Quote Originally Posted by Weedhound
The temps of the leaf surface needs to remain under 80 degrees for maximum growth. Anything over 80 on the leaf surface will slow photosynthesis (sp?) down greatly costing you in plant health and growth.
I'm sorry, but can you show me the science on that?

That would suggest that a) there is one universal ideal temperature for photosynthesis that applies to EVERY plant and every strain of cannabis regardless of where it naturally grew in the world and 2) that tropical plants, if transplanted to a more temperate environment, would grow even more prolifically than they do in the jungle.

There are lots of reasons for limiting temperatures. Bugs and some other biological pests thrive as the temperature rises. Humidity becomes harder to maintain, and drier air causes plants to lose more moisture through transpiration. But photosynthesis being inhibited over 80F? Perhaps you should come and explain this to my vegetable garden. Better yet, tell the WEEDS around my garden that if it is over 80, they should grow more slowly.

I know I am new to the whole cannabis thing and all, but this smells strongly of something pulled from someone's nether regions and then passed around.

Science has shown that TREES (deciduous) in North America, regardless of latitude, prefer their leaves to be around 21C (69F) for the ideal photosynthesis and they will regulate their internal systems to try and keep them at that temperature. Mangroves, on the other hand, demand temperatures of 35C (95F) for photosynthesis. There is a great deal of variation depending on the prevailing conditions where the plant evolved. Those that grew best in the dominant temperature range over the years reproduced and thrived. Those that couldn't cope with those temperatures exited the gene pool, stage left.

Over the course of researching this stuff, I found a project had been done that found that 90-95F was the ideal temperature for maximum photosynthesis for cannabis. However, other factors play a part for the home grower making controlling a temp at 95F problematic, and the study was done under controlled laboratory conditions, not in a broom closet.

Yes, try to keep your temperatures down and under control. But the reasons for doing so have nothing to do with photosynthesis... insects reproduce more rapidly at higher temps, for starters. Many plant diseases can be exacerbated if the weather is warm. Parasitic infections and some moulds, and fungi often move at an almost uncontrollable rate when the temperature is high. And, it is a lot easier to get a spike from 95F to 115F before you notice it than to get one from 80F to 115F which will definitely make your plants unhappy.

But, considering most strains of this plant grow insanely fast as temperatures rise outdoors in tropical places (Jamaica averages 82F with daytime highs well above that, yet the weed seems to grow just fine), it isn't photosynthesis that is the problem. Afghanistan is known for producing high-grade indica pot - and summer temperatures run around 38C - that's 100F.

Come on - let's be real here. Show me a controlled-conditions study that demonstrates that warmer temperatures inhibit photosynthesis in cannabis of any strain. I'm serious, I would like to see this information.
PottyBear Reviewed by PottyBear on . Can't get below 93 deg.......... Heres my setup....... Closet - 48" H x 20"W x 20"D Single Waterfarm w/ 6" airstone 6 x 42 watt CFL Ducted 4" intake and exhaust mylar covered walls ( mylar wrapped around styrofoam panels) The room the closet is in is air conditioned down to 70 degrees I have my temp gauge located about 4" under the lights.......Is that the wrong place????? I can't get the temp in the box any lower than 93 degrees and thats with the room down to 70 and the fans constantly going. What am I doing Rating: 5