VPD THREAD? Vapor Pressure Deficit information needed!!

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


    Deathpack Member


    I am a beginner level grower, and am taking on my first rodeo :-D hahaha...after months of observation, years of connoisseuring and lifetime love for all things botany. I've decided to take on a few methods that most growers do not practice... I've been reading up on transpiration, and have been looking for ways to keep my VEG room on point when it comes to how much moisture is in the air.. i've added some humidifiers to the rooms , and am constantly checking temps/RH to make sure i don't step foot into a danger zone... ANY TIPS?

    MAIN VEG - 75* F
    51% RH

    ROOM 1 - 80* F
    53 % RH

    Note: I transplanted a few plants from veg (at about 2 - 2 1/2 feet tall) into 15 gallon smart pots.. I plan to veg them for another 2-4 weeks..

    Any help or tips would be greatly appreciated...

    ~ death :joint:

    chemphlegm likes this.

    chemphlegm Well-Known Member

    over thinking it man. relax

    humidifier, dehumidifier, ac, air scrubber, moving air, fresh air/c02 and heat controlled=success
    ruwtz likes this.

    Deathpack Member

    i overthink things lol...good info, thanks
    chemphlegm likes this.

    Sureshot2 Well-Known Member

    For those temps your RH seems a bit low to me. I run at 65% RH with air temps between 75-77f and even that I think is a bit on the low side for proper VPD.

    ruwtz Well-Known Member

    You probably don't wanna hear this, first rodeo and all. And I get it cos i've been there, but honestly it is sound advice.

    You can easily tie yourself in knots chasing VPD in the name of perfection. I know I did.

    Some might disagree but in my opinion the solid science behind much of VPD research isn't so applicable to our beloved plant here, and fighting to hit the 'zone' found on some chart could even hurt your girls. You might easily find those humidity numbers relative to temperature are just way too high and much more suit leafy veggies and fruiting plants.

    I run similar temps/humidity as you and my garden never misses a beat. I don't sweat minor swings and plants are always happy and vigorous. You'll find people running all kinds of temps/humidity variables with great success, proof if it is needed that there is no absolute in VPD in relation to cannabis.

    My advice would be to put your good mind to more critical things like light intensity, air flow, watering regimen and plant training.
    Last edited: Sep 14, 2017

    Deathpack Member

    Great response thank you so much, if you ever come across one of my posts again please feel free to comment, as I am a big believer in constructive criticism as long as it is positive.

    Craigson and pop22 like this.

    GreenSanta Well-Known Member

    also some small scale growers might end up with mold in all corners of their houses trying to chase VPD, ... indoor grows are not like greenhouses. I am happy at 45-55% RH regardless of temps.
    Tyleb173rd likes this.

    Deathpack Member

    oh that i was sure of haha, but it was for a room that is comfortably housing 225 gallons of soil in an insulated super clean, super controlled environment.. I realized i was stressing this issue too much, currently vegging with 2 of the 9 lights on, as i'm looking to install mini splits this weekend... was just freaking out a little haha ... but my room is currently at 81* F and has an RH of 55%.. thanks for all the great tips!!! your replies are greatly appreciated :D

    ruwtz Well-Known Member

    Lets check in on that 'super controlled' part when you have everything turned on full blast and crammed witg vigorously flowering plants 8-)

    Good luck with it all!
    Heil Tweetler and Tyleb173rd like this.

    zypheruk Well-Known Member

    I personally think all this vpd shit etc is something 90% of home growers growing in tents will never nail, way to many variables, now if your growing in a sealed room then yes you should be able to nail it easy enough.
    I may be totally wrong and talking shit that my cf filter ain't filtering..

    RM3 Well-Known Member

    VPD is a waste of time, as the charts floatin around are not about cannabis (as has been stated) and even if they were it would require replicating the test environment to duplicate

    The best way to get cannabis in the zone is to adjust for a heat index 4 points above ambient
    Dr. Who and zypheruk like this.
    Carolina Dream'n

    Carolina Dream'n Well-Known Member

    I run my veg room at 86 degrees 75% humidity, 1300 ppm co2.
    Flower room starts at that and slowly starts ramping down to 77 degrees 50%, 800 ppm co2 by the last week.

    VPD only works if you are supplementing co2 in my opinion. The results are amazing once it's dialed in. 1-2 inches of growth a day in veg.
    SoCal Calyx, Jaybodankly and zypheruk like this.

    Jaybodankly Well-Known Member

    You are putting in the right effort to control your grow environment. The more control you have the better grower you will be. I recommend a data logger. I use a Sensorpush $50. There are others. Maybe be better ones. Havent looked in awhile. They are temp/hum sensors that send text to your phone if it falls out side the hi/low settings. The app provides a nice graph chart hour, day, week, month, year.
    SoCal Calyx likes this.

    Deathpack Member

    Awesome tip! Thank you so much for your kind words..... your help is appreciated.. :D If i could like posts id hit the thumbs up haha

    Deathpack Member

    Setting up my co2 tanks along with the AC units this weekend hopefully... working with what i have to keep the girls as pretty as they can be, i will be sure to include some pictures soon... thanks for the feedback

    Deathpack Member

    haha its alright we all have our own opinions, i understand that some people don't like to follow VPD charts , or don't believe in them.... but I feel that transpiration plays a big role in how any plant grows... then again that could be my shit filter haha , just gonna have to wait and see...thanks for the feedback :D :D
    Huckster79 and zypheruk like this.

    Deathpack Member

    Thank you for the support :D

    ruwtz Well-Known Member

    I'm keen to see this in action, thats real high supplemented CO2 in veg! It is said fairly regularly that high CO2 in veg stunts stomata development with obvious hindrances throughout the rest of the growth cycle, but I don't know about it as I don't add CO2 in veg.

    Deathpack Member

    It's good to add CO2 in any stage of any plants life , helps with growth if you know what you're doing.. the only CO2 my girls are getting are from their bedtime stories haha, until i set everything up this weekend haha!

    Huckster79 Well-Known Member

    I like vpd as a rough guide, just do go nuts chasing it like its the word of the lord, its a guide... the concept makes perfect sense. What i do is try to roughly follow it until about 3 weeks from finish, then use a week to transition to bone dry and cool finish. Remeber vpd concept is for overall plant health, your goal in last few weeks isnt overall plant health, as shea done growing as a plant, you now want conditions ideal for bud finishing and ripening..

Share This Page