Archiweedies Is Back At It! 4x4 Tent, LED’s, Coco & Mephisto Genetics
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Kismet
Well-Known Member
I never fuss with my rh being low in humidity for flower? Should i be if i'm running 38 rh in the flower tent?
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- #265
So I’m back after a crash course in Vapor Pressure Deficit. I think I’m picking up the idea here.
Kismet, the quick answer is it depends on what the temps are. If it’s hot in there then your plants are transpiring too fast. That could cause them to drink more nutrients, cause slow growth, etc.
I would say dialing in vpd is to turbocharge the stomata of the plants leaves so that it is operating at peak efficiency.
Here’s the analogy: In really humid environments (think Florida in July) we typically avoid anything that might make us sweat more. By not moving at a normal pace, we drink less fluids. In an arid environment, we aren’t concerned about our ability to breathe and moving around feels pretty good. If the arid environment becomes to dry, we drink more fluids to try to keep the normal pace of movement possible.
VPD is making a lot of sense to me. I used to wonder about people running low humidity in flower. The only way to keep the plant happy with low RH is to lower the temps. Now it’s obvious how we can target purples and other fun stuff in certain chemovarieties.
Kismet, the quick answer is it depends on what the temps are. If it’s hot in there then your plants are transpiring too fast. That could cause them to drink more nutrients, cause slow growth, etc.
I would say dialing in vpd is to turbocharge the stomata of the plants leaves so that it is operating at peak efficiency.
Here’s the analogy: In really humid environments (think Florida in July) we typically avoid anything that might make us sweat more. By not moving at a normal pace, we drink less fluids. In an arid environment, we aren’t concerned about our ability to breathe and moving around feels pretty good. If the arid environment becomes to dry, we drink more fluids to try to keep the normal pace of movement possible.
VPD is making a lot of sense to me. I used to wonder about people running low humidity in flower. The only way to keep the plant happy with low RH is to lower the temps. Now it’s obvious how we can target purples and other fun stuff in certain chemovarieties.
Kismet
Well-Known Member
Temps right now are running 65 to 75. Rh between 38 to 65 but running way less juice so i am happy with that for the moment. Ran outdoors and loved it when my northern lights got purple hairs during a cold snap. Would have been a bust this year outdoors with the rain and humidity. Was lucky outdoors in the past with the weather for sure.
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- #267
Ahh Kismet! I want to share an article with you but I’m uncertain Of the rules regarding that. Let me PM you. This article explains everything in a fairly practical way. The only way I could learn it
The goal is the keep your environment within the “sweet spot” that the charts show.
Once we understand what the plants want and when, then we can hone in on the exact vpd to make sure they are firing on all cylinders.
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- #268
I realized, I should be more clear about VPD because looking around the site I can't find much.
Keep the fact that I am in an un-insulated garage, if you grow indoors VPD still applies but you'll likely not need a heater or an ac for your tent like I have.
Me before VPD and an environmental controller:
"Oh lets see what current temps are. 80 degrees not bad. RH 35%...hmm well could be better. But oh well, its close enough".
"Close enough" based on the fact that we know cannabis thrives between 70F-80F up to 85F without CO2 supplementation.
The RH, depending on what phase the plant is in (ie. seedling, veg, or flower), is low but I had no way to control it before.
Me after learning what VPD is and controlling the environment with a controller:
"Oh 80 degrees? Let me see that VPD chart... Aha! To bring VPD in line I need to raise humidity to roughly 47%RH if I want the plant to be in super awesome transpiration mode."
By looking at the chart, we can see that I needed to raise RH to get into the VPD sweet spot. with an environmental controller, you set the temp and RH, plug your ac's, dehuey's, etc. into the controller and then you can fine tune things.
At this time, I have been experiencing low RH. SoCal has been very dry lately(drier than usual) and because my tent is basically outside, I've seen my RH dip into the teens
. I tried running a humidifier in ther, it was just pumping humidity faster than it could build in the tent because my exhaust fan was sucking it all out(even on low).
I set the knob on my EC to 45% last night, plugged the exhaust fan into the humidity outlet on the EC. When humidity registers 45% the exhaust fan comes on, vents the room below the RH setting by around 5%, and then shuts off again.
The secret, if you grow in a climate controlled environment like you, is to manipulate RH more accurately so that you stay where you need to be from a VPD standpoint. My plants look better right now than they have in days.
![IMG_5570[1].JPG](https://www.420magazine.com/community/attachments/img_5570-1-jpg.1650762/ "IMG_5570[1].JPG")
![IMG_5569[1].JPG](https://www.420magazine.com/community/attachments/img_5569-1-jpg.1650763/ "IMG_5569[1].JPG")
Keep the fact that I am in an un-insulated garage, if you grow indoors VPD still applies but you'll likely not need a heater or an ac for your tent like I have.
Me before VPD and an environmental controller:
"Oh lets see what current temps are. 80 degrees not bad. RH 35%...hmm well could be better. But oh well, its close enough".
"Close enough" based on the fact that we know cannabis thrives between 70F-80F up to 85F without CO2 supplementation.
The RH, depending on what phase the plant is in (ie. seedling, veg, or flower), is low but I had no way to control it before.
Me after learning what VPD is and controlling the environment with a controller:
"Oh 80 degrees? Let me see that VPD chart... Aha! To bring VPD in line I need to raise humidity to roughly 47%RH if I want the plant to be in super awesome transpiration mode."
By looking at the chart, we can see that I needed to raise RH to get into the VPD sweet spot. with an environmental controller, you set the temp and RH, plug your ac's, dehuey's, etc. into the controller and then you can fine tune things.
At this time, I have been experiencing low RH. SoCal has been very dry lately(drier than usual) and because my tent is basically outside, I've seen my RH dip into the teens
. I tried running a humidifier in ther, it was just pumping humidity faster than it could build in the tent because my exhaust fan was sucking it all out(even on low).I set the knob on my EC to 45% last night, plugged the exhaust fan into the humidity outlet on the EC. When humidity registers 45% the exhaust fan comes on, vents the room below the RH setting by around 5%, and then shuts off again.
The secret, if you grow in a climate controlled environment like you, is to manipulate RH more accurately so that you stay where you need to be from a VPD standpoint. My plants look better right now than they have in days.
It seems to be making a big difference
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- #270
Yes, thanks Penny. I was reading and researching after your advice, and another light bulb moment happened. For the first time, I don't feel like my grow location is a handicap for my quality and yield.
I have alot of playing around with the different devices to get it right where I want it, but it is already light years more accurate than it was 24 hours ago.
btw - the two small plants are the Bedroom Cookies. I believe one is expressing much larger indica type leaves than the other. So maybe I will have two different phenos.
@beez0404
I just received this yesterday as well:
Mad scientist mode engaged!
I have alot of playing around with the different devices to get it right where I want it, but it is already light years more accurate than it was 24 hours ago.
btw - the two small plants are the Bedroom Cookies. I believe one is expressing much larger indica type leaves than the other. So maybe I will have two different phenos.
@beez0404
I just received this yesterday as well:
Mad scientist mode engaged!
Lol use the force wisely!
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- #272
Oooh! Laser tested 
.
Those are very happy plants. Great explanation on VPD as well.
.Those are very happy plants. Great explanation on VPD as well.
Your plants and you both
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- #274
Hahah Laser tested for Science!Oooh! Laser tested
Those are very happy plants. Great explanation on VPD as well.
Your plants and you both
Thanks Shed! It opened my eyes and Im stunned we dont have a good post on it here at
I was unable to find any photos, not in my album already, of SLH Shed. Sorry pal
No worries AW. Thanks for checking!
You should start a VPD thread and include your explanation of how it works and relates to people. Put the link in your sig and mention it when folks talk about RH in their threads. You'll get a crowd and you can further the knowledge here!
You should start a VPD thread and include your explanation of how it works and relates to people. Put the link in your sig and mention it when folks talk about RH in their threads. You'll get a crowd and you can further the knowledge here!
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- #276
I'll do a write up and let you check it out, you know so you can tear my grammar to shreds
. I kid, I kid lol. Maybe the community could benefit from the info in a more visible place than my journal.
. I kid, I kid lol. Maybe the community could benefit from the info in a more visible place than my journal.
And your write-up was clear and informative. It's good info to help so many growers who did exactly what you used to do...say "okay, looks good enough."
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- #278
Right on man, I'll do it!! For
!!
Stick your favorite chart in the first post so folks can see how easy it is to understand. "Stay in this zone...easy peasy."
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- #280
Funny you mention that, I have a favorite I found when researching and it was a little different than the one you and Dutchman posted. It has "sweet spot" bands highlighted for clones, veg, and flower for an even easier reference.
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