Peter wrote
Hi, having just purchased an automatic vent openner for my greenhouse,
what is a suitable temperature to set it open at, I'm growing tomatoes
and melons (hopefully). And in a similar vein, is shading for the
greenhouse a necessity.
Many thanks in advance.

Get yourself a good Max/Min thermometer and use that to set when the vent
opens/shuts.
From what I've read at 80°F tomatoes stop growing so try to keep it under
that if possible.

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Regards
Bob Hobden