I grow at a latitude of roughly 25°S (Pretoria, South Africa). Our climate is comparable to Texas or maybe Southern California. Growing in a greenhouse (6m x 4m for 24m²), but have blackout covers to control sunlight. One part of the greenhouse is for 18 hours of sun (I supplement it with a few hours of lights at night) and the other part gets only 12 hours of sun for the flowering plants.
Since September (beginning of spring for us) daily highs (lol, pun intended) have been around 30° Celsius OUTSIDE. Inside the greenhouse it goes to at least 5° to 10° hotter. Got vents, got fans moving air inside, even got vent fans for air-in and air-out.
Just purchased a 24000 BTU aircon that runs flat-out from 09:00 till 16:00 daily, and this helps, but only to the extent that it brings the temps close to outside temps. It NEVER gets it colder inside than outside. In desperation, I’ve put some 40% shade netting over the roof of the greenhouse (nothing on the sides). This does not seem to make any difference. Temps are currently hitting highs (sigh…I know…) of around 34° outside. These are quite extreme for us, as normally, at this time of year, our top temps would be around 30° at most. In Jan and Feb (our hottest months) temps may sometimes hit 34° or 36°.
PART 1 - Could I go as far as 60% shade netting, or even 80% netting, or will that take away too much UV that the plants need?
PART 2 - Since I have 40% up already, am I an idiot for wanting to simply add a 20% “OVER TOP OF THAT”, to get to 60%, or should I remove the 40% and simply replace it with 60% ?
For our American friends: 30° C is about 86° F, and 34° C is about 93° F.