How hot can a marijuana grow room get when using CO2?

I know a marijuana grow room can get much hotter when it's using CO2 but hot can a marijuana flowering chamber get when it’s using CO2?

CO2 generally produces a rate of photosynthesis that is much faster than normal (as long as the cannabis plant receives light, water, and nutrients in sufficient amounts). The photosynthesis rate isn’t affected substantially by temperatures in the range of 65 to 90*F.

On the other hand, temperature does affect the metabolic rate of the marijuana plant, which is the rate at which the cell (and ultimately the plant) functions. Similar to cold-blooded animals, warmer temperatures produce faster life processes like conversion of food to energy and tissue growth. If the marijuana plants don’t have CO2, the best temperature range for cannabis is from the high 60s to the mid-70s. In this range, metabolism and plant growth are balanced adequately. When temperatures dip below 68*F, the rate of metabolism reduces, which increases the storage of sugar (vital for plant energy). But, the growth rate also slows.

At temperatures higher than the mid-70s, the metabolic rate increases, forcing the plant to use sugars on metabolism and less for creating tissue. Of course, this weakens the rate of tissue growth substantially.

If the air is enriched with CO2, sugar production increases dramatically, making the marijuana plant “thirstier” and “hungrier” for more water and nutrients. The plant could also use more light. Increased temperatures in the range of 80 to 85*F increase the plant’s metabolism, but it also increases the plant’s rate of tissue growth. Because the plant is producing more sugar, there is enough to go around for both tissue growth and metabolism. This ultimately results in faster tissue growth.



I can’t say exactly why in this moment, but I thought the upper range (or limit) was around 95 degrees F. Plant outside in most areas of the country would experience 90+ temps on regular basis during the course of a normal grow year. Unless you were at altitude. This will go on my very long list of things to find a solid reference for (not that I doubt you, as you have been, thus far, and incredibly reliable reference source). Off this topic, I finally ‘achieved’ a slight nute burn with foliar feeding, but only after two weeks of twice daily applications, and a step-wise increase in the strength of the fert. I ended at 100% package instructions for soil feeding, so I now know that if I keep it at, say, for example, 1/4 to 1/2 strength, I should be able to apply it indefinitely. This is a topic where there is mass disinformation on the web. Your’s was virtually the only voice saying it was possible daily. Darned if I don’t think you were correct…


The upper range may be 95 degrees; But, not necessarily the optimum temp.

I have always applied nutrients at full strength. Perhaps with C02 I would waiver, but I do not believe in 1/4 -1/2 strength nutrients solutions past seedling stage. If you vie the plants full strength nutes; You would not have to foliar feed as much.


 I was not so much foliar feeding that much to find an ultimate 'best practices' routine, but to see how much I might be able to do it.  For example, to bring sick girls back to health, and so forth.  I have always been, and shall always be, in a 'Boutique' situation, so I am not really looking for ways to do less work, but to utterly maximize health and wellness of my babies.  Also, (if memory serves) I think you said you don't do Auto's, which is what I was experiemneting on.  One nearly universal in every thread is not to overdo it with the nutes.  Now, this is most likely highlighted for beginner's, and I appreciate that (along with not over-watering, and learning about wet/dry cycle).  I must say, Robert's W.W. Autos love to be fed, expecially with the CO2.  I can't help but think that 'all cannabis is not all cannabis'.  There is tremendous individuality within all families of nature, be they dogs, cattle or plants.  If I could be in the with newbies, I would try and get them to 'listem' to the plants they have today.  Just really take time to look, think, ruminate.  Spend 'quality' time with them every day.  And stretch their mental wings beyond just our favorite plant, and learn about plants in general. as those principals help one understand the lowly Cannabis family.       
I appreciate you comment about the uppermost limit perhaps not being the optimal temp point.  Good thought.  Thanks!!