Max High Temp Cannibas Still Grows

[dddaver]

I read a long time ago it was 87F. My cab is running at 87F now. So I Googled it .Most returns say high temps should never exceed 85F. But some also said it was dependent on airflow and if CO2 is being added. And even some that said their temperatures in their greenhouses often exceed mid 90s and plants still flourish (relating to that airflow increase I imagine).

I can only say my plants still grow well at 87F. I have a small 4" Vortex (had that sucker for 12 years) sucking in fresh air from outside, but not sure of cfm. Enough it seems though.

So, I think it really depends. But does anyone know for sure of the definitive max temp where cannabis sativa L. growth stops?

 

[starke]

Lighting choice makes a difference also. My girls are much happier under full spectrum LEDs at about 84-86 degrees. Several others on here have mentioned running higher temps with LEDs compared to MH/CMH etc.

 

[Phaeton]

All things are relative. The maximum temperature for growth is probably quite a bit higher than expected, well into the 100's F.
Efficiency of growth is also a benchmark.
86 F gives the combination of high efficiency energy conversion and rapid growth. This falls off as the temperature rises.
As the temperature go down the fall off is slower, with growth not stopping until less than 60 F.

Anecdotes: During summer a warm spell had daytime temps running 105 F and night temps 89 F.
This went on for almost two weeks. All the plants lived and produced on time. Yields were a tad bit light, but not a major loss.
Winter day temperatures run 80 F and nights get down to 49 F. This goes on for almost six weeks. All the plants live and harvests are on time. Buds are smaller but not a lot smaller.

The target is the 86 F that has tested out best in laboratory conditions. The temp sensor for that is 2" above the top bud directly in the beam of the grow light.
Sensors for ambient air and container temps are also used, but canopy temps are the important numbers.

Too cool is better than too hot, the harvests between 80 and 86 are pretty much identical. The harvests between 86 and 92 are more significantly different.

 

[Bahseado]

Each plant from a seed has its optimal temperature of growing and a maximum tolerance of temperature, for hot and cold. Considering a single plant, it will even be different through its stages of life, and will depend on its health, nutrients available, and something very important: the humidity. Together, with some other factors, they manage to open or close the stomata, which are pores found on the leaves that facilitate gas exchange, playing a crucial role in temperature maintenance. Cannabis is a strong plant, worldwide spread so it had to adapt itself to a lot of conditions, so they can handle both high and low temperatures. I've personally grown plants under 100F (not all the time, just in the hottest part of the day) and everything went fine. Outdoor grows around here easily hit over this temp and also work fine.

An important thing about high temps are the terpenes profile. Higher temps may degrade or stop its production, thus changing the smell and flavour of a plant, and even the potency when smoked, as now we know some compounds like these have a modulatory effect over cannabinoids. A lot of growers prefer to grow and do selections in lower temps because plants could express more hidden flavours. But that might not be true for every single plant, as one more adapted to heat might have a better terpene expression in higher temps. As Phaeton said, everything is relative!

 

[Easy7]

It's all about leaf and root temp.

LED lightwaves are cool, unless they put out UV. Air temp and temp you feel from light itself is different. All HID and CMH puts out UV, even HPS.

 

[Starmstr]

It's well over 105 for 2/3 months outdoor. During this time plants continue to grow.

 

[MJPassion]

I read a long time ago it was 87F. My cab is running at 87F now. So I Googled it .Most returns say high temps should never exceed 85F. But some also said it was dependent on airflow and if CO2 is being added. And even some that said their temperatures in their greenhouses often exceed mid 90s and plants still flourish (relating to that airflow increase I imagine).

I can only say my plants still grow well at 87F. I have a small 4" Vortex (had that sucker for 12 years) sucking in fresh air from outside, but not sure of cfm. Enough it seems though.

So, I think it really depends. But does anyone know for sure of the definitive max temp where cannabis sativa L. growth stops?

I’m not so sure your going to get a definite answer.

That said, I’ve seen plants in environments (outdoors) that exceeded 100F & not be bothered.

Indoors you will have to add CO2 & lots of water & incorporate huge air movements while keeping an eye on RH so the enviro doesn’t become desicated.

 

[brown_thumb]

I'm having issues as low as upper 80's F but it's only when associated with very low humidity and bright full sun. The plants can't transpire quickly enough so the leaves dry to crisps.

 

[are you awake]

while living in the desert, our summers were always 90-120F. My plants thrived, grew 8-10ft (id have to tie them down so they wouldnt grow over the brick wall!).

IMO some strains do better than others. I spent the first 2 years there just breeding/selecting for the most heat tolerant plant. Skunks, big bud, and headband did really well. thats what i ended up crossing (plus threw in some locally grown bag-seed to start with)

 

[El Timbo]

I think it also depends on the age of the plant.

 

[Creeperpark]

As the temperature increases, transpiration will increase due to a higher concentration of sunlight and warm air. The amount of water the plant has is the governing factor in heat toleration. What allows a plant to tolerate higher temps is water transpiration through the stomata. Plants can only thrive during high temps when they have enough water to transpire the gases from the roots to the top of the plant. On hot days a large plant can transpire a few gallons a day or more. Without a lot of water, the plant will suffer from heat damage. Heat tolerance is governed by water intake and transpiration. .

 

[Creeperpark]

The Sativa growing regions can get hot and they seem to tolerate the highest temps the best. I have found that the best way for me to grow Indica dominate strains is to wait until after Summer Solstice before planting them outdoors. Vietnam can get as high as 110F , 43C and if you planted a short-cool-season Indica there it probably would fail. Genetics do play an important role in heat resistance and can make or break the grow.