VPD in perpetual room
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FamMan
Well-Known Member
I have been wondering the same thing. I will have plants with 4 week difference in my flowering room.
FamMan
Well-Known Member
Gassing? 35-40% throughout flower?
Dr. Who
Well-Known Member
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!
davillains
Well-Known Member
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.
this is my first run with VPD so I'll know if its rotten in a couple of weeks.
linky
Well-Known Member
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).
Dr. Who
Well-Known Member
YES
Depending on your Co2ppm......Your plants are not effectively using the extra Co2!
Google that up!
davillains
Well-Known Member
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 ?
ruwtz
Well-Known Member
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.
davillains
Well-Known Member
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.
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
Well-Known Member
I know which one i'm gonna choose out of logical assumptions and research, but ok.
http://www.plantsneedco2.org/default.aspx?menuitemid=342
davillains
Well-Known Member
ruwtz I'm with you on that, but isn't this research flawed if they don't account for vpd ?
ruwtz
Well-Known Member
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.
davillains
Well-Known Member
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."
Dr. Who
Well-Known Member
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 !!
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!
ruwtz
Well-Known Member
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.
Dr. Who
Well-Known Member
BINGO THAT!
Dr. Who
Well-Known Member
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?