, move the plant into a pot a size or two bigger. Keep doing this until it’s in its final pot, 20–30cm across. This is called potting on.
Water when the top of the compost feels dry, and let the extra drain away: chillies hate sitting in wet compost.
Tip: Going up a pot size at a time, rather than straight into a big pot, stops the compost staying cold and wet around small roots.
You'll know it's working when the plants are bushy, and the roots fill each pot before you move them on.
Late May to June
Give them a warm home for the summer
Chillies need warmth and as much sun as they can get. A greenhouse, conservatory or sunny windowsill is ideal, and they can stay in their pots.
To grow them outside, wait until the frosts are over (usually June), harden them off for a week first, and put them in your sunniest, most sheltered spot, like a patio against a south-facing wall.
Tip: Taller varieties may need a short cane to hold them up when they’re heavy with fruit.
You'll know it's working when flowers appear: small white or purple stars.
June to September
Water, feed and help the flowers
Water regularly, letting the top of the compost dry a little in between. Once the flowers appear, give them a tomato feed every week.
Indoors, there are no bees to pollinate the flowers. On a sunny day, gently tap the stems or brush inside each flower with a small paintbrush, to help the chillies form.
Tip: Flowers that drop off usually mean the plant got too cold, too hot or too dry. Keep things steady, and open the greenhouse on hot days.
You'll know it's working when small chillies form where the flowers were.
July to October
Pick your chillies
Pick them green, or leave them to ripen to their final colour: red, yellow, orange, brown or even purple, depending on the variety. Ripe chillies are hotter and sweeter.
Cut them off with scissors, leaving a little stalk on. The more you pick, the more the plant makes.
Tip: Wear gloves to handle hot varieties, don’t touch your eyes, and wash your hands well afterwards.
You'll know it's working when the chillies are firm, glossy and full-sized.
Autumn
Use, freeze or dry them
Use them fresh, freeze them whole, or dry them: thread them on a string and hang them somewhere warm and dry.
Chilli plants can live for years. Bring yours indoors before the first frost, cut it back by about a third, keep it somewhere cool and bright, and water it just a little over winter. It will crop earlier next year.
Choosing what to grow
Which variety should I grow?
- Sweet and mildFrom no heat to a gentle warmth, like sweet peppers and Padron. Good if you're new to chillies or cooking for children.
- MediumA good kick, like a jalapeño. Easy to cook with, and quick to ripen: the best place to start.
- HotPlenty of fire for curries and chilli sauces, like Tabasco and Mirch Masala.
- Very hot and extremeHabaneros, Scotch bonnets and the hottest chillies in the world. They need more warmth and a longer season, so sow them early and grow them under cover.
Best for beginnersJalapeño M Chilli Pepper SeedsMedium heat: a good kick, and easy to cook with.
Hungarian Black Chilli Pepper SeedsMedium heat: a good kick, and easy to cook with.
Mirch Masala Chilli Pepper SeedsHot: plenty of fire for curries and sauces.
Havana Gold Chilli Pepper SeedsMedium heat: a good kick, and easy to cook with.
Orange Habanero Chilli SeedsVery hot: habanero heat. Wear gloves to handle them.Ready in about 100 days
Machu Picchu Chilli Pepper SeedsMedium heat: a good kick, and easy to cook with.
Padron Chilli Pepper SeedsMild: just a gentle warmth.
Jamaican Scotch Red Chilli Pepper SeedsVery hot: habanero heat. Wear gloves to handle them.
Aroma Habanero Chilli PeppersVery hot: habanero heat. Wear gloves to handle them.
Bhut Jolokia Chilli SeedsExtremely hot: among the hottest chillies in the world. Wear gloves to handle them.
Chocolate Habanero Chilli SeedsVery hot: habanero heat. Wear gloves to handle them.- See all 22 varietiesBrowse them all
Jargon buster
Words explained
- SowTo plant a seed.
- GerminateWhen a seed wakes up and starts to grow.
- PropagatorA covered tray, often heated, that keeps seeds warm and moist while they germinate.
- Seed leavesThe first two leaves a seedling makes. The ones after them are its true leaves.
- Pricking outMoving seedlings from where they were sown into pots of their own.
- Potting onMoving a plant into a bigger pot as it grows.
- Harden offGetting plants raised indoors used to outdoor weather, a little more each day.
- PollinationPollen moving from flower to flower, so fruit can form. Indoors, a gentle tap helps.
- Tomato feedA liquid fertiliser rich in potash, which helps plants flower and fruit.
- Scoville Heat Units (SHU)The scale chilli heat is measured on: a sweet pepper scores 0, a jalapeño a few thousand, the hottest chillies over a million.
- OverwinteringKeeping a plant alive indoors through the winter so it grows again next year.
If things go wrong
Problems and fixes
The seeds haven't come up
Why: Chilli seeds need steady warmth (20–25°C), and very hot varieties can take a month.
What to do: Move them somewhere warmer, like a propagator, keep the compost just moist, and give them time.
Seedlings are tall, thin and floppy
Why: Not enough light, so they're stretching towards it.
What to do: Move them to your brightest windowsill, turn them every day, and plant them a little deeper when you move them on.
Flowers drop off without making chillies
Why: Too cold, too hot, too dry, or not pollinated.
What to do: Water steadily, open the greenhouse on hot days, and tap the plants or brush the flowers to spread the pollen.
Tiny green or black insects under the leaves
Why: Greenfly (aphids), which love soft new growth.
What to do: Squash them, or wash them off with a spray of water. Check every few days, as they multiply quickly.
Fine webbing and pale, speckled leaves
Why: Red spider mite, which thrives in hot, dry air.
What to do: Mist the plants and wet the greenhouse floor on hot days, and pick off the worst leaves.
The chillies stay green
Why: Not enough warmth or sun to ripen them before autumn.
What to do: Green chillies are fine to eat. Next year, sow earlier (especially hot varieties) and give them your warmest spot.
Good to know
Questions people ask
Can I grow chillies on a windowsill?
Yes. A sunny south- or west-facing windowsill is ideal, especially for compact varieties. Turn the pots now and then so they grow evenly, and tap the flowers to help them set fruit.
Can chillies grow outside in the UK?
Yes, in a warm summer, in your sunniest, most sheltered spot, once the frosts are over. Mild and medium varieties do best outdoors; very hot ones are happier under cover.
Why aren't my chillies hot?
Heat depends mostly on the variety. Chillies also get hotter as they ripen, so leave them to change colour if you want more heat.
How hot is hot?
Chilli heat is measured in Scoville Heat Units (SHU). Our chilli heat guide explains the scale.
Can I keep my chilli plants for next year?
Yes. Bring them indoors before the first frost, cut them back by about a third, and keep them somewhere cool, bright and frost-free over winter, watering just a little. They’ll crop earlier next year.
More about growing chillies
This comprehensive guide covers everything you need to know to successfully grow chilli peppers in a UK greenhouse. Key topics include:
- Selecting the right chilli varieties based on heat level, plant size, and growing requirements
- Seed starting options, including using a propagation mat or sunny windowsill
- Maintaining ideal growing conditions like temperature, humidity, and lighting
- Preparing the soil and potting mixes for optimal plant health
- Tips for container growing and graduated transplanting
- Advanced automated watering systems to simplify irrigation
- Effective pest and disease management strategies
- Properly acclimating plants when transitioning outdoors
- Overwintering perennial chilli varieties for multi-year harvests
- Preserving your chilli pepper harvest through drying, pickling, and freezing
- UK-specific considerations like supplemental lighting and weather protection
With this detailed guidance, you’ll be able to cultivate an abundant, flavourful crop of homegrown chilli peppers in your UK greenhouse.
Selecting the Right Chilli Varieties
When choosing chilli varieties for your UK greenhouse, consider factors like heat level, plant size, and growing requirements. Popular Capsicum annuum varieties include jalapeño, cayenne, and bell peppers. Capsicum chinense types like habanero and ghost pepper offer extreme heat. Capsicum frutescens features the tabasco pepper, while Capsicum baccatum includes the fruity aji amarillo. For cooler climates, Capsicum pubescens varieties like rocoto are well-suited.
Understanding the Scoville Heat Unit (SHU) scale is crucial when selecting chillies. This measures pungency, with bell peppers at 0 SHU, jalapeños around 2,500-8,000 SHU, habaneros 100,000-350,000 SHU, and the ex-record-holding Carolina Reaper exceeding 1.5 million SHU. Choose varieties matching your preferred spice level.
Seed Starting Options
While using a heated propagation mat is ideal for maintaining the 27-32°C soil temperature required for optimal germination, you can also start chilli seeds on a sunny, south-facing windowsill if a mat isn’t available. Just be sure to monitor soil moisture carefully and provide supplemental lighting as needed. It’s best to start your chilli pepper seed off in late winter especially slow growing types like Capsicum chinense and most super hots as these require a very long growing season!
Ideal Growing Conditions
Chilli peppers thrive in warm, humid environments. Aim to maintain daytime temperatures between 18-25°C and night time lows of 15-17°C. Relative humidity levels should be 60-70% – use automated misting systems or strategic ventilation to achieve this.
Providing ample light is crucial. Chillies require at least 6 hours of direct sunlight per day, so site your greenhouse accordingly or supplement with high-output LED grow lights, especially during overcast weather and for seed starting.
Germination and Soil Preparation
For optimal germination, chilli seeds need consistently warm soil temperatures between 27-32°C. Use a heated propagation mat to maintain this range. Sow the seeds 0.5-1 cm deep in a sterile, well-draining seed starting mix, keeping the soil evenly moist but not waterlogged.
When preparing potting mixes, blend high-quality compost with perlite to create a light, airy medium that retains moisture without becoming dense or sodden. Amend with a balanced, slow-release organic fertiliser to nourish plants throughout the growing season.
Potting and Container Growing
Chilli plants thrive when grown in containers, as this allows you to control soil quality and moisture levels. Start seedlings in small pots or germination trays. Once they develop true leaves and outgrow the current tray or pot, transplant them into larger pots.
As the plants mature, gradually upsize the pots, moving to 1L and eventually 5L or larger containers. This staged repotting minimises transplant shock and encourages extensive, healthy root growth. Use premium potting mix and ensure excellent drainage.
Consistent, even soil moisture is crucial for chilli plants. Consider investing in automated watering systems designed specifically for container-grown chillies.
Watering
Regularly check the soil moisture by sticking your finger into the potting mix. Water deeply when the top inch feels dry, taking care not to waterlog the roots.
Advanced Watering Systems
- ChilliGrow System: Features a reservoir that maintains ideal moisture levels without risk of waterlogging.
- Quadgrow System: A self-watering setup that uses wicking action to keep the root zone hydrated.
- Autopots: Provide a continuous water supply, reducing labour and optimising efficiency.
These specialised systems take the guesswork out of watering, promoting optimal growth and abundant fruit production.
Pollination in Greenhouses
Since natural pollinators like bees are less frequent in greenhouses, you may need to hand-pollinate chilli flowers. Use a small, soft paintbrush to gently transfer pollen from the male stamens to the female stigmas, encouraging fruit set.
Pest and Disease Management
Common greenhouse pests that may target your chilli plants include aphids, slugs, snails, spider mites, and whiteflies. Use organic insecticidal soaps, neem oil, or introduce beneficial predators like ladybugs and lacewings to control infestations. Copper barriers and diatomaceous earth can deter slugs and snails.
For disease prevention, maintain good air circulation, use disease-resistant seed varieties, and avoid overhead watering, which can spread fungal spores. Watch for issues like powdery mildew, bacterial spot, and blossom end rot, treating promptly with organic fungicides if needed.
Acclimatising Plants Outdoors
When transitioning chilli plants from the greenhouse to the outdoor garden, take care to avoid shocking them with sudden changes in temperature, light, and wind exposure. Wait until all risk of frost has passed before moving plants outside, typically in late spring or early summer.
Gradually acclimate them by increasing their daily outdoor time over 7-10 days, starting with just a few hours and working up to full-day exposure. This incremental process allows the plants to toughen up and adjust to the new conditions.
Overwintering Chilli Peppers
Some chilli pepper varieties, particularly perennials like the rocoto (Capsicum pubescens), can be overwintered indoors with proper care. This allows you to enjoy the plant for multiple seasons. Reduce watering, provide bright light, and maintain temperatures around 15-18°C.
Harvesting Chilli Peppers
Depending on the variety, chilli peppers are typically ready to harvest 90-150 days after sowing. Look for visual cues like the desired colour (deep green for jalapeños, orange or red for habaneros) and firm, glossy skin.
Frequent harvesting, even removing individual peppers as they mature, encourages the plant to continue producing new fruit throughout the season. Snip the chilli’s from the plant using sharp, clean scissors, leaving a short stem attached. Avoid pulling or twisting, which can damage the plant. Alternatively you can allow all your chilli’s to ripen on the plant and harvest all at once at the end of the season.
Preserving Your Harvest
To enjoy your chilli peppers long after the growing season, consider drying, pickling, or freezing them. Dried chillies make excellent spice blends, while pickled or frozen peppers can add heat and flavour to countless dishes.
Tips
Remember that the UK’s shorter daylight hours, especially in winter, may require supplemental grow lighting to ensure your chilli plants receive enough light.
Perfecting Chilli Growing in a UK Greenhouse
By selecting the right chilli cultivars, providing ideal growing conditions, and managing pests and diseases, you can grow an abundant chillies in your greenhouse. With the guidance outlined in this comprehensive guide, you’ll be well on your way to spicing up your culinary adventures.
Ready to grow your own chillies?
From sweet to scorching, choose the heat that suits you and start sowing in late winter.
