Greenhouses can become extremely hot on hot, sunny days in summer. While greenhouse crops like tomatoes, cucumbers, aubergines and melons thrive in heat, too much can put them under stress and cause tissue damage. Temperatures over 27°C can begin to cause damage - you might spot wilting, leaf scorch or dessicated young foliage. Very high temperatures can also cause poor pollination and damage to developing fruits.
There are three things that you need to do in the height of summer to keep your greenhouse cool: provide adequate ventilation, give shade from direct sunlight and damping down. It's also important to keep plants well watered.
To ensure the greenhouse is well ventilated, open all doors and vents early in the morning - this will help to keep the greenhouse cooler. Find out how to fit an automatic greenhouse vent.
Providing shade, in the form of netting, blinds or shade paint, will keep plants cool.
Damping down is simply pouring water onto the floor of the greenhouse. Do this first thing in the morning - as the water evaporates, it will create enough humidity throughout the day to prevent your plants from suffering heat stress. It also helps to reduce problems with red spider mite, which like a dry environment.
Here's how to damp down your greenhouse.