I would like to say I think this vpd curve gets adjusted out slightly with everything we are giving our plants. I know the extra K (allows for movement of more water and heavier transpiration) in potassium silicate and the silica (bigger highways for the water in the plants) allows me to run my room a little warmer and dryer than I should.

after reading into VPD and actually seeing the SIGNIFICANT benefits of running 'high' humidity (65-75% in flower) I now truly believe what everyones favorite 'JackMayOffer' was talking about.

i'm not going to get too deep into this conversation and keep it as simple as possible, just as simple as the results i saw from roughly following the VPD chart were. by roughly, all i mean is that i overpowered my AC in a few rooms and was somewhat accidentally yielding 2+ a light in a commercial grow with little to no plant training and hardly any effort (aka vegging for 3-4 weeks and topping once or twice)

Overpowering the ACs in my first 'testing' room wasnt was intentional, but the results from growing in a room with 65-75% humidity wasnt. This 'test' room had been neglected and fed inconsistent formulas way off my usual feed chart and I only fed A+B, calmag, and a PK booster. I was growing in cocobeds DTW... only part was that I didnt drain to waste. I had reused the coco for 3-4 cycles and by the time I decided to flush the beds for once the runoff were reading anywhere from 3000-4000+ PPMs... but somehow hte plants didnt lock out. In my other rooms without proper insulation, the ACs (5 tons for 12 SE bulbs) were struggling because they were running way more often than they were supposed to. The effect of constant AC is that its dehumidifying the air to the range of 40-50%. In those rooms I constantly had thin, purple and stiff plants when I first transplanted up until 2 weeks later when they were large enough to perspire and raise the RH into the 60%s. Those plants wouldnt more often than not lock out if the medium hit around 2500 PPMs and I couldnt understand why even though I was feeding them the full line of nutes from different companies in separate cycles.

Cycle after cycle these rooms that were being babied were always struggling to hit my goal of 2 a light while getting more expensive nutrients and HOURS of training, trellising and more. The neglected room was effortlessly hitting 2+ a light every damn time with a new roster of strains practically every cycle. Didnt matter if it was a mix of OGs, hybrids, short indicas with 1-2 tables with stunted plants that were didnt even trim and account into the final numbers. We still got 30+ out of a 15 light room.

Finally after over a year and being exposed to the VPD chart I learned why this room was crushing it.

just re-read my post above... thats what happens when you wake up at 8AM and stay up til 3AM. so many errors. hopefully you guys can understand what i was trying to convey.

ArcticOrange said:

I would like to say I think this vpd curve gets adjusted out slightly with everything we are giving our plants. I know the extra K (allows for movement of more water and heavier transpiration) in potassium silicate and the silica (bigger highways for the water in the plants) allows me to run my room a little warmer and dryer than I should.

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This is a key factor in the ability to grow perfectly good meds without adherence to vpd parameters.

@chinqlinq :

So, you are saying that by following the VPD chart your yield increased?

I think he's saying that he now understands why the one room was doing so well whereas the others were struggling. VPD was the difference.

chinqlinq said:

just re-read my post above... thats what happens when you wake up at 8AM and stay up til 3AM. so many errors. hopefully you guys can understand what i was trying to convey.

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I got it.

Seamaiden said:

I think he's saying that he now understands why the one room was doing so well whereas the others were struggling. VPD was the difference.

I got it.

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exactly.

its always been preached that having your room environment 'dialed in' was the most important part before you start to buy all these expensive nutrients and gadgets, yet so many people - including myself - overlooked it. getting your VPD dialed in will most likely solve SO many deficiency/growth problems and boost vigor, yield and potentially quality SIGNIFICANTLY.

you will most likely want to drop humidity in the last few weeks of flower once they bulk, especially if you pack your plants in and have dense foilage.

even OGs that were showing cal deficiencies the moment i used less than 6-7 MLs of calmag were cured just by following the VPD chart. now they look perfectly green with 5 MLs max.

chinqlinq said:

even OGs that were showing cal deficiencies the moment i used less than 6-7 MLs of calmag were cured just by following the VPD chart. now they look perfectly green with 5 MLs max.

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Ok, that's a "WHOA!" for me. Great information to keep tucked away in one's pocket!

chinqlinq said:

exactly.

its always been preached that having your room environment 'dialed in' was the most important part before you start to buy all these expensive nutrients and gadgets, yet so many people - including myself - overlooked it. getting your VPD dialed in will most likely solve SO many deficiency/growth problems and boost vigor, yield and potentially quality SIGNIFICANTLY.

you will most likely want to drop humidity in the last few weeks of flower once they bulk, especially if you pack your plants in and have dense foilage.

even OGs that were showing cal deficiencies the moment i used less than 6-7 MLs of calmag were cured just by following the VPD chart. now they look perfectly green with 5 MLs max.

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I'd like to thank you and the rest of the farm for this valuable information. I've always done well, but ever since I sealed my room and added Co2, I've had nothing but problems. I always got lucky at the sweet spot of running 74/75 F at 50-55% rh. Now I realize at canopy temp of 84, I shoukl be running humidity much higher. I'm running a cross that I made of motorbreath (sfv og x chemdawgd) x Bubba76 and she is the most finicky plant that I've grown. She had constant cal mag issues (calcium lockout) and I finally realize it's because my VPD was out of whack. Even though I've been doing this a while, it's always nice to up my game. Thanks again folks.

fishwhistle said:

Not to mention its a pain in the ass,more equipment,RO water to not make a mess on your lamps or glass etc.

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RO water wont leave mineral deposits. I use my AC condensate in my humidifiers...super low PPMs and they never clog.

chinqlinq said:

after reading into VPD and actually seeing the SIGNIFICANT benefits of running 'high' humidity (65-75% in flower) I now truly believe what everyones favorite 'JackMayOffer' was talking about.
The effect of constant AC is that its dehumidifying the air to the range of 40-50%. In those rooms I constantly had thin, purple and stiff plants when I first transplanted up until 2 weeks later when they were large enough to perspire and raise the RH into the 60%s. Those plants wouldnt more often than not lock out if the medium hit around 2500 PPMs and I couldnt understand why even though I was feeding them the full line of nutes from different companies in separate cycles.

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This is gold. I've been having the exact same probs with my rooms for a few years and just now realizing that all the AC is sucking the moisture out of the plants. Sorry for those above who think 20-30% RH is adequate for cannabis...you're wrong. You can limp along at that level of humidity but you won't see the optimum results. Just invested in a couple industrial humidifiers and already seeing my girls happier....

sixstring said:

I mean if you want growth so fast that the leaves grow faster than the thc can cover the leaf then vpd is the way to go.but ime lower rh beings on more resin.of course thats just my own observation lol

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I've been running 72F canopy temps (max) and 15% RH for years now. When I run cuts from other growers, they don't recognize the end product as coming from their genetics. The terpene and cannabinoid production, as well as the trichome density, is significantly higher.

You want a lot of plant? High RH, High temps will get you that. You want significant quality, low temps and low rh are what you want. ;)

Think of each plant as growing only a certain number of trichomes on itself. The more *plant* you grow, the further apart the trichomes are. The less plant you grow, the denser they appear. I prefer to medicate with trichomes, not plant, and smoking my flowers tastes very close to what hash from the same plant tastes like. Extremely little *burnt plant* taste and a super lightweight ash. ;)

Edit: Yes... you have to veg longer as there isn't a massive *stretch* when you flip to flower.

canopy temp understanding is important to me atm.

Douglas.C said:

Think of each plant as growing only a certain number of trichomes on itself. The more *plant* you grow, the further apart the trichomes are.

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Sorry, I'll have to disagree with this. The size of the cells are the same either way. The number of the cells are the only thing that changes.

MidwestToker said:

Sorry, I'll have to disagree with this. The size of the cells are the same either way. The number of the cells are the only thing that changes.

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Disagree all you like, then grow the same strain in high vdp (high temp/RH), then moderate vpd (low temp/RH) and see the difference. Same strain is frostier in the low temp/RH. I used to think it was a genetic trigger, now I know it's just plant growth rates.

BTW. When you don't see a difference in terpene production/retention, your other variables are off.

Douglas.C said:

Disagree all you like, then grow the same strain in high vdp (high temp/RH), then moderate vpd (low temp/RH) and see the difference. Same strain is frostier in the low temp/RH. I used to think it was a genetic trigger, now I know it's just plant growth rates.

BTW. When you don't see a difference in terpene production/retention, your other variables are off.

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Lower temps and RH in late flower is one thing but in veg VPD does play a role in production of mass. The point i'm trying to make is that the size of the cells don't change, you just have more cells. So it still comes down to the genetic potential of the strain.
I grow in both cold and warm rooms, In fact I just harvested 4 plants in a max of 62 degrees and a RH between 20-30 %.
Here's a sister with a couple of weeks left before harvest in a controlled environment with VPD in control.

ShroomKing said:

Let's hear what you think about VPD , or Vapor Pressure Differential , and it's importance to YOUR growing style. Do you follow it? Do you care? Has it changed your game? Let's hear it!

Everyone is entitled to their own opinions. Let's keep the heckling down to a minimum and keep our minds open.
View attachment 550838
Peace

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It means nothin.... stoma adapts to environment... i can show you tons of great plants that were grown in the red....veg and flower

Phew! Lookit those!!

Still waiting to see a vpd chart that was not designed for greenhouse lettuce,where bulky green water filled plants are my desired. Its like saying orchids and watermelons require the same environmental conditions to thrive.

That's a good observation. The exact same thing can be said of dive charts. They were devised using men, in a very certain age range and of a certain physical fitness. Also, IIRC, the BMI charts are similarly limited.