How Hot Is Too Hot?

So im holdin at 84 degrees F today, with my grow room pretty much in its final layout. I scored a rad remote sensor thermometer at home depot for like 15 bucks so now I don't have to crack the door to check temp! YAY! The 600 watt light is 19" away and in a vented hood. Soil Grow, no co2. Plants have been looking a little yellow especially near the bottoms, and are about a foot tall. Im pretty sure I overwatered them a little. Am I gonna b ok do you think? Please feel free to chime in

i get nervous when i get into the 80's.....id say anything over 85 is getting to be on the hot side..i try to keep mine at 79 ish

yellowing from the bottom up might be N def. if you haven't started adding nutes yet she might be hungry.

I wouldn't b worried about the temp 2 much
I have had my aircon fail and temps went up
2 around 108 and the plants were fine
Although ideally as stated by Dizzle Frost
The temps should b around the 80 mark give or take
Hope this helpsv
Good luck

I'm just a beginner, so take it for what it's worth, but from my research, 76-78 is the ideal temp, but many have the mistaken notion that anything over this is "too high." That just doesn't make sense to me because pot grows well in many places that get well over 78 degrees and often never gets that low at all. I struggled with heat at first, with temps soaring to 104 (documented too high as the leaves near the light started curling upward) and never dropping below 90. After several adjustments and additions, I have got my heat down to a high average of 80-82 with lows about 75, and my plants are thriving. Is that "ideal"? No, but it doesn't seem to be "too high" either. After struggling with 100+ heat, I am thrilled with it, and my plants seem to be as well.

Meant to add that I leveled at about 88 for awhile, and my plants still showed minor signs of heat stress, so what Dizzle says above about over 85 starting issues seems about right to me. My plants were still growing at that temp, but they definitely like the low 80s better.

Its not a question with a hard nailed answer,several things come into play & will change the equasition,humidity & air circulation both play a role in the question.

The higher the humidity level the less heat the plants can tollerate,air circulation as well where the better air flow you have through out the canopy the more heat they can tollerate.

Plants can be very happy & productive at 90 plus degrees as long as the humidity is low & the air flow is
causing a constant leaf flutter.

If it is uncomfortable to humans it is too hot.

The penalty for too high of temps isn't the death of the plant but the lack of density of the final product. I can have a 2 rooms FULL of buds, while they take up the same physical space. the plants grown under ideal conditions will yield a much denser and heavier final product. Giving you more usable product and a finer smoke.

Without supplemental co2 anything over 78 actually slows plant growth and can cause airy buds.

Thanks for the replies some interesting stuff I haven't thought of yet. Today the high got up to 88. I was thinking of a way to re-route my vent, carbon filter, and hood and I'm pretty sure I can make it a little more efficient. Also if I switch it onto 12/12 and run it at night that should help too. My wife said to me, its 88 degrees in Jamaica right?

Some plants really don't take well to the heat, but as long as you give them enough water they'll be ok. It's get over 100f in the summer here and I finish crops outdoors no problems.

Turned out to be nitro deficient. Bamfrivet called it. I thought no way thats it, but sure as shit the 4 i transplanted transformed after the first watering. Hopefully my nutes arrive today in the mail. also i threw em under 8 40w 4' flouros until i can improve my ventilation and the room is a cozy 74 degrees! thx dudes.

Glad you figured out the problem and it was an easy fix. Back to the heat issue, Im stuck with just being able to use fans inside a closet with not much fresh air flow so my temps are high. Pretty much stay steady around 89 during lights on and 84 or so during lights out. Again, not ideal, but they have been growing good and I'm happy with the results....

Those are pretty little plants...I'm sure with a little research I could figure out a good strain for high temps. I hope that doesn't turn out to be necessary though! Airflow is no joke, even with pretty good airflow heat can build up so quickly! My nutes arrive tomorrow so it will be interesting to take some before and after photos.

budhastalin said:

Thanks for the replies some interesting stuff I haven't thought of yet. Today the high got up to 88. I was thinking of a way to re-route my vent, carbon filter, and hood and I'm pretty sure I can make it a little more efficient. Also if I switch it onto 12/12 and run it at night that should help too. My wife said to me, its 88 degrees in Jamaica right?

Click to expand...

OK this seems like it would be too simple to be a good fix...but TRUST MEE it works real well.

Just angle a good fan towards your light towards your exhaust. HUGE help.. like 10degrees difference.

I'm curious why your having heat issues... is it cause your growing in a closed environment? no AC? How are you getting air in and out of your grow room? Where is cool fresh air coming from? anywhere? Air circulation is vital to gettin' good buds man. Whats the RH?

Hope alls good

Im in a small area 4.5' high, 5.5' wide, 9.5' long i have a passive intake through one area drawing air from another room. This is a stealth requirement. Although I am not breaking the law, its just for the security of my family and just for general discretion. I guess I could always draw air from outdoors, but indoors the air is always the same temp, and the humidity inside my home is always about the same so I don't mind a little higher heating and cooling bill in order to produce my own medicine! I have been able to get it down to 82 in midday with all the lights possible blazing, and I am happy with this for now. I was able to cut a square hole in my ceiling and mount mylight 70% out the top. This gives me about 1' more height for growing. I also have it airtight, so the cooled hood is cooled from the attic on top with a 235cfm 6'' fan (about $25 at Home Depot) keeping it as cold as possible. This also allows me to use my 170cfm fan and carbon filter to run on their own which is more efficient that using them attached to the cooled hood. Also, I moved the ballast into the attic above. All my plants are healthy and my 2 day old clones look happy. Great Idea about rigging a fan in that way. I will be able to do that easily, and will see if I can get a few more degrees!

It depends on the strain. I live in AZ. I'm indoor now, but last summer I had some thriving healthy AK47 that went all summer. Yes, you read that right. 110 in the worst part of late June. I had to get some tomato cloth and rely on indirect sunlight for about 4 - 6 weeks.

I'm sure the production suffered, but it was my first AK grow and I got over 20 OZ off 3 plants. They were started in May and harvested near Oct. 1st.

I was pretty happy with it. I'm sure I coulda got two or three times that amount of bud if conditions were optimal, but to answer your question....it can be done.

Another thing...they are constantly busting people here growing outdoors on National Forest land, and that's all hotter than a mofo too, but people do it successfully.

I was able to get about 3 degrees by angling a small fan from the light to the filter, now my lights are always off during the hottest part of the day, and its 11pm and currently 84 in there. I can live with it, things are looking very lush. Very slight upward curling on some of the plants' leaves edges but not on others, I think from the heat. I think I may try to construct a sort of collection hood to do a better job of collecting as much as possible of the warm air coming off from the light.
My air is pumped out at 170cfm and drawn in passively, thru a discreet area underneath my bathroom cupboards. Its a tight space, 230 cubic feet and 4.5 feet tall, and I have a more suitable area, but the stealth of this spot is unbelievable. I have no ac in the room, but it doesn't get to hot here and the GR is well insulated. I have a couple more tweaks to make....we'll see when I have time....about to go to 12/12 next week or so!

hope your buds turn out well!
with my set up mu flowers endure a high of at least 92f with no signs at all of heat issues. 600w hps 1.5' about from light.