Why peppers belong in a greenhouse

Peppers show exactly what a well-managed greenhouse can do: hold warmth, soften weather extremes and extend the cropping season.

Tomatoes are the classic protected crop, but peppers and chillies benefit just as much from cover. Large-fruited peppers need a long warm growing period that is not always dependable outdoors. In a greenhouse, young plants establish earlier, cooler nights are moderated and fruits can ripen for longer.

A greenhouse is not an automatic guarantee of success. Excessive heat can trigger flower drop, poor ventilation encourages pests, and frequent watering may cause root problems. Successful pepper growing is therefore about climate management, not protection alone.

This guide combines essential plant knowledge with a Maltese seasonal approach. It is for home growers using unheated or lightly heated greenhouses and explains how to guide peppers and chillies from seed to harvest.

Chapter 01

Choosing peppers and chillies for a Maltese greenhouse

For a home garden, it helps not to treat all peppers as one crop. Bell peppers produce large, thick-walled fruits and need considerable time to fully ripen. Pointed peppers, snack peppers and smaller sweet types are often quicker, making them well suited to compact greenhouses. Chillies range from mild jalapeños and shishitos to cayenne, habaneros and exceptionally hot specialist varieties.

In Malta, the ripening period still matters, but summer heat is often the greater challenge. A variety that performs well in a cooler Mediterranean climate may struggle in a very hot enclosed greenhouse. Read the seed packet for crop duration as well as final colour. Earlier varieties are often the safer choice in an unheated greenhouse.

Beginners can start with one reliable sweet variety and one robust chilli. This quickly reveals how a greenhouse performs for night temperature, summer heat, humidity and ripening speed. Where space allows, longer-season types can be added later.

German trials by the Bavarian State Institute for Viticulture and Horticulture show that pointed peppers can perform very well in an unheated polytunnel in Germany. This is useful as a German example: peppers do not require a heated commercial house, but they benefit greatly from protected warmth and a longer season.

Chapter 02

Sowing peppers and chillies: warmth first, light immediately after

Peppers are among the crops that need distinctly more warmth for germination than many vegetables. The Bavarian Garden Academy cites around 25 °C for pepper germination and recommends sowing in early March followed by bright growing conditions. For slow-ripening chillies or very early greenhouse crops, sowing can begin earlier if adequate supplementary light is available.

The crucial rule is to germinate warmly, then avoid growing seedlings on in warmth and darkness. Too much warmth with too little light produces long, soft seedlings. After emergence, plants need as much light as possible and slightly less heat than during germination. Good young plants are compact, sturdy and dark green.

Disturb roots as little as possible when pricking out and potting on. Peppers react more sensitively to rough root damage than tomatoes, for example. Once roots have filled the pot, move plants on promptly so growth does not stall.

Planting in an unheated greenhouse should follow the actual night temperature inside, rather than a fixed calendar date. In Malta, autumn planting and late-winter establishment can suit many sites, while hot summer conditions call for caution. A min-max thermometer in the greenhouse is more reliable than any general date.

Peppers enjoy warmth, but too much reduces fruit set. A practical range is around 21–27 °C by day and 16–21 °C at night. Growth slows markedly below about 15 °C. Very hot days and warm nights can also cause flowers to fall and small fruits to be shed.

A Maltese greenhouse has two contrasting seasons. In winter and early spring, stored warmth is a major advantage. In late spring and summer, the same structure can become a heat trap. Open roof vents and doors early, not only after plants wilt. During prolonged heat, shading can be helpful.

Local differences matter. A sheltered urban garden or south-facing coastal site may need much stronger summer cooling than an exposed garden with regular airflow. In warmer locations, preventing overheating is usually more important than extending the season; in cooler, windier places, stored warmth remains valuable.

The LWG highlights variety choice, irrigation and climate management for heat-loving fruit vegetables under cover. For home growers, that means measuring temperature, managing ventilation actively and not assuming that ‘more heat’ automatically means ‘more peppers’.

Chapter 04

Soil, feeding and water: peppers like consistency

Peppers need a loose, humus-rich, well-drained root zone. Waterlogging is particularly troublesome because warm greenhouse air can tempt growers to water again when the lower root zone is still wet. Incorporate organic matter in beds; use a stable, airy vegetable compost in containers.

Overfeeding is a frequent mistake. Too much nitrogen creates large, dark-green plants with plenty of leaf growth but not necessarily many fruits. From flowering onwards, nutrition should be balanced with adequate potassium. In pots, regular moderate feeds are safer than occasional heavy doses.

Water should remain consistently available. Sharp changes between drought and saturated compost encourage flower drop and blossom-end rot. Drip irrigation is especially practical in a greenhouse because leaves stay dry and root-zone moisture is easier to manage.

Water demand changes sharply through the Maltese year. Containers can dry quickly during hot, windy spells, while the same amount of water may be excessive in winter. Check the root zone and adjust watering to weather, pot size and plant growth.

Chapter 06

Spacing, support and companion crops in the greenhouse

Planting too closely is one of the most common greenhouse mistakes. Peppers need light into the canopy and enough moving air. Bell peppers often become wider and heavier than expected, while bushy chillies can need substantial room. Wider spacing reduces pest pressure and makes harvesting easier.

Heavy fruits make support worthwhile. Simple canes, strings or small cages prevent side shoots from breaking under the weight. Large-fruited pepper varieties particularly benefit from early support, before plants begin to lean.

Peppers and tomatoes can share a greenhouse because their temperature and light requirements are similar. However, both are solanaceous crops and share several pests and diseases. Tall tomatoes must not shade the peppers.

Peppers can also be grown with cucumbers, but humidity management becomes harder. Cucumbers quickly make a dense, moist canopy. Think of the greenhouse in zones: give peppers the bright, airy area and cucumbers the position where higher humidity causes fewer problems.

Blossom-end rot is not a classic fungal disease. It is usually a physiological problem linked to calcium supply and, above all, uneven water uptake. Large fruits are more vulnerable. Consistent watering and healthy roots matter more than rushed calcium applications without finding the cause.

Yellow leaves can have many causes: waterlogging, nutrient shortage, cold roots, root damage or pests. Never feed solely in response to leaf colour. Check moisture, temperature and root condition first.

Aphids, whitefly, thrips and spider mites are typical greenhouse problems. Early checks of shoot tips and leaf undersides are vital. Thrips deserve particular attention because they can transmit virus diseases.

Heat damage is also often misread. Sunscald on fruits appears as a pale, dry patch on exposed sides. Good leaf cover, timely ventilation and light shading during extreme heat reduce the risk.

Chapter 08

Harvesting, colour development and overwintering

Green bell peppers are usually red, yellow or orange fruits that have not fully ripened. Picking green reduces the burden on the plant and can bring more follow-on fruits. Waiting for full colour generally produces sweeter, more aromatic fruit, but needs more time.

Depending on the variety, chillies can be harvested green or fully ripe. Many develop more intense flavour and sometimes greater heat at their final colour. Regular picking encourages further flowering and keeps production going longer.

In a Maltese greenhouse, harvests can often continue through the cooler months, provided plants remain healthy. As nights cool, water use drops. Water less, allow chosen fruits to ripen and remove diseased plants early.

Peppers are biologically perennial. Favourite chillies can be overwintered frost-free with sufficient light and serious pest control. Starting again in the next suitable season is often simpler for bell peppers, but overwintering can be rewarding for special chilli varieties.