Greenhouse Temperatures ?

**Capsid** · 20-05-2009, 12:00 AM

There is only one optimum temperature

but the upper and lower limits are 40C and 0C for the plants you intend to grow. In summer then the lower limit is not a concern, but you will need to ventilate and/or shade the greenhouse to prevent excessive heat.

**teakdesk** · 20-05-2009, 12:11 AM

Unless you intend to heat your greenhouse you can only control the upper temperatures.

If you haven't already fitted them, a pair of auto-vents will be a boon in summer (esp. if we have the hot summer being forecast). You can also fit one to a louvre window if you have one.

In summer keeping the greenhouse cool will be the problem.

I set my auto-vents so that they have just closed when the evening temperatures have dropped to around 18 to 20 degC to keep heat in over-night. The opening temperature sets itself this way but they will fully open as soon as we get some sun.

My max-min thermometer in my un-heated greenhouse hasn't dropped below 9 degC over-night for the last three weeks (which, although a bit cold for toms etc will not harm them).

I also have shading up in hot weather to keep it cool (not needed at the moment!!!!!!!!

).

Edit: just one last point - keep your thermometer shaded so that you are measuring air temperature and not the direct rays of the sun!!

**SarzWix** · 20-05-2009, 12:36 AM

Aubergines tend to sulk at anything lower than 15�c, and the others don't like it much below 10�c. Below 5�c will cause problems, so keep an eye on the weather forecast

**lynda66** · 20-05-2009, 01:08 AM

you're possibly a bit late for aubergines ... unless we have a sunny summer and autumn .... but worth a go cos you never know what might happen

apparently they need a long growing season

**Madasafish** · 20-05-2009, 06:45 AM

My tomatoes tolerate 5C overnight - which is what we are getting even now. In earlier months I use a small paraffin heater.
And insulation.

In a hot summer, glass shielding ...or 40C +! and wilting plants..

**Caro** · 20-05-2009, 01:40 PM

Thanks to everyone for your advice and info. I have automatic openers on my vents and if it starts to look as if Scotland really will get a summer this year, I'll look into shading!

Caro

**Alice** · 20-05-2009, 09:48 PM

Welcome to the Vine Caro.

In an ideal world tomatoes like it between 18 - 25 degrees but will be OK with anything above 5 overnight. Mine are living outside.

Aubergines seem to like it as hot as they can get it and don't do well in cold conditions.

The peppers should get along in the same temps as the tomatoes.

Good luck with the project.

**Galileo** · 21-05-2009, 02:35 AM

The book "The Greenhouse Expert" lists above 30C as into the danger zone. As Alice said tomatoes like it in the 18C - 25C range.

18C by day and 16C at night seems to be the commercial standard. Tomatoes like lots of light within this temperature range. Its tough to achieve this in an amateur greenhouse but you will still get lots of great tomatoes outside of this range. After all we are not after perfection

Decide on what is your main crop. Mine are tomatoes so I try and keep the greenhouse temperature to suite them and the other plants Cucumbers Peppers Aubergines etc make do.

However keeping the greenhouse temperature below 30C is tough on a hot sunny day even with all the vents and the door fully open.

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