Follow VPD chart during flower?

[Aqua Man]

My rec is to keep it above 45 and below 60 so it is in a safe stable range. Just like temps need to be kept tight.

Plants like stability.

I'm betting you follow right smack in line with VPD and don't even know it

 

[Aqua Man]

Also quick note ppl VPD only matter during photosynthesis as plants respire during the dark period but hardly transpire. So humidity at night should be lower by 10-15% than during photosynthesis if possible as they dont need the humidity and you can reduce the ideal conditions for germination of mold and fungal spores.

 

[CF89]

Without my humidifier my tent is around 35% humidity but I’m 4 weeks into flower. That’s even after watering till runoff.

with the humidifier on it’s around 60% and seems to clog my carbon filter and the exhaust outlet air seems weaker when the humidifier is going and it’s at 60% RH.

not sure I even want 60% RH at this stage in flowering. I think 30-40% is perfect anyways so I may not even need my dehumidifier.

I think the bigger kingbrite light I just installed that creates a lot of heat changes the humidity during the day. It’s never been so low.

 

[redshift75]

SO i will note that i just realized i have them mislabeled in my govee app. Tent listed as B2 is c2 and C2 is b2 I didnt flip the names before i took screen shot.

Its not optimal in the slightest. More a point to"can it be done?" yes.

Im more experimenting with the extremes. I call the environment an "arctic rainforest". To the point that you should strive to maintain optimal. but you can make it work if it doesnt. I think my signature sums up my belief.

"I don't think you'll ever have a perfect world because we humans are prone to error, and so we're always in search of an upgrade." -Henry Rollins"

Lots of people will tell you things cant be done, when they mean they shouldnt be done. But it does not mean you can't do it. Im not sure even if i had perfect what the change would really be? maybe a few more grams? i guess the harvest will tell. But i feel like im in control of my grow and nothing has gotten out from under me or been left to rot. I do a lot for those tents. More then i have to. But harvest season is done for me. So all i have left for my time is cannabis and its fun. I dont know what i cant do, til i fail at trying to do it.

 

[Aqua Man]

Also just to complicate this further. Other factors like light especially play a role. You will be able tonpush plants harder with more light if you dial in the VPD but if your not pushing them past the point in a we'll call it "poor VPD" impacts the ability to utilize the light you may not see negative effects.

Where if in a poor VPD and you are giving a bit more light than they can handle changing the VPD may make you an absolute believer as you can see them handle more light and no ill effects. So if your lighting isn't driving them as hard and your in a mediocre range VPD your not likely to see any positive or negative effects. But now increase that light and see light stress which can be reduced through VPD to a point of course as the plant can photosynthesize more efficiently

 

[Aqua Man]

SO i will note that i just realized i have them mislabeled in my govee app. Tent listed as B2 is c2 and C2 is b2 I didnt flip the names before i took screen shot. View attachment 1046216
View attachment 1046219

View attachment 1046217View attachment 1046218




Its not optimal in the slightest. More a point to"can it be done?" yes.

Im more experimenting with the extremes. I call the environment an "arctic rainforest". To the point that you should strive to maintain optimal. but you can make it work if it doesnt. I think my signature sums up my belief.

"I don't think you'll ever have a perfect world because we humans are prone to error, and so we're always in search of an upgrade." -Henry Rollins"

Lots of people will tell you things cant be done, when they mean they shouldnt be done. But it does not mean you can't do it. Im not sure even if i had perfect what the change would really be? maybe a few more grams? i guess the harvest will tell. But i feel like im in control of my grow and nothing has gotten out from under me or been left to rot. I do a lot for those tents. More then i have to. But harvest season is done for me. So all i have left for my time is cannabis and its fun. I dont know what i cant do, til i fail at trying to do it.

Notice how your temos go down and humidity goes up as the lights go out?

 

[redshift75]

Also just to complicate this further. Other factors like light especially play a role. You will be able tonpush plants harder with more light if you dial in the VPD but if your not pushing them past the point in a we'll call it "poor VPD" impacts the ability to utilize the light you may not see negative effects.

Where if in a poor VPD and you are giving a bit more light than they can handle changing the VPD may make you an absolute believer as you can see them handle more light and no ill effects. So if your lighting isn't driving them as hard and your in a mediocre range VPD your not likely to see any positive or negative effects. But now increase that light and see light stress which can be reduced through VPD to a point of course as the plant can photosynthesize more efficiently

I think thats the key people miss with VPD is its about pushing them to the extreme.(for the hard run vpd mindset) Which honestly most people dont set themselves or their grow up for those real pushes. I put myself in that category. But there is a general baseline to maintaining optimum always. I dont really put that as vpd in my mind.

Notice how your temos go down and humidity goes up as the lights go out?

Yes, definitely. most times thats when i close the tents back up for the day. lots of factors to why these tents arent where i want them right now. I ultimately did not factor the heater and their distance when i plumbed them. IDK why i put them in front of a propane fireplace. BUt then i also ran out of propane and they are behind because of flu. So im just rolling with it.


I was running dehumidifier setup between both those tents but given all the environmental factors it was just sucking the water out of the pots and running them dry vs drying the tent due to lack of heat.


When life gives you lemons, You grow lemon haze i say. :)

 

[visajoe1]

Good discussion. I'll have to find some articles I've read, but what I took from them was Leaf VPD has an effect on the metabolism/transpiration of plants. As Leaf VPD increases, the plants ability to metabolize food decreases (e.g. when we see nute burn with low/mid EC) causing salts to buildup in leaves. Increased Leaf VPD also lowers ability to fight pests/molds. If Leaf VPD is too low, growth may become negatively impacted (e.g. winter).

I'm a believer in VPD since I committed to it. Below is the guidelines I aim for, its not a crisis though if things sway outside of the limits at times.

Seedling/clone 0.4-0.8

Veg 0.8-1.1

Early flower 1-1.4

Late flower 1.3-1.5

 

[Aqua Man]

I think thats the key people miss with VPD is its about pushing them to the extreme.(for the hard run vpd mindset) Which honestly most people dont set themselves or their grow up for those real pushes. I put myself in that category. But there is a general baseline to maintaining optimum always. I dont really put that as vpd in my mind.

Yes, definitely. most times thats when i close the tents back up for the day. lots of factors to why these tents arent where i want them right now. I ultimately did not factor the heater and their distance when i plumbed them. IDK why i put them in front of a propane fireplace. BUt then i also ran out of propane and they are behind because of covid. So im just rolling with it.


I was running dehumidifier setup between both those tents but given all the environmental factors it was just sucking the water out of the pots and running them dry vs drying the tent due to lack of heat.


When life gives you lemons, You grow lemon haze i say. :)

Absolutely VPD is all about optimizing.... its not a must per se but does become more crucial the harder we push plants and the faster our growth rates are. I used to have a really hard stance on it because I could see it in my hydro with co2 so evidently but as time goes on and I have experimented in different medias I have a better understanding of it and how many feel its not all the hype its built up to be. In the end if you are pushing your plants limits it makes all the difference in the world and if your not its a lot more forgiving than us VPD guys (myself included) make it out to be.

 

[Aqua Man]

Good discussion. I'll have to find some articles I've read, but what I took from them was Leaf VPD has an effect on the metabolism/transpiration of plants. As Leaf VPD increases, the plants ability to metabolize food decreases (e.g. when we see nute burn with low/mid EC) causing salts to buildup in leaves. Increased Leaf VPD also lowers ability to fight pests/molds. If Leaf VPD is too low, growth may become negatively impacted (e.g. winter).

I'm a believer in VPD since I committed to it. Below is the guidelines I aim for, its not a crisis though if things sway outside of the limits at times.

Seedling/clone 0.4-0.8

Veg 0.8-1.1

Early flower 1-1.4

Late flower 1.3-1.5

yup thats a lot of it. Of course strain will also play a role which end of the spectrum they like. They are so many moving parts to it that its a very complicated subject. Like most things in cannabis related topics. But there are reasons some feel it works and some don't. a large part is the importance of leaf temps. Most will find if you take leaf temps into account your RH should be much lower than what is dictated by the online charts and lighting has a lot to do with leaf temps when comparing HID to LED and IR supplements. Again these are targets and that doesn't mean you can't grow problem free outside of them.

 

[JWM2]

50% RH is way different at 70 degrees than 80 degrees. VPD better explains where all the moisture is going. Ever wonder why your plants aren’t drinking as much or are drinking more water than normal? VPD knows. Sure we might not need to know our pH, alkalinity, light intensity, etc to grow good weed but each tool we add to our toolboxes help us grow to our potential and help us spot issues earlier than we might detect otherwise.

 

[redshift75]

Absolutely VPD is all about optimizing.... its not a must per se but does become more crucial the harder we push plants and the faster our growth rates are. I used to have a really hard stance on it because I could see it in my hydro with co2 so evidently but as time goes on and I have experimented in different medias I have a better understanding of it and how many feel its not all the hype its built up to be. In the end if you are pushing your plants limits it makes all the difference in the world and if your not its a lot more forgiving than us VPD guys (myself included) make it out to be.

Thats how i feel. There is a certain level you have to do more things. Its all what you are going for. Most people start like "i want to be mario andretti" then realize you can be some kid racing go karts and have just as much fun. or something to that effect :)


If im talk strict settings and measures of control. Of course every grower is trying for optimum. But its the classic " happens"


Most people should know of it. But if you use it or dont its fine. Id say a better option is just stick to the rule of thumb of temp and RH vs that chart til you need to push it and use it.

For me it can be guidance for me to cross reference when i may be going too hard. or too little. I can cross my data, point at something and say 'thats prolly it'. I have the chart. Just cant say i use it. If i went co2 and to the max. Id probably definitely run my grow based on it. Since ive never really done indoors. Im still at my learning curve. But my mentality comes from "i cant control it outside, so what does it matter... honestly?". But with that comes the knowledge that i do understand how it works and it does matter.

outside the past few weeks in flower the entire grow would be considered optimal to that chart. So really if you are doing everything how you know you should. You kind of always fall in the category? maybe?



Then factor all those great points by aquaman. Those are the times you can really hit the proverbial Nitrous button on the right day to stimulate some good results.

edit: just a quick note. Not against it by any means. Just i dont personally follow it to a hard line. Like everything we do its all personal choices. I use my experience to dictate where its at. I also understand the risks and am willing to take them on my own grows. So dont do what i do assuming you can do it the same. I have some pretty hearty genetics i attribute my ability to put them through extremes. Its good to know what the genes you are working with can do. So please do whats always in the best interest of your grow and your needs.

 

[Aqua Man]

@MIMedGrower i gonna have to get back to you on links. But for shits and giggles what the temp of your rooms and humidity?

I do agree that yields are minimally affected by VPD itself. But more in a round about way by allowing you to push more light even as slight as that may be. If the VPD is around 1.0 KPA +/- I would say 0.6 )quite possibly more on the high end) we generally don't see issues unless pushing the plants hard. The biggest thing i feel VPD is good for is being able to push harder and believe it or not prevention of mold/fungal infections.

 

[Aqua Man]

Thats how i feel. There is a certain level you have to do more things. Its all what you are going for. Most people start like "i want to be mario andretti" then realize you can be some kid racing go karts and have just as much fun. or something to that effect :)


If im talk strict settings and measures of control. Of course every grower is trying for optimum. But its the classic " happens"


Most people should know of it. But if you use it or dont its fine. Id say a better option is just stick to the rule of thumb of temp and RH vs that chart til you need to push it and use it.

For me it can be guidance for me to cross reference when i may be going too hard. or too little. I can cross my data, point at something and say 'thats prolly it'. I have the chart. Just cant say i use it. If i went co2 and to the max. Id probably definitely run my grow based on it. Since ive never really done indoors. Im still at my learning curve. But my mentality comes from "i cant control it outside, so what does it matter... honestly?". But with that comes the knowledge that i do understand how it works and it does matter.

outside the past few weeks in flower the entire grow would be considered optimal to that chart. So really if you are doing everything how you know you should. You kind of always fall in the category? maybe?



Then factor all those great points by aquaman. Those are the times you can really hit the proverbial Nitrous button on the right day to stimulate some good results.

Yeah i agree. There is a real problem with VPD info out there and it leads ppl to run RH values way to high. Its these dam charts floating around that are not tailored to the persons grow. Leaf temp is a must when using it.

 

[redshift75]

Yeah i agree. There is a real problem with VPD info out there and it leads ppl to run RH values way to high. Its these dam charts floating around that are not tailored to the persons grow. Leaf temp is a must when using it.

too many people see data as a Point A to point B. When its more like Mile/Kilo marker 1 to hopefully 100. You can simplify it. but... is it ever really that simple? <---- this leads (for me at least) greater disappointment when i personally fail.

 

[visajoe1]

Some stuff looking at VPD influence on plants, to help one understand the relationship. We all have to draw our own conclusions how this translates to cannabis

Frontiers | The Plant-Transpiration Response to Vapor Pressure Deficit (VPD) in Durum Wheat Is Associated With Differential Yield Performance and Specific Expression of Genes Involved in Primary Metabolism and Water Transport

The regulation of plant transpiration was proposed as a key factor affecting transpiration efficiency and agronomical adaption of wheat to water-limited Medi...

www.frontiersin.org

Understanding VPD and Transpiration Rates for Cannabis Cultivation Operations | Cannabis Science and Technology - Cannabis Industry News, Insights

This article explores how vapor pressure differentials (VPD) affect transpiration rates in cannabis plants. Understanding of VPD at different temperatures and relative humidities, and its effect on this process, is important to gain maximum plant growth.

www.cannabissciencetech.com

Vapor Pressure Deficit and Indoor Growing Part 1: What is VPD?

Vapor Pressure Deficit (VPD) can help growers fine tune water flow through a plant. It acts as a "control dial" for cannabis cultivators.

www.questclimate.com

https://www.longdom.org/open-access/substrate-effects-on-plant-transpiration-rate-under-several-vapourpressure-deficit-vpd-levels-2157-7471-1000369.pdf

 

[MIMedGrower]

@MIMedGrower i gonna have to get back to you on links. But for shits and giggles what the temp of your rooms and humidity?

I do agree that yields are minimally affected by VPD itself. But more in a round about way by allowing you to push more light even as slight as that may be. If the VPD is around 1.0 KPA +/- I would say 0.6 )quite possibly more on the high end) we generally don't see issues unless pushing the plants hard. The biggest thing i feel VPD is good for is being able to push harder and believe it or not prevention of mold/fungal infections.

Depends on season a bit but like i said as guidelines. 75-77 degrees and 45-60% rh.

But my results are not the point. I grow in a ventilated room under only medium high light intensity.

My point is all the actual humidity testing i have found show no difference in results and all vpd info seems to be from companies selling something or a site with an agenda for the cannabis industry and i havent found any test proving it at all.

And i believe that is because it is contrived and not factual info. The “vapor pressure” is not the only factor for plant transpiration. And it is not really one of the normally mentioned important ones like temperature or nutrient availability.

Is humidity even part of the plant law of minimums?

 

[Aqua Man]

Depends on season a bit but like i said as guidelines. 75-77 degrees and 45-60% rh.

But my results are not the point. I grow in a ventilated room under only medium high light intensity.

My point is all the actual humidity testing i have found show no difference in results and all vpd info seems to be from companies selling something or a site with an agenda for the cannabis industry and i havent found any test proving it at all.

And i believe that is because it is contrived and not factual info. The “vapor pressure” is not the only factor for plant transpiration. And it is not really one of the normally mentioned important ones like temperature or nutrient availability.

Is humidity even part of the plant law of minimums?

I agree with you on alot of that. 0.7-1.2 would be the kpa range you sit guessing leaf temps of about 5f cooler.

Absolutely a good range to be. I'll get ya the studies in the next day or 2.

I agree it's a tiny tiny part of the overall grow needs and so many other things affect transpiration rates also. But temp and humidity i would say are the 2 biggest driving factors if the others are not impeding transpiration

But yea I will concede that often times its given to much emphasis and as long as you stay in a reasonable range around 1.0 kpa plants do well in most grow rooms

 

[MIMedGrower]

I agree with you on alot of that. 0.7-1.2 would be the kpa range you sit guessing leaf temps of about 5f cooler.

Absolutely a good range to be. I'll get ya the studies in the next day or 2.

I agree it's a tiny tiny part of the overall grow needs and so many other things affect transpiration rates also. But temp and humidity i would say are the 2 biggest driving factors if the others are not impeding transpiration

Ok i will read of course but humidity is only proven to not have much impact on yield or quality in 25 odd years of grow books and testing.

Temperature on the other hand has a huge impact.

There are 10 pound plants on the coast of oregon and in the mountains of colorado. See what im saying?

 

[Aqua Man]

Ok i will read of course but humidity is only proven to not have much impact on yield or quality in 25 odd years of grow books and testing.

Temperature on the other hand has a huge impact.

There are 10 pound plants on the coast of oregon and in the mountains of colorado. See what im saying?

VPD is both temp and humidity. I agree temps are a huge huge factor. Thats the first thing I get right... next is the humidity and I do that using VPD. First I get my leaf temos where I want then adjust the humidity to match VPD.