What are ideal temperatures for marijuana plants that are flowering and/or in vegetative growth?
For the most part, the best growth rates are going to come when the temperature ranges from 70 to 74*F during the light period, with a drop of around 10 degrees (to no lower than the high 50’s) during the dark period. Photosynthesis slows down significantly if the temperatures are lower during the light period. A temperature rise correlates to stable photosynthesis rates, but increased metabolic rates—an action that causes the marijuana plant to use much of the sugar produced during photosynthesis.
When CO2 enrichment is used and light intensity is optimized, the marijuana plants perform better at higher temperatures during the day (mid-80s F) and during the dark period (mid-70s F). The higher temperature is frequently useful for cannabis growers, since the heat from lights and other equipment must be managed.
I saw a thing wherein a commercial grower explained that the 75-85 degree ‘standard’ came about due to the extra heat under the HID or HPS lamps (canopy temps). He said that with LED’s (he was standing in a warehouse-sized room of them) the ambient temperature ought to be 85-95, and the plant will transpire more, and that that is the optimal temperature range for transpiration of the Cannabis plant. More transpiration = more movement of water/nutes from the roots up, more potential for growth.
I’ll tell you what gripe’s my rear-end (thanks for asking…) - the lack of scholarly, peer-reviewed journal papers of any kind or stripe on Cannabis. 50 years of the War on Drugs, and nobody was even doing research? (I KNOW this is because no one could risk saying they had even possessed weed in the 80’s-90’s, but it is still aggravating).