how cold is too cold?

just curious, anyone out there with some info on how cold is too cold in the grow room at night..

the plant should live if it doesnt frost, however cold will slow growth. cold can also help induce flowering faster and possibly influence sex.

i run 2 tents at the same time, my veg tent for 18/6 and my flower tent 12/12..today i split my ac into 2 separate ducts as too cool down both tents, which means having cold air flowing into the flower tent for 3hrs before lights on and 3hrs after lights out, shouldn't drop below 60 if i do that.. just wondering what to expect..if its safe, bad idea, or just any advice regarding this.. thanks!

bad idea to go too much below sixty it will stunt growth depending on the strain. some take cold better, but for the most part i go for upper sixties at night and upper 70's in the day

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

Mine is getting in the upper 50s and my plants seem to love it..

all great info, thanks! im still messing with the temps, right now the ac is set at 61 but the tent was already mid nineties so i needed extra low temp to cool it down quickly.. im guessing when its finalize the ac will be set to 65, meaning it shouldnt get much cooler than 60-65 for those few hrs before and after the lights..sounds like it wont be a problem!

Mines around 60 so I dont sweat it yet,it wont be long Ill have to throw a little heat in there...peace

We still got plants outside that are enclosed in a plastic house (ghetto). Everything but them is super iced in the morning (every morning) an these are our top budz!

I have been in the 70's & 60's and my kids seem to be ok