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Discussion in 'Newbie Central' started by CrazyJohn91, Sep 15, 2009.


    CrazyJohn91 Member

    What is the coldest temperature a marijuana plant can be in?

    LUDACRIS New Member

    Room temperature should stay between 72 - 85 degrees Fahrenheit. Yes, I could say 78 is ideal, but if you can retain your room temperature in this range, you should be fine. Sometimes, being exact will drive you nuts, and sometimes you NEED to be exact. Your humidity is good if 45 - 65 percent can be maintained in your vegetative grow room. Oh, and yes, your room can get to 60-65 degrees Fahrenheit at night (lights out) without any problems.

    TEMPERATURE - Cannabis Growing Guide

    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, 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 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 50s will cause mild shock and 40s 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.

    Bbcchance likes this.

    CrazyJohn91 Member

    Alright thx just wanted to make sure that i shouldn't have it get under 60 degrees Farenheit. I saw this article today or something that said the lowest temp a marijuana plant could be in was 30 degrees faranheit.

    LUDACRIS New Member

    below 50 can kill.
    the correct temps are essential for optimum growth and plant health and if you are way of your plants required temps you can end up with all sorts of problems.
    nute lockup is just one of the effects that come with incorrect temps.


    CrazyJohn91 Member

    Alright thx + rep

    cacafruty Member

    I disagree with all of you guys (the ones saying the below 50 degr. can kill plants) Remember, weed is weed! and as such it adapts. The original strain originated in one of the coldest regions (at night anyway) in the world, the Hindus valley!

    The growth is affected for sure with lower temps but it will take something close to the actual freezing point to kill the plant. I have a few growing outdoor here in N.E and there's been already a few nights in the mid/low 40's. The plants seem to be ok and they're certainly not dead (that they growing or not internally is another matter)

    Just my two cents.

    Nugglet Well-Known Member

    Welcome to RIU btw. I see ur a stranger so ill just throw it out that Luda is never wrong haha.. But i see ur point. Yes ur plants will still grow in that temp but it does cause problems and stunts them.
    But once it frosts ur past the growing point. Yank those bitchs out. Unless it was a freak frost and its not happening everynight.

    Cheers Nug

    CrazyJohn91 Member

    O so your saying i dont have to worry about the temp at night unless it is freezing????

    Nugglet Well-Known Member

    no... none of us said that.. Cold temps will start to hurt ur plant aftertime. But it will definitly stunt it and cause nute lock like luda said. Idea temps is what u want.. if u cant control that start to makeshift ideas on how to give ur plant those conditions. Be crafty.. ur growing marijuana, u should be able to jimmyrig something

    CrazyJohn91 Member

    Well now i have them inside but you see the winter is coming and i live in middle of nowhere in a loghome and the electic likes to go on and off here so idk why else i could use as a light for them with no electric.
    diamond doggy

    diamond doggy New Member

    damn, im growing outdoors and the weather sucks.. way below 50 degrees at night and 60's during the day.. with lots of rain.. im fucted, i have a 5foot tall plant, not showing any signs of over watering or anything.. think she'll make it?
    Jimbo Dixie Dean

    Jimbo Dixie Dean Member

    Hi I am aware that this thread is well and truly 'dead and buried' but was just curious to know if you can remember if the plant survived and if you actuallly got any smokeable bud off it?
    warren kirk

    warren kirk Active Member

    I know this old, But Dude, 33, and below kills, 40below stunds. U can run cold temps all time. Look outside, watch mother nature.
    Kevin McCallister

    Kevin McCallister Member

    Mid 60's is as low as I've ever pushed em. When. They get really cold they sometimes change color. Cold Temps can cause your plant to be purple or yellow or I've even had blue spots. Something about chlorophyll and cold Temps that interacts. No lower than 60 is what I'd recommend
    warren kirk

    warren kirk Active Member

    That's it in a nut shell

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