Growing peppers and chillies in a UK greenhouse

One guide, two related crops

Sweet peppers and chillies are both Capsicum crops that appreciate the extra warmth of a UK greenhouse. A single plan works for many of their needs: good light, a warm start, a sheltered growing position, steady water and careful ventilation. They are not identical, however. A compact chilli in a pot may ripen at a different rate from a large-fruited bell pepper, and some varieties become much taller than others. Read the packet's mature height, fruiting time and container advice before deciding how many plants the greenhouse can hold.

The RHS sweet-pepper guide and RHS chilli guide both describe greenhouse growing as especially useful in the UK. A warm greenhouse does not remove the need for light; starting seeds far too early can create oversized plants waiting for a still-cold final position.

Sow, pot on and move under glass

Sow in fresh seed compost at the warmth specified for the chosen variety. A controlled propagator can warm the small root zone without heating the whole greenhouse. Once seedlings emerge, give them strong light and suitable growing-on warmth rather than leaving them sealed under a humid lid. Pot on when roots and true leaves are ready, handling stems gently. The leggy-seedling guide helps if growth becomes stretched.

Do not confuse a sunny afternoon with a warm night. The RHS says sweet peppers can cope with a minimum night temperature around 12°C but grow better above 15°C, and positions planting in an unheated greenhouse around mid-May when conditions permit. A cold northern site may need later. Check several night minima in your own structure and use the seedling-moving guide for a gradual transfer.

Choose root space and supports

Peppers and chillies grow well in containers, but a pot that is too small dries quickly and may hold back a larger cultivar. Choose size from the seed supplier's guidance, provide drainage and leave room for air and harvest access. A greenhouse border can buffer moisture, but its soil requires long-term care; growbags versus borders compares the trade-offs. Add a cane or other support to taller, fruit-heavy plants while roots are still small. Tie stems loosely and revisit them as they thicken.

Group plants with similar water needs rather than assuming one drip setting serves everything in the house. Keep the growing medium evenly moist, not waterlogged. The RHS notes that dry conditions can cause sweet-pepper flower buds to fall; high greenhouse heat can also reduce fruiting. Ventilate and shade when needed, particularly during heatwaves. The overheating guide covers that response.

Feed, inspect and harvest

Container plants rely on nutrients in a finite growing medium. Follow the crop and fertiliser instructions, especially once flowers form; do not treat yellow leaves as proof of a single nutrient problem without checking roots, watering and pests. Inspect leaf undersides for aphids and other greenhouse visitors. Keep foliage accessible rather than packing pots into a still corner.

Harvesting green fruits can encourage more production, while leaving some to ripen develops the mature colour and, for many chillies, changes flavour and heat. Use the cultivar's description to judge the desired stage. Late in the season, reduced light slows ripening; a greenhouse extends the season but does not create summer conditions indefinitely. The UK greenhouse calendar helps plan when to clear plants and prepare for cool-season crops.