Greenhouse Growing

A greenhouse is a managed growing space, not a guarantee of warmth. Used well, it helps raise young plants, grow suitable summer crops and extend the harvest. Success depends on matching the crops to the light, temperature, water and attention available.

By Simon Adams · Updated 25 October 2026

Begin with a year-round plan

Decide whether the main purpose is raising seedlings, growing tender crops or producing leaves outside the main season. Allow working room, access to vents and enough space for mature plants. Plan where seedlings will go after potting on, rather than filling every bench at the first sowing.

Our greenhouse and polytunnel planning guide explains how to arrange protected and outdoor spaces together.

Know what your structure protects against

An unheated greenhouse reduces exposure to wind and rain, but can still become cold enough to damage tender plants. A sunny afternoon does not tell you how cold it was before dawn. Use a minimum–maximum thermometer near plant height, out of direct sunshine, and check temperatures in different positions.

Keep the distinction between the outdoor forecast and the conditions inside your greenhouse. Cold nights, draughts, shading and the type of structure affect the plants. Insulation may reduce heat loss but also reduces light. Choose protection for the actual crop, rather than wrapping the whole house automatically.

Ventilate before heat becomes a problem

Open appropriate vents and doors as conditions require and keep them accessible as plants grow. Automatic openers can help, but inspect their operation and remember that they do not water the crop or respond to every weather risk.

Ventilation alone may not prevent overheating. Add suitable shading during excessive heat, then reduce it when light levels fall. Check the effect on the plants: permanent heavy shade can limit growth. Use our heat and drought guide alongside regular observation.

Water the root zone consistently

Rain falling outside usually does not water protected beds or containers. Check their moisture separately. Small pots can dry before large containers or beds, so one watering routine will not suit everything.

Direct water to the growing medium and check that it reaches the rootball. Avoid letting plants alternate between severe dryness and saturation. Keep drainage working and adjust feeding to the crop and growing medium. The protected-crop watering guide covers the practical differences.

Use the seasons as a sequence

In spring, prioritise light and room for young plants. Choose summer crops that suit the conditions and varieties intended for protected cultivation. Our existing tomato, cucumber, pepper, aubergine and melon guides explain their individual needs.

For autumn and winter, plan hardy leaves early enough to establish before light and growth slow. Winter protection can preserve a crop for picking without producing rapid new growth. Use the harvest-extension guide to choose a realistic approach for your location.

Move plants outdoors gradually

Young plants need time to adjust to stronger light, wind and changing temperatures. Hardening off helps this adjustment but does not make tender crops frost-hardy. Use our planting-out guide to combine crop requirements, forecasts and garden observations before moving them permanently outside.

Keep the space easy to inspect

Leave room to check foliage, tie in growth and remove damaged material. Clear crop debris and clean accessible glazing to preserve light. Wash reachable surfaces gently, follow the glazing manufacturer’s care instructions and avoid leaning on glass or reaching across the roof. Inspect plants regularly before pests or disease become established.