Hartley Magazine

All the latest news, hints, tips and advice from our experts

How to deal with the summer heat in a greenhouse

There are so many considerations to bear in mind when growing plants in a controlled space such as a greenhouse – and this is particularly the case at this time of year.

While the summer is something of a boon for all kinds of gardeners, as there are a lot of activities to be getting on with, it is important to make sure that plants are not being starved of the water they need or dried out by the blisteringly hot summer sun.

Needless to say, the fact that glass panels magnify the heat mean that this goes double for anything that is being grown in a greenhouse.

While this may be the entire point of the space, it will still need to be dealt with.

You’ll know exactly when things need to be cooled down a little as it will probably start to get unbearable in there.

One of the most obvious things you can do is prop the doors open in the daytime.

They can also be left this way overnight if you feel comfortable doing so and it does not cool down too much when it gets dark.

If you are still unsure as to when it is really necessary to do this, then keep a thermometer in the greenhouse and start to open all the vents when the temperature gets a little past optimum.

greenhouse summer


A good rule of thumb is to aim for between 20 to 25 degrees C in the daytime, with a slightly lower target of 12 to 15 degrees C overnight.

Celebrity gardener Toby Buckland – who has published several books on the pastime and used to present television magazine show Gardeners’ World – underlined the importance of doing everything possible to conserve water in hot and dry conditions.

In an article for UK national newspaper the Daily Telegraph, he explained that there are several ways to go about doing this, adding that it can really help to ease the strain on plants that will already be struggling with the heat.

When it comes to greenhouse growing, he advised getting all of the watering that needs to be done out of the way early in the morning, before other tasks start to take up time.

He added that this is also a good opportunity to attend to plants that are particularly prone to rot, such as lavender, as this will give their foliage plenty of time to dry out in the sun.

The expert also noted that many gardening enthusiasts and professionals alike take advantage of flood and drain systems, in an effort to negate the risk of fungal infection:

“Basically, the whole greenhouse floor is a giant concrete bath that gets filled half-way up the sides of the pots and then the plug is pulled and the water drains away,” Mr Buckland explained.

“Based on exactly the same principle, I use a large plastic water trough to drench young plants that are easily washed out of their pots if watered with a hose,” he continued.

“A water bath doesn’t just rehydrate dry compost: as pots are lifted out of the drink, air – crucial for healthy rooting – gets drawn in through the surface of the compost, making for faster growth rates.”

Greenhouse pots