Is VPD important?

[CultivationArt]

after a while everyone i know who is a decent grower is the same

Ouch. I care about those things and been at it well over a decade. Grain of salt I guess lol

 

[Roy Growin]

Ouch. I care about those things and been at it well over a decade. Grain of salt I guess lol

Not rattling your cage, but I would agree with @bluter
Most of that techie stuff, charts etc are feckin useless and apply to nobody
Most of the noob problems we see here are folks blindly following charts, meter readings and UTube vids and forgetting to actually observe their plants, then turn up here with a dead plant and ask for help
I sincerely hope that is not offensive to anybody

 

[bluter]

Ouch. I care about those things and been at it well over a decade. Grain of salt I guess lol

it's not a knock. don't take it that way.

and it's nothing against your grow style at all.

all vpd does is tell you to adjust heat and rh. that's it. that's all you can manipulate anyway under most circumstances.

there's a very limited number of ways to do that. it's what we've been all doing to help our grow spaces along from the very beginning. long before the charts.

if you look at what most folk are suggesting for temps and rh etc, you will see it lines up with most of those charts.

the only difference is grow style - i look at the plants. if they look happy i don't give a damn.

i'll check temps / rh etc to make sure it is within reason, if it is great. if it isn't i'll make small changes to correct. but i won't stress. there's only so much i can do. - that is the key. you aren't god.

if the plants crash i'll stress. but generally i know something is coming well before that and make corrections. in practice i work with the seasons and the environmental changes it brings to the house.

 

[CultivationArt]

Reading your plants is 90% of the charts I use. If you can’t read your plants. Wtf are you using a chart for. Idk. I guess my point is I use the charts to adjust my numbers. Heat vs humidity at different stages of growth. I just learned about it after a decade of growing. So I guess call me a newb. I don’t wanna take offense to that remark. But thru text. Shits always mixes up. And it just seemed like that was directed to my style of growing was amateur. Kinda stung lol. But I take corrective criticism very well. And a way of filtering out the honest from liars.


Kinda the reason I joined this community is nobody seemed to pass judgment on people. Other places can be cruel for those just looking for some good friends to grow and share the day with.

 

[The70’s]

Being that im setting up for my first grow in the fall, im throwing all the questions i can out at you guys and gals. Once i get the feeling that enough people agree i set the issue aside and move on to the next question. Im quite satisfied with all of your input as to this VPD issue.

I have an Xtra 4” inline fan, what are your thoughts on fan on the input, and filtered attached fan output ?

Im an Audio/Video guy at heart and people can waste tons of money, and do, on expensive cables, speaker wire and power cords. Its all snake oil if you ask me…… but the novice wants to cross all his/her T’s and Dot the i’s…..

My grow space is really taking shape, because of all the good advice here, just dont go buying $2,000 HDMI cables hahaha

 

[The70’s]

I have to say over watering seems to be an issue with us new folks who grow in soil or coco too………..

 

[Skunksta]

I have to say over watering seems to be an issue with us new folks who grow in soil or coco too………..

Can’t really over water coco. Maybe water to frequent. Pass 20L though it as long as it’s once a day twice if your ladies are asking for it.

 

[TorturedSoul]

I have an Xtra 4” inline fan, what are your thoughts on fan on the input, and filtered attached fan output ?

I'd never put a fan on an intake vent unless I had a setup in which I had to run an intake hose out, over, down, left, back around, down some more... But for a simple setup that doesn't need to draw air directly from a distant location, I have always done passive intake / active exhaust. Helps ensure that everything leaves through that exhaust, and keeps a negative pressure in the garden. If I'm not able to move an adequate amount of air that way, it'll be because I used a wimpy (or the wrong type of) exhaust fan that cannot handle the carbon filter restriction.

Heh... There is no extra fan - there is only short one tent, carbon filter, whopping great light, and plants. But the correct number of fans, ha ha ha. If budgets were merely suggestions .

Can’t really over water coco.

With any non-soil hydroponic type media, "over watered" = "not enough air in the root zone," that's why DWC (deep water culture) works so well - the plant's root system is actually submerged in water (nutrient solution), but there is enough active aeration to ensure access to O₂. The coco allows for oxygenation. It's not going to be as good as an actively-aerated setup (at least in theory), but it's better in that regard than soil, or should be.

 

[Skunksta]

I'd never put a fan on an intake vent unless I had a setup in which I had to run an intake hose out, over, down, left, back around, down some more... But for a simple setup that doesn't need to draw air directly from a distant location, I have always done passive intake / active exhaust. Helps ensure that everything leaves through that exhaust, and keeps a negative pressure in the garden. If I'm not able to move an adequate amount of air that way, it'll be because I used a wimpy (or the wrong type of) exhaust fan that cannot handle the carbon filter restriction.

Heh... There is no extra fan - there is only short one tent, carbon filter, whopping great light, and plants. But the correct number of fans, ha ha ha. If budgets were merely suggestions .



With any non-soil hydroponic type media, "over watered" = "not enough air in the root zone," that's why DWC (deep water culture) works so well - the plant's root system is actually submerged in water (nutrient solution), but there is enough active aeration to ensure access to O₂. The coco allows for oxygenation. It's not going to be as good as an actively-aerated setup (at least in theory), but it's better in that regard than soil, or should be.

Light bleed keep a hole open is one issue.
also as you said negative pressure how many tents zip have broken due to that.
Also as you know what works in your house wont in mine.
Its why i always say its what works for me.
and again as its all i grow in what works for me.
Is that i have NEVER over watered coco.

 

[TorturedSoul]

Light bleed keep a hole open is one issue.

I suppose, if you don't have any kind of light trap.

negative pressure how many tents zip have broken due to that.

None?

Also as you know what works in your house wont in mine.

I can't really respond to that, because I am unsure what, exactly, you are referring to. Using an adequate exhaust fan? Not sticking a fan in one of the intakes? It might have been obvious if I wasn't 7/8ths asleep, but I missed a night's worth last night. and am on the way to go not repeat the experience, lol.

 

[Delps8]

This site is a good source of information.

 

[Skunksta]

In MY space it was a former walk-in wardrobe
With sliding doors.
No way to get fresh air really the tent fits snug to the wall. Hence MY need for an intake fan. Do I run it in winter not really in summer all the time.
Other wise MY RH would hit silly level
Also the heat. So for ME an intake fan is a must.
In my small bedroom i work in.
You may well have loads of space.
But as I have said what works for you might not for me.
Also my fans are 6 inch both ways and controlled far from weak.

 

[Buds Buddy]

I'd say a lot of his VPD concerns would be based on the area he lives in. Whether Hot & Dry climate or Cool & Wet. Also on the type of lights he's running. I think the VPD charts are designed for HPS lighting & not so much for LED's.
If you were to look at my 2 current grows you would see I dialed everything in at 77F & 65% RH in one of the journals. Plants grew at a snails pace. I removed my AC & let temps go up in the 80's with 25% - 35% RH & the plants doubled in size in less then 2 weeks. In my other grow I didn't dial anything in right from the beginning & those plants are growing like fire. The only time I worry about VPD being kind of close is about 1/2 way through flower as I don't want too high of RH because of the possibility of WPM or Mold. I also prefer to lower my temps to about 70F the last couple weeks to increase trichome production & bring out some color. So my thought is, VPD isn't real important until the end of flower.

 

[Delps8]

I'd say a lot of his VPD concerns would be based on the area he lives in. Whether Hot & Dry climate or Cool & Wet. Also on the type of lights he's running. I think the VPD charts are designed for HPS lighting & not so much for LED's.

Vapor pressure deficit has nothing to do with lighting. Read through the paper from Pulse - it's a good explanation.

If you were to look at my 2 current grows you would see I dialed everything in at 77F & 65% RH in one of the journals. Plants grew at a snails pace. I removed my AC & let temps go up in the 80's with 25% - 35% RH & the plants doubled in size in less then 2 weeks. In my other grow I didn't dial anything in right from the beginning & those plants are growing like fire. The only time I worry about VPD being kind of close is about 1/2 way through flower as I don't want too high of RH because of the possibility of WPM or Mold. I also prefer to lower my temps to about 70F the last couple weeks to increase trichome production & bring out some color. So my thought is, VPD isn't real important until the end of flower.

I have no reason to doubt that what you're saying is true. What you and I believe or experience does not change the fact that that temperature and humidity have immediate, direct, and measurable impacts on how plants grow. Vapor Pressure Deficit gives us a number that covers a variety to combination of temperature and humidity values in which plants will tend to grow well…or not so well.

Here in the US, we have a variety of climates. The Southeast has high humidity and can hit very high temperatures. I call it "80 and 80". I don't care for that climate. Go west of the Mississippi River and RH starts to drop. We get climates like the desert southwest where temperatures are even higher but RH plummets. A simple experiment to see how temperature and humidity can impact plants would be to swap some plants between the Louisiana bayou and the desert in Arizona. Do that and you're going to have dead plants in a hurry. Take a herd of armadillos from Texas and move them to Barrow Alaska for the winter and we'll see how well they do. The undeniable truth is that, setting aside human beings, living things can only exist in a very narrow set of conditions. VPD is number that describes the the combinations of temperature and RH values under which plants will tend to grow well.

The VPD values for cannabis are 0.8 seedling stage, 1.0 in veg, and 1.2 in flower. Obviously, the cannabis grows in temperature and RH conditions other than those but that does not take away from the fact that, under those values of temperature and humidity, the plant will tend to do better than if it is not grow in those combinations of temperature and humidity.

The reason why I use VPD is that temperature and RH are two of the factors that a comprise the grow environment. The graphic that I've attached (it's a screenshot from one of the videos by Dr Bugbee) and it's a good roadmap to having a successful grow. VPD is not magic and there's no mystery to it. It's a piece of the "growing equation" and, by controlling all of the variables, you will be successful in growing whatever you're growing.

 

[Buds Buddy]

Vapor pressure deficit has nothing to do with lighting. Read through the paper from Pulse - it's a good explanation.


I have no reason to doubt that what you're saying is true. What you and I believe or experience does not change the fact that that temperature and humidity have immediate, direct, and measurable impacts on how plants grow. Vapor Pressure Deficit gives us a number that covers a variety to combination of temperature and humidity values in which plants will tend to grow well…or not so well.

Here in the US, we have a variety of climates. The Southeast has high humidity and can hit very high temperatures. I call it "80 and 80". I don't care for that climate. Go west of the Mississippi River and RH starts to drop. We get climates like the desert southwest where temperatures are even higher but RH plummets. A simple experiment to see how temperature and humidity can impact plants would be to swap some plants between the Louisiana bayou and the desert in Arizona. Do that and you're going to have dead plants in a hurry. Take a herd of armadillos from Texas and move them to Barrow Alaska for the winter and we'll see how well they do. The undeniable truth is that, setting aside human beings, living things can only exist in a very narrow set of conditions. VPD is number that describes the the combinations of temperature and RH values under which plants will tend to grow well.

The VPD values for cannabis are 0.8 seedling stage, 1.0 in veg, and 1.2 in flower. Obviously, the cannabis grows in temperature and RH conditions other than those but that does not take away from the fact that, under those values of temperature and humidity, the plant will tend to do better than if it is not grow in those combinations of temperature and humidity.

The reason why I use VPD is that temperature and RH are two of the factors that a comprise the grow environment. The graphic that I've attached (it's a screenshot from one of the videos by Dr Bugbee) and it's a good roadmap to having a successful grow. VPD is not magic and there's no mystery to it. It's a piece of the "growing equation" and, by controlling all of the variables, you will be successful in growing whatever you're growing.

Been there, tried all that. Been growing for 5 years now. I had everything Automated (RH, AC, Intake & Exhaust, Humidifier & Dehumidifier, etc.) using a Saturn 4. Temps constantly at 77F & RH of 65%. My plants grew very, very slowly. With the higher temps & lower RH they grow really fast. I believe it's more the Leaf Surface Temp that matters. I think at a tent temp of 84F you get a leaf temp of 77F when using LED's. This is where the difference in HPS & LED vary when it comes to VPD as an HPS will give you a hotter leaf surface temp with a grow room of 84F at the same PAR level because they put off more heat than LED's. This is why I think the VPD charts were designed for HPS.

 

[Skunksta]

Personally I think it’s a ruff guild and spending so much time and money in some cases to get
Things spot on causes more issues than the avg
Grower needs. Humidifier dehumidifiers aircon
Units etc. but each to there own. I guess

 

[Delps8]

Been there, tried all that. Been growing for 5 years now. I had everything Automated (RH, AC, Intake & Exhaust, Humidifier & Dehumidifier, etc.) using a Saturn 4. Temps constantly at 77F & RH of 65%. My plants grew very, very slowly. With the higher temps & lower RH they grow really fast. I believe it's more the Leaf Surface Temp that matters. I think at a tent temp of 84F you get a leaf temp of 77F when using LED's. This is where the difference in HPS & LED vary when it comes to VPD as an HPS will give you a hotter leaf surface temp with a grow room of 84F at the same PAR level because they put off more heat than LED's. This is why I think the VPD charts were designed for HPS.

"This is why I think the VPD charts were designed for HPS." - Ok, now I understand why you're thinking that.

The type of lighting that's used will directly impact temperature and temperature is a key component of VPD but light source is not in the equation used to calculate VPD.

Where light source comes in to play is that HPS tends to heat things up whereas LED's don't. And, yes, plants tend to grow faster in warmer environments than in environments that are not as warm, all other things being equal. When switching from HPS to LED, growers are advised to boost ambient temps by 10° to compensate.

Leaf surface temperature is an important factor in calculating VPD, so important that you cannot calculate VPD without it which is why it's part of the discussion on the page at the link. When you look at the VPD chart, there are only two things to do - click the stage of growth and enter the leaf surface temperature offset.

VPD is only a guide and temperature and humidity are only two of the nine parts of the growing environment. The value of using VPD is that it indicates combinations of temp and RH that will tend to give better results than if plants are grown outside of those temperature and RH combinations.

 

[LKABudMan]

I think VPD is a very useful tool for growing. However I don't think that you can dial it in based on a chart. It's also important to know the leaf temperature as it can be quite different than the ambient temperature, especially with different light sources.

On my first grow I left the humidifier in the tent at 65% based on the charts. After three weeks I couldn't figure out why the plants were struggling. I decided to measure my leaf temperatures and realized that with the LEDs my leaf temperatures were several degrees below my measured ambient. I lowered the RH down to 55% and they took off.

Buds, is it possible that by measuring VPD based on the ambient temperature your missing the sweet spot? If your leaf temperature are a few degrees below your ambient your VPDs could be < 1.0.

I believe there's a sweet spot where temperature and humidity is balanced to allow for optimal plant respiration (ie. perfect VPD). I also believe that sweet spot changes as a plant goes through stages of development. I don't always hit the VPD I am shooting for, but I keep shooting anyways

 

[bluter]

The type of lighting that's used will directly impact temperature and temperature is a key component of VPD but light source is not in the equation used to calculate VPD.


Where light source comes in to play is that HPS tends to heat things up whereas LED's don't.

hps and led light are very much different. led burn can take the form of a genetic looking malformation. led photons can damage cell structure in developing leaves, in the absence of heat. hps typically creates a heat burn before that happens. both can bleach a plant.

When switching from HPS to LED, growers are advised to boost ambient temps by 10° to compensate.

i wouldn't necessarily recommend that. 18 - 26c is pretty much optimum if you can maintain it. most will cite that range for flower, but it's a good all around temp range.

there is a +/-- of 4c where things will still be ok, but growing or development may be affected. things get super problematic if you start getting outside of that. it's also true they like it a little warmer in veg and a little cooler in flower. which runs counter to how most grow spaces move, but that's what we deal with.

i personally try to maintain it in the 22 - 24c range, but usually wind up a degree or two higher.

Leaf surface temperature is an important factor in calculating VPD, so important that you cannot calculate VPD without it which is why it's part of the discussion on the page at the link. When you look at the VPD chart, there are only two things to do - click the stage of growth and enter the leaf surface temperature offset.

you are dead on correct. most don't take leaf temps, and go by ambient room temp. it can also be an issue with led, as led can cause damage in the absence of heat.

 

[CultivationArt]

Plants grow off the 9 cardinal points. Balance. Increase light. Increase everything else.

Vpd has to deal with how the plant effectively breaths in its climate and uptakes water and nutrients. That’s 4 cardinals out the 9.

Leaf surface temperatures are the ones that directly affect that plant. Like putting your hand under a hps back in the day. Not ambient. However not to say ambient is not important. It’s very important

The people claiming plants grew faster out the sweet spot. Was because your sweet spot was to cold to begin with. 84-86 seems to be the sweet ambient spot with a lst of 77-80. Under led. I just personally noticed a jump in how many shoots took dominance right away to start early training. Idk. I was told by a buddy of mine. Whom is very reputable in my books. Said imagine using a high elevation mask all the time. That’s how a plant feels outta range. Kinda made me feel bad lmao