Start early, but provide enough light
Chillies and sweet peppers are tender, long-season crops. Sow indoors from January to March if you can provide warmth and good light; without a bright windowsill or grow light, a later sowing may produce sturdier plants. Use fresh seed compost and sow about 0.5 cm deep. A propagator around 21–25°C helps germination, which may take one to three weeks or longer for some varieties.
As soon as seedlings emerge, remove the lid and move them into the brightest position available. Keep the compost lightly moist, not saturated. Pot on when roots fill the module, handling the plant by a leaf. Avoid leaving seedlings in a cold greenhouse overnight.
Choose the warmest growing position
A greenhouse or polytunnel gives the most reliable UK crop. Compact varieties can grow in a sunny indoor window, while outdoor growing is most successful in a warm, sheltered spot such as a south-facing patio. Harden plants off gradually over one to two weeks. Move them outdoors only when frost risk has passed and nights are reliably mild; cold checks delay flowering and ripening.
Use a container with drainage holes and enough volume to hold moisture through hot weather. In a bed, space plants according to their mature size, commonly about 40–50 cm apart. Add a cane for taller varieties and keep the greenhouse ventilated in hot weather. Very high temperatures can reduce fruit set, so shade lightly if the structure overheats.
Keep water and feeding even
Water at the base when the surface begins to dry, aiming for even moisture rather than cycles of drought and flooding. Small pots dry quickly. Once flowers and fruits are developing, feed according to a suitable tomato or pepper fertiliser label; do not overfeed nitrogen, which encourages leafy growth at the expense of fruit.
Flowers usually self-pollinate, but a gentle movement of plants or tapping flower stems can help under cover when airflow is low. Inspect leaf undersides for aphids, whitefly and spider mites. Remove pests by hand or use a targeted control that is safe for edible plants and pollinators, following its label.
Ripen and harvest before autumn cold
Sweet peppers can be picked green once full sized or left to colour, depending on the variety and flavour you want. Chillies are usually hotter and more aromatic when fully ripe, but heat varies by cultivar and growing conditions. Cut fruits with scissors rather than pulling on brittle branches.
From late summer, remove flowers and tiny fruits unlikely to mature before cold weather. Keep plants warm and bright for as long as possible. Potted chilli plants can sometimes be overwintered in a frost-free, bright place, but reduce watering and inspect for pests; sweet peppers are less reliably kept for another season.