How to damp down your greenhouse

BBC Gardeners' World Magazine

Published: Friday, 19 July 2019 at 4:03 pm

Find out why it's important to damp down your greenhouse on hot, sunny days, and how to do it.

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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.

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Here's how to damp down your greenhouse.

You Will Need

Watering can full of water

Step 1

When the weather forecast predicts hot and dry weather, pour water on the greenhouse floor early in the morning. This allows the water to slowly evaporate during the day, adding much-needed moisture to the air. You can repeat throughout the day if necessary.

Dampen the greenhouse floor, not the plants. Water dripping onto leaves encourages fungal disease, while water splashed onto fruit can ruin its appearance. Don't forget to keep your plants well watered, too.