VPD THREAD? Vapor Pressure Deficit information needed!!

Discussion in 'Advanced Marijuana Cultivation' started by Deathpack, Sep 14, 2017.


    Deathpack Member

    Thanks for the feedback... great info , will be sure to keep in mind! :D

    Huckster79 Well-Known Member

    I was a nube like you, i wanted more of a goal than just finish w live plant and a nug... i did all sorts of shit my first grow and learned lots by diving in deep... my best advice is triangulate off all the diff advice you get to make your own style, take nothing to extreme, do ny change slow, and ignore ppl's advice who tout their way as the only way..

    I think part of it is if your into botany youve grown something else before, many new growers have never grown a marigold so the simple get to finish w a smokable nug may be a solid goal for them...

    ruwtz Well-Known Member

    Not true. Ambient CO2 levels - typically 400ppm - in veg are more than sufficient.

    Elevated CO2 levels restricts stomata density https://www.sciencedaily.com/releases/2011/03/110303111624.htm

    Elevated CO2 levels constrain nitrogen acquisition
    Dr. Who and Roger A. Shrubber like this.

    Shugglet Well-Known Member

    The problem I have with the first study is that, if youre running CO2 at 1000-1500 ppm, you are 2-3x higher concentration levels than natural. Even if stomata density is reduced by ~30%(varies by plant) I would think the fact youre dealing with a 100-200% increase in co2 level would result in a net increase in available usable CO2 to the plant assuming no other bottlenecks. So in other words, while 400 probably is sufficient, elevated will increase the overall potential.

    Also a good reason why people running CO2 run higher temps, because they open the stomata.
    Dr. Who and fn217 like this.

    ruwtz Well-Known Member

    Interesting presumption, and worthy of some testing if you're up for it.

    Also, higher temps with CO2 are beneficial due to increased rapidity of metabolic processes, not necessarily opening stomata. In fact, under water stress, stomata will just as easily close at higher temps.
    fn217 and giglewigle like this.

    pop22 Well-Known Member

    I'd shoot myself before having all that crap in my growroom! If I wanting to work in a lab, I'd get a job in one! Growing at home isn't all about the almight gpw, its really about quality and the enjoyment of watching your plants develop.

    But to each his own, that's simply my feelings on it, so if you enjoy this style of growing, cool! I hope it brings you satisfaction! Myself, the simpler I can make my grow, the better.


    Jaybodankly Well-Known Member

    "If youre running CO2 at 1000-1500 ppm, you are 2-3x higher concentration levels than natural".

    My understanding is plants evolved under much higher levels of CO2 and heat for millions of years. Growing indoor is not natural. Creating better conditions for perfect growth than available outside is not natural. Creating an excellent growing environment is what we strive to do.

    whitebb2727 Well-Known Member

    I've never worried about vpd. I actually prefer my humidity lower than most recommend. 40% range.
    Instape likes this.

    ChaosHunter Well-Known Member


    Huckster79 Well-Known Member

    Id say the range given for late veg should be carried through the begining of flower, say 3 or 4 weeks even... lowers the stress of the flip as one less change, but i think really helps em grow in that rapid stage of development, once plant starts to be relatively fully formed and further growth will be more in a swelling and enlarging type of growth vs fresh new growrth then transition to drier and drier air... there is zero reason that rh needs to drop the night of the flip...but finish dry oh hell yea.. and a drop in temp to i prefer towards the end... i do my temp like i do my humidity dont change it day of flip... give it that warmth for the growing part of flower and cool temps w bone dry air... god i can almost taste the results of that just thinking about it... time to quit just thinking about it ;)

    Heber Member

    Vpd range u r shooting for is different thru different cycles. 1-4 for early veg, 4-8 late veg, 12-14 early/mid flower, 16-17 late flower here's a chart

    Attached Files:


    Heber Member

    High co2 levels actually temper the atomata openings , with the plant thinking it has enough co2 uptake, same reason plants grown under elevated co2 have lower stomata density... if plants are grown at atmospheric co2 thru veg (when leaves r forming)theoretically they will have normal stomata density... also, just my own theory I'm testing, reducing co2 to ambient half (600-700)of normal I run, for 7 days following defoliation (will keep posted on that)

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