On a hot, sunny day a greenhouse can reach temperatures that scorch leaves, halt fruit set and stress plants badly. Cooling it is about shedding incoming heat and moving hot air out — using several methods together. Here’s how, in order of impact.
1. Maximise ventilation
Open every vent and the door, and rely on automatic vent openers so it vents while you’re out. Hot air escapes through roof vents while cooler air enters low down. Many greenhouses are under-vented — adding a louvre helps. See ventilation.
2. Shade to cut the heat at source
Shade cloth or shade paint reduces the solar energy entering, so the greenhouse simply gains less heat — often the difference between coping and cooking in high summer. It also protects plants from scorch.
3. Damping down
Wetting the floor and benches (“damping down”) on hot mornings cools the air as the water evaporates and raises humidity, which many plants appreciate in heat. Repeat as it dries; avoid soaking foliage late in the day.
4. Fans and air movement
An extraction or circulation fan boosts cooling when natural ventilation isn’t enough, especially in still, hot weather.
5. Water wisely
Water in the morning so plants are turgid before the heat, and again in the evening if needed; well-watered plants withstand heat far better. See watering greenhouse plants.
Quick questions
What is the fastest way to cool a greenhouse? Open all vents and the door and get air moving with a fan; shading and damping down reduce the heat load so ventilation can keep up.
