temperature variation - how much is too much?

hey guys, i'm doing an inside grow op under HPS lights, with fresh clones, and it was consistently staying too hot in my room (like around 88 degrees) and the littl'uns werent liking it, so i went thru the house, closed most of the a/c vents so now when i run the a/c (yes i know its november i shouldnt need a/c fucking global warming) but i discoverd now that the temp in my room drops from about 85 degrees to at the most extreme about 66 degrees. then when the a/c turns off the temp starts right back climbing uphill til it plateaus, and the a/c turns on, and teh cycle starts again. so i'm wondering, how much of a temperature change in what period of time is too extreme for the plants? is a 20 degree change in 15 minutes time 10 times a day too much?? obviously i wouldnt be asking if my clones looked 100% healthy...

the short answer is i don't know. but you were smart to listen to your plants and if they don't like the heat then cooling was necessary. i'd think a temperature swing from day to night could be 15-20 degrees difference without harm (again i'm not sure ... just surmising) but it seems like a lot of temperature swings throughout the day would be unnatural (but then again so is 24 hours of daylight)... hmmm good question think i'll stick with my orginal answer ... i don't know.. sorry

No that is not good for them. They are suppose to be around 75 with lights on and around 66 in dark. They can STAND higher and lower temps but its not good for them and especially not up and down like that every day. If it hits 88 one time and a few days later maybe drops low it might be alright but not every day. Put a fan on them man, or even 2. The ambient temp in the room might be hot but around the plants where the fans are it wont be 88. And you need to get an aircooled hood, that makes so much difference you wont believe it. If you cant do that put a fan upwards at the light to blow the heat away.

hey guys, thanks for ur replies. i happened to notice my neighbor had an oscillating fan in his garage tonite so i bummed it off of him and have set it up just like you said so it blows directly up at the light, blowing the heat up and away. my set up is in a bathroom so i've got the exhaust fan running 24/7 so im hoping by blowing the heat from the light directly upwards toward the ceiling that things will stay cooler.

I have a question, why is not ok for them not to get temps over 85d. It gets 90d + in Cal and drops under 70d at night. And I know they grow tons.
Any takers-

I dunno man. I guess its different for out door crops. All i know is over 95 will almost certainly kill them and below 55 will do the same. Its just how it is I have come to trust everything Jorge Cervantes says and ive read a few articles of his in high times and the back section where he answers questions and the temp question comes up ALOT.

I myself have found from experience that high heats will not kill your plants, nor will they harm them.

When you go and look at seedsbanks strains, you will notice that there are 3 different types, outdoor indoor and greenhouse, and this relates directly to what sort of temperatures you can grow them in.

Indoor strains like to have a higher heat and 75 deg isn't that, thats too cool for an indoor strain, that is better suited for an outdoor strain.

There isn't a set right or wrong on what the temps are best at, as for every strain its different dependant on where its native too.

75 is the ideal temp for indoor plants. Try to keep it around 75 when the lights are on and like 65 or so when the lights are off. Youll be a ok then dude. Good luck with everything.

Straight from this site's GrowFAQ

"A humidity and temperature gauge are essential in any growroom. Daytime conditions should be 70-80 degrees without co2, 80-90 degrees with co2 until the last two weeks when daytime temps should be kept between 70-80 and co2 can be reduced to adjust for the lower metabolism. Night temperatures should be kept above 60 degrees to prevent stress. It is preferrable during flowering to have a night temperature drop of 10-20 degrees to stimulate flowering hormones and reduce stem elongation.

I find that low humidity causes stress on plants. I recommend 50-60% humidity until the final 2 weeks of flowering. At this point, the humidity should be lowered as much as possible to encourage the plant to seal and protect itself with additional resin. (I am able to get the humidity to go as low as 31%) I have been able to frost things up considerably this way. The higher humidity levels prior to final ripening reduce salt levels within the plant tissue and encourage healthy, more lush growth."

I guess whoever writes the faq's for this site needs to learn a thing or two. Also, high heats will harm your plants. Anyone whose plants have been to close to lights or dont have a fan or something on them can tell you they will start to wilt very very fast if the temp is too high.

my opinion (not experience) would be that high heat (over 90 F) would be OK but a lot of severe (20-30 degrees) temperature swings caused by an AC kicking on and off probably would slow the plant growth down at least. but like i said - just an opinion not from experience or experiment.

I had MAJOR heat probs with my current grow. It got up to 100+degrees in the day and the plants seemed to adjust. I agree that the "75 degrees is ideal for indoor growing" is not always true. Every strain is different and originates from different parts of the world where the temperature varies considerably. I would say that 70-90 degrees is suitable for many strains. Cold temperatures will definitely kill your plants, but they seem to adjust to heat. My plants have been growing in 82-86 degree temps for the last two weeks and are loving it.

thanks for all the feedback guys. i think i have my situation better under control - i went to walmart last night at got a coolmist humidifier for $20 and a temp and humidity gauge for $6 (it also records the highest and lowest temp/humidity - very handy in this case to see how much the temps actually change). as soon as i got home i did an experiment by closing the door to the bathroom, with the humidifier on, and one fan blowing on my light and one on the plants. i can say the humidifier made a considerable difference in the temp inside the closed bathroom. the temp never got above 80 last night and never got below 74, relative humidity now is staying at 60%, up from like 41% before the humidifier.
hopefully my plants will really take off now! thanks again for all the feedback!

My plants haven't died they are doing good, there have been days when I go in and check the heat is 111d really hot of course I try to get the temps down and the norm is 90-95 from 8am to 5pm and down to 69d from 5pm to 8am. I'm saying this is not a good thing it just seams like these plants are doing ok. Maybe they would have been bigger.

Just curious.

ya i think heat that high would definitely stunt their growth.. hold old are they and how tall?