What is the ideal temp in your opinion? It’s very hard to get my temp up without throwing everything else off.
From germination until early flower, a tent temperature of up to 85° will maximize growth of the plant. The purpose of the vegetative stage is to let the plant create a large infrastructure with a lot of branches, short internodal space, and a large number of small leaves. That "morphology" is created by giving a plant a lot of light, by using a light with at a good measure of blue in the spectrum, and, with the higher temperatures, the metabolic rate is high so it will be able to grow larger.
With temps in the low 70's, photosynthetic rates will be low. I've attached a graph from the Chandra paper and, while the paper has limitations, the net photosynthesis curve is helpful for this discussion.
Ambient CO2 is now 424ppm so the 500ppm mark on the X axis will have to do. At 20°C the rates of net Photosynthesis ("net P") is about the same as at 40° (104°F) with rates of 8µmol/m2/s. At 35/95, it's about 11, at 25/68 it's up to 13± and at 30/86, it's 18.
Roughly speaking, you will just about double the net P rate by raising the temperature from the low 70's to the mid 80's.
As an aside — one limitation of the study is that the data here are net P for individual leaves that were tested in a very small, environmentally controlled chamber (about the size of a shoe box). Growers who didn't read the paper thoroughly have taken this paper to claim that there's little reason to increase light levels above 500µmol "because the curve starts to roll off". That's simply not correct but, if you look across the world of cannabis sites, that passes for conventional wisdom and it's completely misleading.
My response to this paper was "What if I'm not harvesting net photosynthesis?". That's when I started looking for information about cannabis yields, ran across the Bugbee videos and research papers that have been published on that topic.)
In short, get your ambient temps up to the low to mid 80's if you can.
After the second week of flower, the plant stops building out its structure and the bud sites start to mature. At that point, temperatures above 78° will have a
significant negative impact on cannabanoids.
Some of the information above is basic plant biology. The "two weeks into flower" and the information about the impact of flower top temperatures above 78° was first published by Mitch Westmoreland about three years ago in a YT video on hemp. Westmoreland was doing the research for his PhD thesis and he shared this information, along with a huge amount of other data, in two videos that were released on You Tube early this year.
There's a lot of common information in the two videos but growers should watch at least one of them. They're easy to find, they're <1 hour long, and they are a gold mine of information.
