Vpd Survey

[Ina]

Humidifiers are very cheap and easy to run to increase RH.

O,really:)

 

[Monster762]

You'll find that trying to work in VPD optimums offers growth and plant health benefits. 40% RH is way too low unless you are in late flower and trying to prevent fungal pathogens. I hope I have clarified though that I'm a big fan of VPD. Its more a case that some growers misunderstand it a bit. The main thing really for less experienced growers to understand is that if you use the VPD chart it gives you a very good picture of where your RH should be relative to temp.

I can see what you’re saying
Usually I keep in there ( the vpd range) at about 55%
but I’m in deep red n seeing uptake and output more than I’ve ever seen within the “ range” and on clones I’ve ran in the range. So aside from it all. I learned exactly why what’s happening is happening

it’s outside the range n outside the box. If I’m right I’ll never chase vpd again.

 

[Glow]

Have you measured leaf surface temperature in this equation? Understanding the leaf surface and air temperature differential is important in VPD. This is what I mean by it being more complex than many growers think because there are numerous variables that need to be factored into the equation.

 

[Glow]

BTW I am also wondering if low humidity is helping with stretch which is why things look better. I.e. something I've written on this....
Running a lower humidity (approx. 50 %) during the stretch phase of the crop cycle (the first 2 – 4 weeks of the 12/12 light cycle, genetic dependent) can help a little in reducing stretch. Higher humidity (65 – 80%) causes more lavish growth with longer shoots and sometimes larger leaves. When the humidity is increased, plants stretch the main stem, shoots and petioles more. The cell elongation and hence the stretching of the entire crop depends on the cell pressure (Turgor pressure). In the event of low humidity, evaporation is high and the cell pressure of the crops is relatively low. This will slightly slow down the cell elongation reducing plant stretch. Under conditions with little evaporation (high humidity), the cell pressure is generally higher and more stretching can occur.

 

[Monster762]

Have you measured leaf surface temperature in this equation? Understanding the leaf surface and air temperature differential is important in VPD. This is what I mean by it being more complex than many growers think because there are numerous variables that need to be factored into the equation.

Ah no I haven’t done that my leaves are probably cooler than air. I got my rh to 40-45 now but just because I dropped temps like 4 degrees.
Idk I’m just trying to figure why my plants (which I’ve run clones from same mother same lights n all. ) are uptaking 3x as much as ever before but not burning. Actually demanding more. And that link told me why

 

[Glow]

Yeah its one misconception I've encountered recently when an advanced level grower came to me for consultancy and started ranting on about low EC and an aggressive VPD. I was what are you talking about man? Optimum EC really comes down to nutrient status and fertigation frequency with environmental factors such as RH and temp playing a much much lesser role. In fact studies show that certain nutrients such as iron are uptaken and found at higher levels in the plant tissue at high RH while other nutrients will be uptaken and present in the tissue at lower RH. So basically we are talking extremely complex biochemistry and plant physiology that a lot of growers might understand some of but miss other key parts of in understanding (resulting in incorrect assumptions).

 

[Glow]

Ah no I haven’t done that my leaves are probably cooler than air. I got my rh to 40-45 now but just because I dropped temps like 4 degrees.
Idk I’m just trying to figure why my plants (which I’ve run clones from same mother same lights n all. ) are uptaking 3x as much as ever before but not burning. Actually demanding more. And that link told me why

Probably worth doing. An infrared laser thermometer is a cheap item to purchase. I have got an article on the site about leaf surface temperature (LST) but again I don't like to link unless mods say it is okay although on the subject of VPD leaf surface temperature (i.e. canopy temp) is an incredibly important part of the process

 

[Monster762]

Yeah its one misconception I've encountered recently when an advanced level grower came to me for consultancy and started ranting on about low EC and an aggressive VPD. I was what are you talking about man? Optimum EC really comes down to nutrient status and fertigation frequency with environmental factors such as RH and temp playing a much much lesser role. In fact studies show that certain nutrients such as iron are uptaken and found at higher levels in the plant tissue at high RH while other nutrients will be uptaken and present in the tissue at lower RH. So basically we are talking extremely complex biochemistry and plant physiology that a lot of growers might understand some of but miss other key parts of in understanding (resulting in incorrect assumptions).

See we are talking complex and I think we’re talking misunderstood simply because everyone wants to quote some text book

Complex because of people making it that way.
Prime example look at math in school now. 20 steps in a circle to get the same answer we used to get in 2 steps when I was in school.
Now vpd and what I’m getting to.
I’m not gonna write a book unless someone really wants the rest of my theory. Maybe I’ll put it on my diary thread if someone wants to see it and exactly why I’m saying it. In action.

But main point vpd chart means nothing. It does give you an idea of where your highest transpiration rates are so in that form useful otherwise useless.
This is where it falls apart
Where everyone keeps digging too hard into an unproven science based on a book written by someone probably never grew a weed plant.
Facts in basic terms
We have a plant it wants to grow. It’s alive
living things need water period

If our air is stripped of water the plant is forced to hydrate itself other ways ( roots)
This causes more rapid uptake. More Rapid transpiration.
Also causes nutrients to be moved and used more rapidly.
Low rh starts showing with yellowing right? And crispy leaves Why is that? Yellow hm
Yellow = lack of or lock out of nutrients period. No other thing causes yellow. Whether ph is off or whatever
the lack of available nutrients to be uptaken is where the final fade and any stage plant yellowing comes from.
Now when rh is low
back to common sense
you are forcing the plant to draw from roots more. Leaching your nutes too. So you either end up yellow from demand of more inputs by the plant that done stripped your soil ( yeah that quick)
or crispy n burned n people calling it rh and windburn but it’s a flash nute burn in reality. Usually on less tolerant strains

From the rapid transpiration going on. From the low rh. There’s a lot more to it but my theory is based more on common sense. It’s as simple as people not thinking about cold contracts n hot expands.

But I think I’m in no hurry to try upping my rh. I’ll just stick to the full course meals regularly with tons of extra water to keep the yellow out n watch em explode.
I’ve never fed full strength. N saw burn at 75% before. On these same clones
Why the higher rh/ pressure you were talking about actually cuts transpiration slowing the flow building up.
With the low rh I’m throwing full strength with bloom booster calmag molasses all that every feed
Every day. And they suck it dry twice. In 4 gal pots. But now that I’m meeting thier crazy demands they are green again and I can see they been using the nutes like steroids

I think the chart is useful to an extent but I think you can go “ outside the box “ n actually get better results if you play it right.

 

[Glow]

Generally you find the research is accurate. Generally if someone is finding something anecdotally it is because something else is going on that are altering outcomes - its really that simple. I've been a grower for many many years while also studying plant physiology and starting my work career with a hort apprenticeship and almost without exception the research tends to prove very accurate. I've also been dealing with a broad cross section of growers for many many years and hear all sorts of weird and wonderful things:) Put it this way if you are getting optimum growth rates at 40% humidity you must be growing some sort of genetic freak of a cannabis plant because just about all experienced growers would tell you 40% RH is way too low based on hands on experience (and not research). Again you are talking complex biochemistry and in fact optimum nutrient partitioning occurs more efficiently at higher RH than lower RH in the case of many of the nutrient ions although others such as Ca and K will be better under low RH. I do see your logic but your logic doesn't match the data - that said, this doesn't make what you are saying as necessarily incorrect. It's more a case of what else is going on? Anyway, one thing I always say to people is each to their own. Its your crop and your yields so how you go about things is entirely up to you.

 

[3 balls]

See we are talking complex and I think we’re talking misunderstood simply because everyone wants to quote some text book

Complex because of people making it that way.
Prime example look at math in school now. 20 steps in a circle to get the same answer we used to get in 2 steps when I was in school.
Now vpd and what I’m getting to.
I’m not gonna write a book unless someone really wants the rest of my theory. Maybe I’ll put it on my diary thread if someone wants to see it and exactly why I’m saying it. In action.

But main point vpd chart means nothing. It does give you an idea of where your highest transpiration rates are so in that form useful otherwise useless.
This is where it falls apart
Where everyone keeps digging too hard into an unproven science based on a book written by someone probably never grew a weed plant.
Facts in basic terms
We have a plant it wants to grow. It’s alive
living things need water period

If our air is stripped of water the plant is forced to hydrate itself other ways ( roots)
This causes more rapid uptake. More Rapid transpiration.
Also causes nutrients to be moved and used more rapidly.
Low rh starts showing with yellowing right? And crispy leaves Why is that? Yellow hm
Yellow = lack of or lock out of nutrients period. No other thing causes yellow. Whether ph is off or whatever
the lack of available nutrients to be uptaken is where the final fade and any stage plant yellowing comes from.
Now when rh is low
back to common sense
you are forcing the plant to draw from roots more. Leaching your nutes too. So you either end up yellow from demand of more inputs by the plant that done stripped your soil ( yeah that quick)
or crispy n burned n people calling it rh and windburn but it’s a flash nute burn in reality. Usually on less tolerant strains

From the rapid transpiration going on. From the low rh. There’s a lot more to it but my theory is based more on common sense. It’s as simple as people not thinking about cold contracts n hot expands.

But I think I’m in no hurry to try upping my rh. I’ll just stick to the full course meals regularly with tons of extra water to keep the yellow out n watch em explode.
I’ve never fed full strength. N saw burn at 75% before. On these same clones
Why the higher rh/ pressure you were talking about actually cuts transpiration slowing the flow building up.
With the low rh I’m throwing full strength with bloom booster calmag molasses all that every feed
Every day. And they suck it dry twice. In 4 gal pots. But now that I’m meeting thier crazy demands they are green again and I can see they been using the nutes like steroids

I think the chart is useful to an extent but I think you can go “ outside the box “ n actually get better results if you play it right.

I have a buddy that gets consistent good results by doing just about everything "outside the box", only because he's never read a book or done any research, I swear to god some people are just lucky. I'm on the other end of the spectrum, constantly researching and experimenting. I like to wick as much wisdom as I can from the scientific types with their research and the outlaw OG types with their years of hands on trial and error, thus I'm perpetually changing 6 things at a time, never knowing for sure what's what.:)
That being said, I'm wondering if you are seeing the benefits of feeding at full strength more than anything. I follow the reasoning of many that I respect, that the nutrient companies want you to use as much product as possible but I tend to side with the fact that if they prescribe anything other than the proper dose, your results will steer you away.

Of course, as always, there are infinite variables in this game, just throwing it out there.

 

[MIMedGrower]

This is all very interesting. For 30 years growers have done things one way pretty much like the old grow books advised.

Metal halide for blue in veg hps in flower for more red.

High humidity for clones, seedlings and young plants through veg. Lowering humodity for flower.

Now we have many more growers and businesses throwing their experience and research in the pool.

Why are the same debates still going on as decades ago about growing weed while every othwr kind of farmer has specific nute ratios and parameters to follow on any agriculture info?

Its because weed gets you high and thats when weed growers start thinking about their job. ;-)


That said. If you look into different cultivars like say roses or lettuce you will see that the grower uses different techniques, parameters and nute ratios for the different sort of crop.

Lettuce is to harvest leafy greens but roses only the stem and flowers. They need different light spectrum, envirenment and nutrients to give best potential.

Well we grow for flowers. But our plant grows a leafy structure in veg. So tech like vpd and full spectrum lighting with a good balance of blue will grow the best leafy compact plants.

But in flower we want a safer envirenment for mold so lower humidity. We want lower temps to preserve potency and flavor. And we want more red light to spur branching and flower set and bloom.

So there is no answer that makes any tool or technique automatically correct.

why are these discussions always one side or the other?

Our plant has multiple different stages and it aint lettuce. :-)

 

[Glow]

I think where nutrient strengths are concerned it comes down to 1) whether you are recycling or growing RTW/DTW. For recycling growers who purchase off the shelf formulas and don't lab analyse and correct for specific ions they need to run higher strengths (EC) so at that point luxury feeding is a must because there is a preferential removal of some nutrients over others and some nutrients become depleted in solution while others accumulate - so at that point running high strengths as per feed charts is perhaps necessary. But in RTW/DTW where fresh solution is fed at every feed most charts recommend too high ECs. 2) fertigation frequency inline to nutrient status is all important in determining optimum EC because higher numbers of fertigations per day will mean you can run a far lower EC than say 1 fertigation per day in RTW/DTW etc. So the point being when you talk about optimum EC you must factor in the growing methodology as key in the equation. Definitely though some nutrient manufacturers make insane recommendations with regards to EC (ml/gal ml/L) for a lot of growing methodologies.

 

[Glow]

This is all very interesting. For 30 years growers have done things one way pretty much like the old grow books advised.

Metal halide for blue in veg hps in flower for more red.

High humidity for clones, seedlings and young plants through veg. Lowering humodity for flower.

Now we have many more growers and businesses throwing their experience and research in the pool.

Why are the same debates still going on as decades ago about growing weed while every othwr kind of farmer has specific nute ratios and parameters to follow on any agriculture info?

Its because weed gets you high and thats when weed growers start thinking about their job. ;-)


That said. If you look into different cultivars like say roses or lettuce you will see that the grower uses different techniques, parameters and nute ratios for the different sort of crop.

Lettuce is to harvest leafy greens but roses only the stem and flowers. They need different light spectrum, envirenment and nutrients to give best potential.

Well we grow for flowers. But our plant grows a leafy structure in veg. So tech like vpd and full spectrum lighting with a good balance of blue will grow the best leafy compact plants.

But in flower we want a safer envirenment for mold so lower humidity. We want lower temps to preserve potency and flavor. And we want more red light to spur branching and flower set and bloom.

So there is no answer that makes any tool or technique automatically correct.

why are these discussions always one side or the other?

Our plant has multiple different stages and it aint lettuce. :)

Absolutely but also when people talk VPD this is also spoken about in many cases. That is, it is desirable to not run what is considered optimal VPD when considering other factors such as young veg plants (which want high RH) and developing flowers and mould (where you want to run very low RH of 40 - 45% RH). Also and one reason I say VPD is misunderstood by a lot of growers is that you need to consider why scientists look at VPD and this for the most part is to evaluate water status relative to stomatal conductance and growth rates. Most of these studies are also done in soil in either greenhouse or outdoor crops so firstly it is important to disseminate information from what were the scientists looking at and what were the parameters of the study?

In hydroponics we aren't nearly as concerned about water use and wilting points etc as are outdoor growers for instance. I think what happens too often is people misinterpret the data and don't stop to think yes but all good and well but what is the point of this in my situation? So it's important to step back a bit from research and evaluate what the parameters of the study were.

Just quickly though on the subject of MH and HPS - there's no doubt indoor lighting is on the change with better and improved lighting technologies which are developed for optimised crop growth beginning to emerge. So just because growers have done it for years doesn't make it the best way - more a case of it being what was available at the time. And that's the thing about science; it enables us to evolve and improve things.

Also mate, a lot of the old grow books aren't so good. By following their info you'd be losing yield when compared to growing using cutting edge technologies. The Med scene is like any other. It had to start somewhere. It's been evolving ever since.

 

[Glow]

Hey BTW guys (and gals I.e. sincity) just want to say I find the farm has a really nice vibe. People are really friendly and trying to help and be nice to one another. It makes a big change from just one or two forums I've been to where they are riddled with haters and trolls. Well done THC Farmer. Good crew and presumably good moderation. I've really enjoyed the conversation.

 

[Monster762]

I think where nutrient strengths are concerned it comes down to 1) whether you are recycling or growing RTW/DTW. For recycling growers who purchase off the shelf formulas and don't lab analyse and correct for specific ions they need to run higher strengths (EC) so at that point luxury feeding is a must because there is a preferential removal of some nutrients over others and some nutrients become depleted in solution while others accumulate - so at that point running high strengths as per feed charts is perhaps necessary. But in RTW/DTW where fresh solution is fed at every feed most charts recommend too high ECs. 2) fertigation frequency inline to nutrient status is all important in determining optimum EC because higher numbers of fertigations per day will mean you can run a far lower EC than say 1 fertigation per day in RTW/DTW etc. So the point being when you talk about optimum EC you must factor in the growing methodology as key in the equation. Definitely though some nutrient manufacturers make insane recommendations with regards to EC (ml/gal ml/L) for a lot of growing methodologies.

This sounds right and again proves my point. That inside or outside if vpd range you can still get good results by altering the inputs. N not just nutes. Amount frequency all that like you said. It explains why I’m ok at 40% when like your own words said “every grower” going by the book will say I’m wrong. I’m saying they are all wrong. N my wall of bud proves it. Along with the small print in everything everyone is saying here. It’s like we agree yet disagree. How they say in the movie blow ? Chasing the wrong dream. That’s where it’s going wrong
It does not say you will only get great results in this range. It gives you a dummy range where you can slip more on everything else in the grow but 100 degree temps can be utilized. So can 50.

In relation to vpd ( or I’ll say common sense ) if air is full of water it’s harder to transpire. Take a rag n breath through it. Wet the same rag n try again. My point proven again.

Low rh even extremely low can be adjusted to on other parts of the grow to actually beat those numbers inside the vpd range in transpiration rates. Dryer air is what opens the gate. Does this add up yet?
Idk I’m no scientist but also no dummy and I just can’t stop it from smacking me in the face. Oh and my humidity broke 40. And guess what the cost was?
Only needed one feed yesterday. When in 30s rh they took 2 like a champ n still felt like styrofoam after 12 hrs in the dark. Uptake dropped soon as rh went up. Explain that one.i can again with common sense

Cause closer to the 50% or over stops the plants ability to transpire

Soon as you near the even ground the rates drop. Period.
Look at clones in humidity dome. As long as humid they droop Soon as they start to dry they pray

 

[Glow]

I think you'd have a very hard time selling your "It explains why I’m ok at 40% when like your own words said “every grower” going by the book will say I’m wrong. I’m saying they are all wrong." point to the grow community mate but as I say each to their own:)

Oh and I think you're trying to prove yourself right over others but I think you'll be disappointed because others will simply agree to disagree.

 

[MIMedGrower]

Absolutely but also when people talk VPD this is also spoken about in many cases. That is, it is desirable to not run what is considered optimal VPD when considering other factors such as young veg plants (which want high RH) and developing flowers and mould (where you want to run very low RH of 40 - 45% RH). Also and one reason I say VPD is misunderstood by a lot of growers is that you need to consider why scientists look at VPD and this for the most part is to evaluate water status relative to stomatal conductance and growth rates. Most of these studies are also done in soil in either greenhouse or outdoor crops so firstly it is important to disseminate information from what were the scientists looking at and what were the parameters of the study?

In hydroponics we aren't nearly as concerned about water use and wilting points etc as are outdoor growers for instance. I think what happens too often is people misinterpret the data and don't stop to think yes but all good and well but what is the point of this in my situation? So it's important to step back a bit from research and evaluate what the parameters of the study were.

Just quickly though on the subject of MH and HPS - there's no doubt indoor lighting is on the change with better and improved lighting technologies which are developed for optimised crop growth beginning to emerge. So just because growers have done it for years doesn't make it the best way - more a case of it being what was available at the time. And that's the thing about science; it enables us to evolve and improve things.

Also mate, a lot of the old grow books aren't so good. By following their info you'd be losing yield when compared to growing using cutting edge technologies. The Med scene is like any other. It had to start somewhere. It's been evolving ever since.

So it would seem we agree. Vpd is a tool just like light spectrum, leaching and as you brought up here nutrients.

The university of michigan is testing discrete colored diodes and plant growth now. Full spectrum led is not the future. Specific diodes set up in a spectrum for individual crops is the goal.

Bet we are leas than 5 years away from indoor tomato specific lighting to get grandmas flavor into the supermarket.

And then maybe a real weed lamp.

 

[Glow]

I think one thing many growers miss is that a plant's genetic potential evolved under certain conditions. So for example cannabis evolved under the sun (not HPS or MH lighting) which provides a very broad spectrum at differing levels and ratios. It also evolved during the Mid-Palaeozoic era at high CO2 (1500–3000 ppm) before the beginning of a period of low CO2 (<1000 ppm) we are in today so if you want your crop to achieve genetic potential it is imperative to produce under light that is very similar if not identical to the sun re spectral output and under high CO2 (i.e. CO2 enrichment).

All I can say about LED is to date it has been very disappointing but its an evolving technology so perhaps one day they will get it right (perhaps not). However, if you want to achieve optimum yields give LED a miss for now.

 

[MIMedGrower]

I think one thing many growers miss is that a plant's genetic potential evolved under certain conditions. So for example cannabis evolved under the sun (not HPS or MH lighting) which provides a very broad spectrum at differing levels and ratios. It also evolved during the Mid-Palaeozoic era at high CO2 (1500–3000 ppm) before the beginning of a period of low CO2 (<1000 ppm) we are in today so if you want your crop to achieve genetic potential it is imperative to produce under light that is very similar if not identical to the sun re spectral output and under high CO2 (i.e. CO2 enrichment).

All I can say about LED is to date it has been very disappointing but its an evolving technology so perhaps one day they will get it right (perhaps not). However, if you want to achieve optimum yields give LED a miss for now.

Ok. This is an interesting point. However our indoor cultivars have been bred under hps for 40 years.

Will the highest potential maybe be with the breeders parameters?

 

[Monster762]

Ok. This is an interesting point. However our indoor cultivars have been bred under hps for 40 years.

Will the highest potential maybe be with the breeders parameters?

Yes it should if the breeder nailed the parameters before breeding.