# VPD in perpetual room



## linky (Jan 8, 2017)

I am curious if anyone is growing via VPD chart in a perpetual flower room, if so is the higher temp/humidity an issue in late flower?


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## FamMan (Jan 9, 2017)

linky said:


> I am curious if anyone is growing via VPD chart in a perpetual flower room, if so is the higher temp/humidity an issue in late flower?


I have been wondering the same thing. I will have plants with 4 week difference in my flowering room.


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## Dr. Who (Jan 10, 2017)

Shhhh, The VPD charting works best with gassing...

The best buds come from around 71 F and 35 - 40% RH


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## FamMan (Jan 10, 2017)

Dr. Who said:


> Shhhh, The VPD charting works best with gassing...
> 
> The best buds come from around 71 F and 35 - 40% RH


Gassing? 35-40% throughout flower?


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## Dr. Who (Jan 10, 2017)

FamMan said:


> Gassing? 35-40% throughout flower?


 Gassing = The use of Co2 (it has to be run at high temps and matching Rh values)

YES! All through bloom! Be advised that 35-40% RH will cause more uptake! Feed accordingly!

The 70 F and 35-40% is not VPD "compliant". You get better/denser bud formation and it also helps keep PM at bay!


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## FamMan (Jan 10, 2017)

Thanx! I run c02 so should I be sticking to the vpd chart? @Dr. Who


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## davillains (Jan 10, 2017)

I run co2 and I don't go over 65% ...keep my temps around 75
this is my first run with VPD so I'll know if its rotten in a couple of weeks.


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## linky (Jan 12, 2017)

davillains said:


> I run co2 and I don't go over 65% ...keep my temps around 75
> this is my first run with VPD so I'll know if its rotten in a couple of weeks.


Please do update, interested to know how they are in the final weeks of flower with 65%+ humidity. If I were to set my room back to the VPD chart I would be at ~75% humidity and low 80's temps, just not sure what that will do to late flower buds. (loose buds? mold? etc).


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## Dr. Who (Jan 17, 2017)

FamMan said:


> Thanx! I run c02 so should I be sticking to the vpd chart? @Dr. Who


YES


davillains said:


> I run co2 and I don't go over 65% ...keep my temps around 75
> this is my first run with VPD so I'll know if its rotten in a couple of weeks.


Depending on your Co2ppm......Your plants are not effectively using the extra Co2!

Google that up!


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## davillains (Jan 17, 2017)

Dr. Who said:


> Depending on your Co2ppm......Your plants are not effectively using the extra Co2!
> 
> Google that up!


I'm running it around ~1300 ppm, I don't have enough strength from my lights yet to dial everything in ...but what are you saying ?


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## ruwtz (Jan 17, 2017)

davillains said:


> I'm running it around ~1300 ppm, I don't have enough strength from my lights yet to dial everything in ...but what are you saying ?


He's saying 75F is too cool to make use of CO2 ppm levels higher than ambient. You need those incrementally higher temps to positively affect carbon exchange rates as more CO2 is provided in the atmosphere.


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## davillains (Jan 17, 2017)

that paper on co2 that has been going around and being quoted talks about 30c (86F) but regarding a sativa and the researches did not consider VPD. I think it's logical to assume that since a good vpd promotes respiration and increased metabolism the plant breathes in more co2 as well to photosynthesize. Its not something that happens only in higher temps ...

I don't have log data from the controller to back it up but I swear I get the impression of more frequent spraying from the co2 solenoid valve when I'm hitting a VPD sweet spot, which means the plant is consuming more co2.


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## ruwtz (Jan 17, 2017)

davillains said:


> that paper on co2 that has been going around and being quoted talks about 30c (86F) but regarding a sativa and the researches did not consider VPD. I think it's logical to assume that since a good vpd promotes respiration and increased metabolism the plant breathes in more co2 as well to photosynthesize. Its not something that happens only in higher temps ...


I know which one i'm gonna choose out of logical assumptions and research, but ok.

http://www.plantsneedco2.org/default.aspx?menuitemid=342


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## davillains (Jan 17, 2017)

ruwtz said:


> I know which one i'm gonna choose out of logical assumptions and research, but ok.
> 
> http://www.plantsneedco2.org/default.aspx?menuitemid=342


ruwtz I'm with you on that, but isn't this research flawed if they don't account for vpd ?


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## ruwtz (Jan 17, 2017)

davillains said:


> ruwtz I'm with you on that, but isn't this research flawed if they don't account for vpd ?


Why does one have to preclude the other? I apply high temps for max CO2 and still recognize the value of VPD.

BTW, are you talking about those commonplace VPD charts? They were drawn up for leafy veggies such as lettuce. I've found they're not so easily applicable to cannabis.

If you have a cannabis-specific VPD guide I wouldn't be the only one who would like to see it.


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## davillains (Jan 17, 2017)

ruwtz said:


> Why does one have to preclude the other? I apply high temps for max CO2 and still recognize the value of VPD.
> 
> BTW, are you talking about those commonplace VPD charts? They were drawn up for leafy veggies such as lettuce. I've found they're not so easily applicable to cannabis.
> 
> If you have a cannabis-specific VPD guide I wouldn't be the only one who would like to see it.


Say you have 86F and 50% RH ..this puts your VPD at 21.2 millibars which is not considered "good", meaning you are not promoting respiration/higher metabolism, the stomata are half closed to avoid losing water through evaporation etc etc. What is considered ideal VPD is between 8 and 10 millibars, which translates to 75-80% RH at 86F. It's not a matter of one precluding the other. And unfortunately I don't have a canna-specific VPD chart, from what I've read though this half closing stomata behavior at 12millibars is the same for most plants.

p.s.
can you elaborate on this ? "I've found they're not so easily applicable to cannabis."


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## Dr. Who (Jan 17, 2017)

davillains said:


> that paper on co2 that has been going around and being quoted talks about 30c (86F) but regarding a sativa and the researches did not consider VPD. I think it's logical to assume that since a good vpd promotes respiration and increased metabolism the plant breathes in more co2 as well to photosynthesize. Its not something that happens only in higher temps ...
> 
> I don't have log data from the controller to back it up but I swear I get the impression of more frequent spraying from the co2 solenoid valve when I'm hitting a VPD sweet spot, which means the plant is consuming more co2.



VPD and cannabis is not a rule! I run way off for the BEST results!

As far as your Co2 is concerned.....Your literally _wasting your time and money _if you don't run 90F and 80RH with 1300ppm !! 


ruwtz said:


> You need those incrementally higher temps to positively affect carbon exchange rates as more CO2 is provided in the atmosphere.


IS EXACTLY CORRECT! So was my college prof, the Green house guide, Ed Rosenthal and all the people who have written papers on the subject.....The VPD chart is NOT _gospel!_

GOOGLE THAT!


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## ruwtz (Jan 17, 2017)

davillains said:


> Say you have 86F and 50% RH ..this puts your VPD at 21.2 millibars which is not considered "good", meaning you are not promoting respiration/higher metabolism, the stomata are half closed to avoid losing water through evaporation etc etc. What is considered ideal VPD is between 8 and 10 millibars, which translates to 75-80% RH at 86F. It's not a matter of one precluding the other. And unfortunately I don't have a canna-specific VPD chart, from what I've read though this half closing stomata behavior at 12millibars is the same for most plants.
> 
> p.s.
> can you elaborate on this ? "I've found they're not so easily applicable to cannabis."


VPD charts developed for totally different plants, showing 'sweet spots' not applicable to cannabis or its preferred conditions, "ideal VPD" numbers found only on forums (AFAIK). Hence, this isn't the kind of research i'm inclined to trust over peer reviewed papers and evidence-based study that good and experienced folks like @Dr. Who are telling you about.

Above you state this is your first run with VPD and it is yet to finish, so perhaps this will be a better discussion when you can show us your results instead of conjecture.


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## Dr. Who (Jan 17, 2017)

ruwtz said:


> VPD charts developed for totally different plants, showing 'sweet spots' not applicable to cannabis or its preferred conditions, "ideal VPD" numbers found only on forums (AFAIK). Hence, this isn't the kind of research i'm inclined to trust over peer reviewed papers and evidence-based study that good and experienced folks like @Dr. Who are telling you about.
> 
> Above you state this is your first run with VPD and it is yet to finish, so perhaps this will be a better discussion when you can show us your results instead of conjecture.


BINGO THAT!


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## Dr. Who (Jan 18, 2017)

davillains said:


> that paper on co2 that has been going around and being quoted talks about 30c (86F) but regarding a sativa and the researches did not consider VPD. I think it's logical to assume that since a good vpd promotes respiration and increased metabolism the plant breathes in more co2 as well to photosynthesize. Its not something that happens only in higher temps ...
> 
> I don't have log data from the controller to back it up but I swear I get the impression of more frequent spraying from the co2 solenoid valve when I'm hitting a VPD sweet spot, which means the plant is consuming more co2.



Your not getting it!

The higher temps and the higher humidity. Open the stomata and allow the plant to in take more Co2. The high temp make the plant use more energy faster. The high light concentration of over 48,000 lux allows the plant to photosynthesize faster. These things allow the plant to "utilize" that higher available Co2 ppm.
No temps, no RH increase, and it's like wanting to go faster in a car without stepping on the gas pedal!

That help?


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## Flowki (Jan 18, 2017)

Dr. Who said:


> Your not getting it!
> 
> The higher temps and the higher humidity. Open the stomata and allow the plant to in take more Co2. The high temp make the plant use more energy faster. The high light concentration of over 48,000 lux allows the plant to photosynthesize faster. These things allow the plant to "utilize" that higher available Co2 ppm.
> No temps, no RH increase, and it's like wanting to go faster in a car without stepping on the gas pedal!
> ...


Do plants use enough of the natural co2 in normal conditions or could you increase rh/temp to allow them to use more?.

It's interesting since if you remember that other guys thread who's plants looked bad but budded like crazy, he said he gets like 90+ temps, has a lot of light and I'd assume that would increase humidity too, even if he is trying to keep it down (unless he isn't for that very reason?). But he also mentioned high night temps, maybe they were higher than day temps, somebody else commented on that being an explanation for the yield.


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## Shugglet (Jan 19, 2017)

Dr. Who said:


> Your not getting it!
> 
> The higher temps and the higher humidity. Open the stomata and allow the plant to in take more Co2. The high temp make the plant use more energy faster. The high light concentration of over 48,000 lux allows the plant to photosynthesize faster. These things allow the plant to "utilize" that higher available Co2 ppm.
> No temps, no RH increase, and it's like wanting to go faster in a car without stepping on the gas pedal!
> ...


VPD determines the stomatas actions. The only thin that your scenario would affect is a higher metabolism due to higher temps. The question is whether the plant is capable of photosynthesizing more light at higher co2 and light levels without increasing temps for a boosted metabolism.


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## Dr. Who (Jan 20, 2017)

Shugglet said:


> VPD determines the stomatas actions. The only thin that your scenario would affect is a higher metabolism due to higher temps. The question is whether the plant is capable of photosynthesizing more light at higher co2 and light levels without increasing temps for a boosted metabolism.


Question answer: No, it can not! All direct research states very plainly. That to have the actual benefit of that higher Co2 level. You _*must*_ run higher temps and RH at levels determined by the available Co2 ppm concentrations! Lets not forget that you should be delivering about 48,000 lux to have that 1300 ppm work also! Light intensity, Rh, temps. These all need to be controlled properly to make any increase in Co2 ppm work!

1300ppm
48K of lux
88 - 91 F
78-80% RH

The sweet spot to make it all come together!


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## Shugglet (Jan 20, 2017)

Dr. Who said:


> Question answer: No, it can not! All direct research states very plainly. That to have the actual benefit of that higher Co2 level. You _*must*_ run higher temps and RH at levels determined by the available Co2 ppm concentrations! Lets not forget that you should be delivering about 48,000 lux to have that 1300 ppm work also! Light intensity, Rh, temps. These all need to be controlled properly to make any increase in Co2 ppm work!
> 
> 1300ppm
> 48K of lux
> ...


Can you link to any of this research? Rarely do I see humidity mentioned when discussing co2 supplementation.

Everywhere mentions higher temps but usually fails to amend the typical " ~50% rh" which according to vpd would be way too low.


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## Dr. Who (Jan 20, 2017)

Shugglet said:


> Can you link to any of this research? Rarely do I see humidity mentioned when discussing co2 supplementation.
> 
> Everywhere mentions higher temps but usually fails to amend the typical " ~50% rh" which according to vpd would be way too low.


That's it! You have to run that RH _in_ proper VPD value when gassing! _*TO*_ make that higher gas level work!

Look, I never really "sealed" the grow with the gens in it. I use environmental controllers to "keep" the whole thing running at peak performance. The controllers are set to exhaust at temp/RH limits I set. They go down a pre-programmed amount and the gen's kick in and raise the ppm back to my 1300 setting. The temps/RH rise and when they hit that "too much" start over point. It does...

When growing normally (I might be set to use gas but, don't...It is available if I ever feel the need) I run 70-72F and 35-40 RH. THAT is NOT a "proper" VPD value......The plant does better that way! VPD _*needs*_ to be followed for gassing to work properly.

All three of the factor's work together. unbalance one and the effective use of the Co2 goes down...

Please feel free to google your own papers up on that! MJ growing sites are *NOT* good places for the science (or truth) on that! OH BUT, Ed Rosenthal does discuss and line it out in his Growers Handbook!


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## linky (Jan 20, 2017)

I just want to know if ~75% humidity and low to mid 80's with 850-900 co2 will be okay in late flower/all the way through the cycle, to skurd to just do it


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## Dr. Who (Jan 21, 2017)

linky said:


> I just want to know if ~75% humidity and low to mid 80's with 850-900 co2 will be okay in late flower/all the way through the cycle, to skurd to just do it


Yeah you should be ok there..
Everything increases with ppm increase...
BTW, you need over 84,000 lux for 1500 ppm.....Kinda hard to do! So 1500 ppm of gas is more wasteful then effective....


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## linky (Jan 21, 2017)

Dr. Who said:


> Yeah you should be ok there..
> Everything increases with ppm increase...
> BTW, you need over 84,000 lux for 1500 ppm.....Kinda hard to do! So 1500 ppm of gas is more wasteful then effective....


I don't run it at 1500, anything over 1200 is a waste really anyway.. I run at it 850-950 generally.


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## rickyb0823 (Jan 23, 2017)

Dr. Who said:


> Shhhh, The VPD charting works best with gassing...
> 
> The best buds come from around 71 F and 35 - 40% RH


Interesting. I get my best results with 77 F and 50-60% RH with my co2 ppm set at 1450.


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## Dr. Who (Jan 24, 2017)

rickyb0823 said:


> Interesting. I get my best results with 77 F and 50-60% RH with my co2 ppm set at 1450.


Worked for me at 1Kppm

I had better at 88 and 80+


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## davillains (Mar 1, 2017)

so I harvested my VPD through flower run and I had no mold except for a spot on a bud I had accidentally maimed.
My RH% was 60-65% during daytime and ~40-45% during nigh period where I had the exhaust running non-stop and good air circulation. I was running CO2 at 1300-1500PPM and I will definitively run VPD during flower again. I got 130grams dry from one 40day veg plant under a chinese mars hydro equivelant panel (~150w from the wall) and Dyna-gro FP from start to finish.


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## mjinc (Mar 2, 2017)

I'm currently running my CO2 at 1200ppm, my temps at about 78F and humidity at 55%. Works a treat


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## linky (Mar 2, 2017)

mjinc said:


> I'm currently running my CO2 at 1200ppm, my temps at about 78F and humidity at 55%. Works a treat


If you were going by the VPD chart you would want your humidity to be about 75% at 78F. Is that 78F canopy/leaf temp or ambient btw?


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## mjinc (Mar 4, 2017)

linky said:


> If you were going by the VPD chart you would want your humidity to be about 75% at 78F. Is that 78F canopy/leaf temp or ambient btw?


I have looked at and I've seen the ideal VPD but it's really tough for me to reach. We have very warm days(at the moment) and cool nights so we find we get a ton of condensation if we keep the humidity too high. I also want to avoid ideal conditions for mold which can be a problem where we are.


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## F1_Grower (Mar 4, 2021)

Dr. Who said:


> Gassing = The use of Co2 (it has to be run at high temps and matching Rh values)
> 
> YES! All through bloom! Be advised that 35-40% RH will cause more uptake! Feed accordingly!
> 
> The 70 F and 35-40% is not VPD "compliant". You get better/denser bud formation and it also helps keep PM at bay!


I'm in wk 3 veg.

Should I raise my temps?, rh sitting at 65 to 70% , temps 72 F light off 77 F lights on.

This is my first time hybrid loop. No exhausting outside but between grow rooms with FILTERED fresh cool air intake dedicated lines to each room.


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## F1_Grower (Mar 4, 2021)

F1_Grower said:


> I'm in wk 3 veg.
> 
> Should I raise my temps?View attachment 4843346, rh sitting at 65 to 70% , temps 72 F light off 77 F lights on.
> 
> This is my first time hybrid loop. No exhausting outside but between grow rooms with FILTERED fresh cool air intake dedicated lines to each room.


Here is vpd with 4% lower rh, and slightly warmer. Or are you just describing grower secrets for last wk flower dropping rh like reintroducing 4200k bulbs? Ie terrine production, resins


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## F1_Grower (Mar 4, 2021)

Dr. Who said:


> Question answer: No, it can not! All direct research states very plainly. That to have the actual benefit of that higher Co2 level. You _*must*_ run higher temps and RH at levels determined by the available Co2 ppm concentrations! Lets not forget that you should be delivering about 48,000 lux to have that 1300 ppm work also! Light intensity, Rh, temps. These all need to be controlled properly to make any increase in Co2 ppm work!
> 
> 1300ppm
> 48K of lux
> ...


Hey Dr. Who,

I am very intrigued and curious as to what your research has uncovered. I am saving up for par sensor for my master controller but feel I've hit sweet spot, maybe not?


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## F1_Grower (Mar 4, 2021)

mjinc said:


> I have looked at and I've seen the ideal VPD but it's really tough for me to reach. We have very warm days(at the moment) and cool nights so we find we get a ton of condensation if we keep the humidity too high. I also want to avoid ideal conditions for mold which can be a problem where we are.


Me too am having issues with condesensation forming on 10 x 6 x 9 atrium window which ppl could notice . Ambient temps 40F to 65F and RH 45% to 65% nor cal bay area


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