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Vpd Survey

Discussion in 'General Indoor Growing' started by 3 balls, Nov 23, 2018.

  1. 3 balls

    3 balls

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    [​IMG]
    Chart attached for quick reference.

    I'm curious to hear some opinions on the importance of staying in the "sweet spot".
    Please respond with a quick:
    Nonsense or Critical

    If you want to elaborate that would be even better!
     
    Ina likes this.
  2. 3 balls

    3 balls

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    Yes, I'm an idiot for not making it a poll. I forgot you could do that until I noticed while clicking post thread.
     
  3. Rootbound

    Rootbound Moderator Staff Member

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    I could add a poll if you want. Need the poll question and answer options.
     
  4. 3 balls

    3 balls

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    I appreciate it but I guess it doesn't need to be a poll. Most people are going to fall somewhere in-between the nonsense and critical marks.
    I do hope people will chime in though. Based on what I read about their setups there are some pretty smart guys on here who don't seem to subscribe to it much and other smart guys who feel it's pretty important. I would bet 90% of growers run RH way way lower than these charts recommend out of fear of PM and rot. I personally know probably 10 guys that would practically need to trade in their de-hue's for humidifiers.
     
    Ina, Herbalise, greencraft and 2 others like this.
  5. I'll chime in. Like you said, I run my RH way lower than the charts because that is how dry it is here in the winter and I would be afraid of PM if it was in the sweet spot of the chart. My current RH is 20% :opps: but we have an extremely dry, cold, high pressure day today. I am not a big fan of humidifiers so, it is what it is.
     
  6. JWM2

    JWM2 Premium Member Supporter

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    I don’t use the chart myself persay but I’m within range. I’m trying to keep my RH low but I’ve got ample air circulation to make up for it. If the air was stagnant I’d be more worried but the air is exchanged 3-4 times per minute in my rack with fans blowing on the plants at all times so all is well thus far.

    Keeping my temps up has been a bit of an issue since installing highly efficient dimmable LEDs. But not a big deal. I’m used to fighting high temps so it’s kind of refreshing to have the inverse.
     
    greencraft, 3 balls and Erick31876 like this.
  7. It's not scientifically backed and i couldn't find any difference in side by sides. The resin is to retain moisture, defend uvb, defend life forms, etc. By science, a dry room is easier for the plant to exhaust in, which is easily remedied by watering the medium. High humidity rates make it more difficult for the plant to breathe and gas off. There's really no reason to put your humidity into mold thriving conditions for your plants benefit. It's nonsense. There are a ton of these myths. Few more are that plants suffer inherently from being rootbound, if you let your coco dry out its cec goes crazy(coco reacts with nutrients like peat does(slightly differently), if you let peat or soil dry out does it get crazy?), and the way over statement of ph. Crack a seed into dwc and make the water 8ph, it'll be fine until you change the ph. Another common myth is that roots play a part in purpling. These are stupid easy to test. Got my room to 50 with thermometers in soil and top of medium and big surprise, still 70°. Don't listen to people, research the science. Learn how a plant reacts to humidity and what it's actually doing and you should understand that this is nonsense. A plant is kind of like a blowup raft with tons of sections full of air. It opens valves to offgas moisture and replace it and maintain a certain amount of pressure. If the air is full of water like the leaf is, simple science says the plant now has a harder time exchanging gases with the outside air. That's negative to the plant. Ive grown in 20% for literally 2 years with no ill effects and side by sides with chambers i made to test this showed me the number isn't important, but changing it does. The biggest thing i learned from all my tests is that the plant dislikes change more than any of these myths. Consistent environment is more important than any environment variable by exponential amounts. VPD irrelevant in nonsealed rooms and probably still there, just can't say cause i haven't tested it. The plant can control what moisture leaves it but not whats out there. So even in an ultra low humidity sealed room the plant can just exchange for very small periods. If the air is too humid, it can be open all day and maybe not let out enough moisture still. Equilibrium is not the goal, exchange needs to occur. Vpd is chasing equilibrium.
     
    Last edited: Nov 23, 2018
  8. CrimsonEcho

    CrimsonEcho Premium Member Supporter

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    70% rh is not too humid. I don’t really know how you came to the conclusions you did but, these numbers are just a somewhat ideal margin for a grower to set his area at.
    I’m not sure if you can grow a plant in dwc at 8ph, like a full grown healthy cannabis. If you tried that i’ll be happy to see your results.
    You may have grown at 20% and get satisfying results, plants adapt if they need to, but saying vpd is nonsense is going a little too far imo. Your claim that the plant will just take in more water is true, if the rh is low, but it will also take in nutrients too. Which may cause burns and lockouts in the long run.
    Its better to give any plant a comfortable environment to grow. Just cause you had success with 20% rh doesn’t mean its ideal. I’ve seen people getting all kind of weird symptoms from low rh.
    Its just, these are opinions, yours and mine. I think this should be underlined.
    Again, you can say if a plant has hard time exchanging air with high humidity (70% is not imo), you can also say low rh causes stomatas to close in order to conserve water which distrupts the gas exchange and photosynthesis. Plant can exchange gas and moisture at 70% better than 20% imo.
    To my knowledge coco coir has significantly lower cec value compared to peat by the way. Not a coco grower but just saying. Its not very much like peat in many senses.
     
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  9. PharmHand

    PharmHand

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    The vpd chart is most definitely “scientifically backed” lol it was developed over years of research by peer reviewed university studies. My advice to someone relatively new to growing would be to get off the grow forums and learn the fundamentals of horticulture so you’re able to differentiate proven scientific facts from the regurgitated hearsay that is perpetuated on forums
     
  10. There are obvious limits. I was going to add that but got busy. My tests aren't meant to be taken on faith. You didn't answer with any evidence though. I have proven to myself that the limits are far more favorable to the low humidity side, than the high. That is pure opinion. I agree that 70%isn't high and i didn't mean to imply you would inherently damage your plant by chasing 70% rh. That's pretty typical range for Pakistan. My chief point was that you stand to do more damage chasing a rh and making your environment inconsistent than just growing at 20%. I honestly agree with you that nonsense is too far. I tend to speak my own language at times and this is a case of that. You don't have to understand, but yeah my point was be consistent and off these "ideal" numbers vs following every trope and ruining the consistency. I do think the way people parrot and shout common myths is nonsense though.
     
  11. Really? Because the 4 studies i looked at don't have any realistic evidence that this will effect flower size or resin or even plant health. From a popular one "Although atmospheric vapour pressure deficit (VPD) has been widely recognized as the evaporative driving force for water transport, the potential to reduce plant water consumption and improve water productivity by regulating VPD is highly uncertain. To bridge this gap …"

    This stuff is developing science and who knows if it's even relevant to cannabis. We don't understand a TON about plants or cannabis.
     
  12. CrimsonEcho

    CrimsonEcho Premium Member Supporter

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    You’re claiming its better to have low rh compared to high but i have to disagree. I can back my claim with a scientific fact right now. The low rh causes the stomata to close which distrupts gas exchange. Now resin and flower production is a different thing. If you’re looking at this charts on the basis of resin production i doubt you’ll find much. You are inducing stress to heighten resin production, thats a know fact. This is for a healthy plant in veg and maybe up until the last 2 weeks of flower imo. Then you can induce stress and cause the heightened resin production its your call. You’re thinking whats “healthy” for you (more resin). This chart is for plants to be healthy.
     
  13. PharmHand

    PharmHand

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    Based solely on the wording of what u quoted I would say that study was discussing water conservation. I want fat sticky buds @Daikokuten
     
  14. You're really closing the spectrum of what i'm saying. I didn't say low is better, i said 70% is normal for a place it has adapted to. I said chasing a rh at the sacrifice of being consistent is worse than achieving a perfect vpd on demand 247 for a new grower who doesn't even understand vpd. You're adding and removing a lot of what I'm saying. My opinion is that starting and keeping 20% rh is not stressful past maybe an initial adaptation period. That's pure opinion.
     
    greencraft likes this.
  15. Point was they all conclude the same. "Vpd is accepted as influence, though not proven. Here's how this study tried to find more information to bridge thegap". This is not well proven, well understood science like gravity or something.
     
    greencraft likes this.
  16. CrimsonEcho

    CrimsonEcho Premium Member Supporter

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    Ok i’m not going to manipulate what you’re saying. Wasn’t trying to. You say “chasing a rh at the sacrifice of being consistent”, can you eloborate on this? What do you mean by that?
    In my opinion if you have perfect vpd 24/7 you pretty much have a consistent environment.
    Vpd chart is pretty much in place to provide this consistency.
     
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  17. Jimster

    Jimster

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    I've been growing for many years and deal with moisture levels that are lower than recommended...according to the chart. During the winter, humidity drops really low initially, when the grow is beginning. Because the air is so dry, I often see some browning tips on a few leaves, but as the plants grow and they start to raise the humidity from their transpiration, the browning goes away. During the summer, I have AC and the humidity is typically 30% and not much higher. I've always had excellent results, although the colder winter temps (typically 60/night and 75/day cause some strains to display the purple highlights...but it has to be fairly cold compared to normal temps to notice it. With the current cold snap, my setup is 71F and 33% humidity, but will only swing about 5 degrees from these norms regardless of outside temps due to good insulation and ventilation.
     
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  18. Not to sound up my own ass, but i think i again am speaking casually and not specific enough. I'm answering to op basically and even mimicking his language in the first post. I'm seeing a new grower save that chart. Build it up to himself. Buying a humidifier and starting to mess with his girls chasing a chart he doesn't understand. I believe vpd is a major driving force in plants. I don't believe we know enough about it or plants or cannabis to say if it's relevant in an indoor garden situation. It's not something i would spend money on remedying or back it like it's proven science. Now, i don't use my anecdotal as real truth, but i couldn't get rh to do anything to a cut ive grown and harvested for 8 years, unless i started changing it during flower and that wasn't even visible, it just had "worse" sap tests.
     
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  19. PharmHand

    PharmHand

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    It’s ironic you chose gravity, one of the least understood of all fundamental forces. No matter what the subject, there’s always more to learn. But VPD is well studied and very observable. You put various plant species in extremely well controlled conditions and make observations recreatable by other experts in the field. By and large most agree.... Science
     
    Last edited: Nov 23, 2018
  20. Except that's not what is in the studies you're blindly referencing. You described gravity, not vpd affecting plants. I also should clarify that studies are time consuming and ive actually found studies going both ways on this. Which is why my opinion is simply, we don't know enough for me to back it or act on it. I think it could confuse a new grower and cost them money and medicine. That's my primary priority here.