# How hot is to hot ?



## cantoke (Dec 26, 2009)

I have heard and read that anything higher than 80 F is to hot that cause's sugar in the plant to turn to alcohol and that in turn screws up respiration and production of THC. But some people seem to get by with 82-84 F and produce some awesome shit, so they say. I guess some strains are just better adapted to heat than others. Thats what i would guess but a friend says it doesnt matter that outdoors that is true but indoors since the plant is receiving more hours of light and nutes etc. it is being forced to grow at an accelerated rate it makes it more sensitive to stress of all kinds including heat thus the need for cooler temperatures. Anyone know anything about this and are there certain strains that can tolerate more heat indoors than others. Opinions, comments, advice greatly appreciated im sure there are other people wondering the same thing. Could some of the wise growers out there educate me and other new growers. Thanks


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## thelastpirate (Dec 27, 2009)

cantoke said:


> I have heard and read that anything higher than 80 F is to hot that cause's sugar in the plant to turn to alcohol and that in turn screws up respiration and production of THC. But some people seem to get by with 82-84 F and produce some awesome shit, so they say. I guess some strains are just better adapted to heat than others. Thats what i would guess but a friend says it doesnt matter that outdoors that is true but indoors since the plant is receiving more hours of light and nutes etc. it is being forced to grow at an accelerated rate it makes it more sensitive to stress of all kinds including heat thus the need for cooler temperatures. Anyone know anything about this and are there certain strains that can tolerate more heat indoors than others. Opinions, comments, advice greatly appreciated im sure there are other people wondering the same thing. Could some of the wise growers out there educate me and other new growers. Thanks


 
Have you "heard or read" anything on whether or not the the sugars in the plant can _actually turn to alcohol_ from heat? Is that possible? And if _thats_ possible, then could the plant survive the alcohol?

Or do you just read shit and take it as gospel? Bone up on your biology there, cuz the science behind that one is flawed, Sparky.

Yeah, there are strains out there that handle higher temps than others. Introducing CO2 is most effective at around 90 deg F if I'm not mistaken.


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## Bigol'Bong (Dec 27, 2009)

keep in mind marijuana is native to places on the equator where it can become even hotter then that and the plant has been around for thousands of years. I was growing plants in 98-101 degree temps for 3-4 months and they were fine


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## Kushinator (Dec 27, 2009)

/


thelastpirate said:


> Have you "heard or read" anything on whether or not the the sugars in the plant can _actually turn to alcohol_ from heat? Is that possible? And if _thats_ possible, then could the plant survive the alcohol?
> 
> Or do you just read shit and take it as gospel? Bone up on your biology there, cuz the science behind that one is flawed, Sparky.
> 
> Yeah, there are strains out there that handle higher temps than others. Introducing CO2 is most effective at around 90 deg F if I'm not mistaken.


 Wow...so much love here. 

Ed Rosenthal says this:


*TEMPERATURE*

Proper temperature is one highly variable factor. Most books state optimum grow temperature to be 70-80 degrees, but many list extenuating circumstances that allow temperatures to go higher. Assuming genetics is not a factor, marijuana plants seem to be able to absorb more light at higher temps, perhaps up to 90 degrees. High light and CO2 levels could make this go as high as 95 degrees for increased marijuana growth speed.* An optimum of 95 degrees is new data that assumes very-high light, CO2 enrichment of 1500 ppm and good regular venting to keep humidity down. It is not clear if these temperature will reduce potency in flowers. It may be a good idea to reduce temperatures once flowering has started, to preserve potency, even if it does reduce growth speed. But higher temperatures will make plants grow vegetatively much faster, by exciting the plants metabolism, assuming the required levels of CO2 and light are available, and humidity is not allowed to get too high. 
With normal levels of CO2, in a well vented space, 90 degrees would seem to be the absolute max, while 85 may be closer to optimum, even with a great deal of light available. Do not let the room temperature get over 35 C (95 F) as this hurts growth. Optimal temperature is 27-30 C (80-86 F) if you have strong light with no CO2 enrichment. Less than 21 C (70 F) is too cold for good growth. 
Low temperatures at night are OK down to about 60 degrees outdoors, then start to effect the growth in a big way. Mid 50s will cause mild shock and 40s will kill your plants with repeated exposure. Keep your plants warm, especially the roots. Elevate pots if you think the ground is sucking the heat out of the roots. This is an issue if you have a slab or other type of cold floor. 
As temperature goes up, so does the ability of the air to hold water, thus reducing humidity, so a higher average temperature should reduce risk of fungus. 
Contrary to many reports, high humidity is not good for plants except during germination and rooting. Lower humidity levels help the plant transpire CO2 and reduce risk of molds during flowering. 
Studies indicate the potency of buds goes down as the temperature goes up, so it is important to see that the plants do not get too hot during flowering cycles. ? D. Gold: CO2, Temperature and Humidity, 1991 Edited by E. Rosenthal.



I simply typed "proper temperatures for Marijuana and CO2" in my Google Search, and Voila!

It would appear that as temps go up, THC production and efficiency seem to drop, at least according to Ed Rosenthal, who is pretty bright.

You CAN go up to 95 degrees, however, Ed feels that between 80 and 86 degrees is best (that is how I had understood it when I set my rooms up...they run at 79 to 84 degrees all the time during lights on) as above 86 degrees can see a decrease in THC content and effectiveness. Above 95 degrees at any stage and growth itself suffers. If you read carefully, you will note that he ONLY lets temps get above 86 degrees in the growth stage, never in flowering.

So...it would appear that your advice may work, thelastpirate, however,, that little bit about having higher THC levels if you don't go above 86 degrees is pretty important, imo. And no flowering plant should ever get above 85 degrees, with or without CO2, imo, as well.


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## jackdirty (Dec 27, 2009)

my rule of thumb is be below 85 if u aint rocking co2


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## MacGuyver4.2.0 (Dec 27, 2009)

jackdirty said:


> my rule of thumb is be below 85 if u aint rocking co2


 
Another major factor is your temps...88 degrees farenheit is too hot, sorry! 

Plants exchange water vapor and gases thru pores called Stomates or Stomata. When it gets too hot these pores close up and the plant starts the slow march towards death. 

Here is what happens when it gets too hot:

Temperatures
Plants have optimum growing conditions across the range of temperatures from 70°F to 85°F. Hot temperatures can injure and kill living plant systems. The thermal death threshold varies depending upon the duration of hot temperatures, the absolute highest temperature reached, tissue age, thermal mass, water content of tissue, and ability of the plant to make adjustments to temperature changes. 



Internal changes within the plant as heat loading effects increase: 

Decrease in photosynthesis (Ps) and increase in respiration (Rs).
Closing down of Ps (turn-over point for Ps and Rs = 95°F).
Closed stomates stop CO2 capture and food production.
Major slowing of transpiration (loss of heat dissipation, increase of internal temperature, and transportation / absorption problems).
Increasing cell membrane leakage.
Continued physical water loss and dehydration.
Cell division and expansion inhibited, and growth regulation disrupted.
Plant starvation through rapid use of food reserves, inefficient food use, increased photo-respiration, and inability to call on reserves when and where needed.
Toxins generated (cell membrane releases and respiration problems) and deficiencies of elements and metabolites occur.
Membrane integrity loss and protein breakdown.
Local cell death, tissue lesions, and tissue death.
What I have found personally-

-Larger pots are critical not only for proper growth but also cooling.

-Best temps for flower are not higher than 77 degrees if you can (75 ideal) a bit higher for properly CO2 enriched rooms.

-Proper amount of FRESH air from outside. Normal CO2 levels in outdoor air is approx 387 ppm average.


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## Kushinator (Dec 27, 2009)

jackdirty said:


> my rule of thumb is be below 85 if u aint rocking co2


I should probably note that I grow in sealed rooms, and run CO2 from tanks the entire cycle from veg to flower.

I average between 4.75 and .5.25 ounces of dry bud per plant in 4.5 X 8 X 8 foot rooms (2) with two 600 watt HPS bulbs over two 3' X 6" grow trays (7 plants in each room, and two 600 watt HPS per room). 

I use a drip hydroponic set up with a 30 gal res,and feedings every three hours when the lights are on. I use the Lucas Formula just as published, with no additives to it. Just the two part mix.

Sorry I didn't give that data the first time.


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## jackdirty (Dec 27, 2009)

well idk i run 4 1000w in a semisealed room with co2 my temps never get over 85 and my plant love it i grow in 5 gall tall pots filled with sunshine mix#4, but yes if your running hydro i would suggest keeping the room cooler so your water does get to hot in your res. less work on your water chiller if you run one.. i also run a ac too.. if your plants seem like there stress over 88 degrees trysilica blast i think botanicare carries it idkif i speltthat right,i foliar feed in veg and it seems like it makes my plants more sturdy and more resisant to temp change


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## surphin (Dec 27, 2009)

Bigol'Bong said:


> keep in mind marijuana is native to places on the equator where it can become even hotter then that and the plant has been around for thousands of years. I was growing plants in 98-101 degree temps for 3-4 months and they were fine


Very true, it is called weed after all. It can grow in just about any condition, anywhere. As to how that may effect potency and yield is different question. 

When you were growing at 98 - 101, was that all the time or was that just at the peak of the day?


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## diddydady (Dec 27, 2009)

I know that when I put my room over 90 my plants would dry out so fast. I just make sure that if the room gets really hot keep cool water on the roots. In soil, make sure its getting plenty of water. hydro, dont let that water get over 80, keep it even cooler the water will have more oxygen.


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## cantoke (Dec 28, 2009)

thelastpirate said:


> Have you "heard or read" anything on whether or not the the sugars in the plant can _actually turn to alcohol_ from heat? Is that possible? And if _thats_ possible, then could the plant survive the alcohol?
> 
> Or do you just read shit and take it as gospel? Bone up on your biology there, cuz the science behind that one is flawed, Sparky.
> 
> Yeah, there are strains out there that handle higher temps than others. Introducing CO2 is most effective at around 90 deg F if I'm not mistaken.


I read i listen i try to learn and am open to new ideas unlike some people and have you read or can you quote or prove that heat doesnt cause other things like stress to turn sugars ito alcohol the person who told me this has been growing for 20 years and grows killer shit so excuse me sparky for just trying to sort out fact from fiction thanks for the love


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## Kriegs (Dec 28, 2009)

I just use common sense, as much respect as I have for people who really try to dig deep like Rosenthal. For me that means letting the temp be what it will be, and as long as it's below 90F, I'm happy and the plants look happy. Preferably, I like a ceiling of 85F, but if we have an unseasonably warm winter day that drives the "lights-on" temp up for awhile, I figure that mimics natural conditions, and MJ is well-prepared to handle it, maybe even enjoy it. At night, it drops to what I set my HVAC for -- 65F.

A lot of growers promote a 10-20F drop from lights on to lights off. That's what I get with no effort on my part. 

I realize though, that everyone's setup varies in terms of size, location, airflow, season etc... When I first started, I had a 400W in a closet and temps hit 95F regularly. I don't think they "liked" it, but the plants turned out a lot of great bud, and that's the whole point for me, as much as I love perfection for its own sake.


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## Ronjohn7779 (Dec 28, 2009)

Ideally you don't want to go over the 75 to 80 degree range (80 getting kind of on the high side). Some people have somehow grown indoors at the 90 degree range just fine. I'm sure it all depends on genetics. Certain genetics will do better at hotter temps than others.


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## Thc-ch-ef (Nov 6, 2020)

Is 30’c and 40rh too high for flowering


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## CannabisErecticus (Nov 6, 2020)

Kriegs said:


> I just use common sense, as much respect as I have for people who really try to dig deep like Rosenthal. For me that means letting the temp be what it will be, and as long as it's below 90F, I'm happy and the plants look happy. Preferably, I like a ceiling of 85F, but if we have an unseasonably warm winter day that drives the "lights-on" temp up for awhile, I figure that mimics natural conditions, and MJ is well-prepared to handle it, maybe even enjoy it. At night, it drops to what I set my HVAC for -- 65F.
> 
> A lot of growers promote a 10-20F drop from lights on to lights off. That's what I get with no effort on my part.
> 
> I realize though, that everyone's setup varies in terms of size, location, airflow, season etc... When I first started, I had a 400W in a closet and temps hit 95F regularly. I don't think they "liked" it, but the plants turned out a lot of great bud, and that's the whole point for me, as much as I love perfection for its own sake.


I like rosenthal but he does some extremely unnecessary things when it comes to growing, have you ever seen his seedling process, for the love of god it’s the most unnecessary system I’ve ever seen, 30 steps and a laboratory are required to pop seeds in his opinion...


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## MintyDreadlocks (Nov 6, 2020)

This thread is 11 years old people. LMAO


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## Thc-ch-ef (Nov 6, 2020)

So? Do you have an answer


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## Loz32145 (Nov 6, 2020)

Rule of thumb.. if its too hot for you it's too hot for your plant. I seem to do fine with 28°c-31°c (about 85°f)


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## CannabisErecticus (Nov 6, 2020)

Loz32145 said:


> Rule of thumb.. if its too hot for you it's too hot for your plant. I seem to do fine with 28°c-31°c (about 85°f)


Couldn’t have said it better


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## Doug Dawson (Nov 6, 2020)

MintyDreadlocks said:


> This thread is 11 years old people. LMAO


LOL, back from the dead.


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## Thc-ch-ef (Nov 6, 2020)

Loz32145 said:


> Rule of thumb.. if its too hot for you it's too hot for your plant. I seem to do fine with 28°c-31°c (about 85°f)


First 2 pics don’t seem to like 
Last 3 are ok 
Exhaust fan/carbon filter is on high, I have a 10” household occelating fan on med. but don’t know if should turn to high?. It’s pretty breezy in there now on med.


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