Growing chillies is one of the most rewarding things you do in a greenhouse. There are thousands of varieties, ranging from mild and sweet to ferociously hot, in a whole rainbow of colours, and almost all of them are happy in a pot. Originally from hot climates, chilli plants love warmth and sun, which is exactly why a greenhouse suits them so well: it gives them the long, warm season they need to crop generously in the UK.
Chillies are tender plants that need heat and a good run of time to ripen, so most UK gardeners start them under cover. The good news is that they are a relatively low-maintenance crop, and even a windowsill or a small greenhouse is enough to get going. They also make handsome plants in their own right, with glossy leaves and bright, dangling fruit through late summer and autumn.
Growing chillies in the greenhouse
A greenhouse is the ideal home for chillies in the UK. It gives them the warmth and the long season they need, shelters them from wind and cold nights, and keeps the fruit ripening well into autumn. You raise the plants from seed early in the year, then grow them in pots in the warmest, brightest part of the house. If you are short on space, even a compact patio greenhouse will happily house a few plants, and a greenhouse heater makes the early weeks far more reliable when nights are still cold.
Growing chillies from seed
Growing chillies from seed is the cheapest route and gives you by far the widest choice of varieties. The key is to start early enough. Sow chilli seeds any time from January to early April. The slower, hotter varieties such as Scotch Bonnet and Habanero benefit from the earliest sowings to give them the longest possible season to mature, while milder, quicker types like Jalapeno and Cayenne are fine sown a little later.
Fill small pots or seed trays with good-quality, peat-free seed compost with a loose, open structure. Sow the seeds on the surface and cover them with just a thin layer of compost or vermiculite, so they sit only just below the surface. Water gently and label each pot, which really matters if you are sowing several types of differing heat. Chilli seeds need real warmth to germinate, so aim for around 18 to 25C, ideally in a heated propagator. Germination can take a couple of weeks, so be patient.
Keep the pots somewhere bright and warm while they grow. Greenhouse shelving or a seedrack lifts your seedlings off a cold floor and keeps them close to the light, which young chilli plants need plenty of to avoid growing leggy. Once each seedling has its first pair of true leaves, prick it out and pot it on into its own small pot, handling it by the leaves rather than the delicate stem.
As the plants grow, keep potting them on so the roots never sit cramped. Stand the young plants on the staging in the sunniest spot you have. Chilli seedlings are happiest with steady warmth and good light, so a cold, dim corner will only slow them down.
Growing chillies from young plants
If you missed the early sowing window, or simply want a head start, you can buy young chilli plants in spring from garden centres and online specialists. This is the easy route: someone else has done the fiddly germination for you, and you can have established plants growing on within days. The choice of varieties is narrower than with seed, but you will still find the popular favourites such as Jalapeno, Cayenne and a few hotter types.
Pot young plants on into 20 to 25cm pots of good general-purpose compost as soon as you get them home, and stand them in the warmest, brightest part of the greenhouse. From here, they are cared for in exactly the same way as seed-raised plants. Give them a few days to settle, keep them warm, and they will soon start to put on growth.
Care and how to harvest
Once your plants are growing in their final pots, the routine is straightforward. Water regularly so the compost stays evenly moist but not wet, which in a warm greenhouse can mean a good soak around twice a week in the height of summer. Give each plant a supporting cane early on, before the roots fill the pot, and tie the main stem in loosely as it grows so it does not flop or snap under the weight of fruit. When a plant reaches around 20cm tall, pinch out the growing tip to encourage bushier growth and more side shoots, which means more flowers and a heavier crop.
Chilli flowers are self-pollinating, so each flower can set fruit on its own.
Top Tip: Under glass, where there are fewer insects moving around, you can give pollination a helping hand by gently tapping the plants or brushing the open flowers with a soft paintbrush to move the pollen around.
Once the first fruits have set, feed weekly with a high-potassium tomato feed (like Tomorite) to fuel a generous crop. Misting the leaves with water now and then keeps the air a little humid and helps deter red spider mite.
Chillies can be picked green or left on the plant to ripen to red, orange, yellow or even purple, depending on the variety. Green fruits tend to taste fresher and slightly less hot, while fully ripe ones are sweeter and usually carry more heat. The heat itself comes from a compound called capsaicin, and the level varies enormously between varieties, which is what the Scoville scale measures.
Harvest runs from around July through to October under glass. Picking regularly encourages the plant to keep producing, so do not let fruit sit too long. Wear gloves and snip each fruit off with a short stalk using scissors or a sharp knife, and keep your hands away from your eyes while you work.
Chilli companion plants
Chillies do well alongside a few good neighbours. Basil is the classic partner: it enjoys the same warm, sunny conditions, is said to help deter aphids and whitefly, and is no bad thing to have to hand in the kitchen either. Marigolds (Tagetes) are another reliable choice, widely planted among greenhouse crops to draw in hoverflies and other beneficial insects that prey on aphids.
Tomatoes make natural companions too, since they want the same warmth, light and feeding regime, which makes it easy to grow the two side by side. If you already grow tomatoes or cucumbers under glass, chillies will slot neatly into the same greenhouse routine. Other herbs such as coriander and chives are happy nearby as well. As a general rule, give each plant enough space and air movement so leaves dry quickly and pests find it harder to take hold.
Chilli pests and problems and how to avoid them
Chillies are generally trouble-free, especially if you keep the plants healthy and the air moving, but a handful of problems are worth knowing about. Most can be managed without reaching for chemicals.
Aphids and greenfly are the most common nuisance, clustering on soft new growth and the undersides of leaves and weakening the plant. Whitefly can be a problem under glass too, rising in little clouds when you disturb the plants. Rub small numbers off by hand or wash them away with a jet of water, and encourage natural predators such as ladybirds and hoverflies, which is exactly what companion marigolds help to do. A sticky yellow trap helps keep whitefly numbers in check.
Red spider mite thrives in the hot, dry air of a greenhouse, causing fine pale mottling on the leaves and, in bad cases, faint webbing. The simplest defence is to keep humidity up by misting the plants and damping down the floor on hot days, as the mites dislike moist air. Good ventilation and not letting the house overheat both help.
Blossom drop, where flowers fall before they set fruit, is usually a sign of stress: an over-hot greenhouse, or compost that has been allowed to dry out and then flooded. Steady watering and a little shade or ventilation in the hottest part of summer keep the plants comfortable and the flowers setting.
Damping off can fell seedlings overnight, causing them to keel over at the base. It is brought on by sowing too thickly in cold, wet, airless conditions. Use fresh compost, sow thinly, keep things warm and bright, and water carefully from below to avoid it. More broadly, overwatering is the single most common way to lose a chilli plant, so always let the surface dry slightly between waterings and never leave pots standing in water.
Cooking with chillies
Half the fun of growing chillies is using them. Fresh chillies bring instant heat to stir-fries, curries and salsas, and a single home-grown one often has far more character than anything from a shop. For a taste of what is possible, this bashed cucumbers with green chillies recipe from chef Gill Meller on the Rhino blog pairs your chillies with home-grown cucumbers for a quick, fresh side dish.
A glut is easy to deal with, as chillies preserve beautifully. To dry them, pick fruit with a short length of stalk, tie them into bunches and hang them somewhere warm and airy, such as the eaves of the greenhouse or a sunny kitchen, where they will dry over a few weeks and look striking while they do it. They also freeze very well: simply bag them up whole and add them straight to your cooking, grated or chopped from frozen. Beyond that, home-grown chillies make excellent hot sauces, chilli jams and infused oils.
If you fancy more ideas, the Rhino recipes from the garden collection is full of seasonal dishes from Gill Meller, with new ones added regularly.
Growing chillies really is a satisfying way to use a greenhouse. Give them an early start, plenty of warmth and light, steady watering and a good feed once they fruit, and you will be picking your own fiery, colourful crop right through late summer and autumn. For more seasonal growing advice, our greenhouse knowledge hub is always a good place to start.