Vapor Pressure Deficit - VPD and Nutrient Deficiency

the gnome · Dec 29, 2013

Kcar said:
Watch your PH as the Pro-tect and raise it significantly...
Also, what medium are your growing in?

yeah, i like the protek raising Ph,
after adding nutes which usually drop Ph,
I'm many times on the money instead of 5.6 5.8

papaduc said:
Gnome, chances are mate it's a simple case of overfert and backing off on the nutes is what's helped you more than anything.

The leaf curl you showed in that link is typical of low humidity, but the picture above looks like nothing more than a little bit of burn. If you've predicted a bigger draw on nutes because of the increased Co2 and have fed accordingly, and with silica in the mix, I'm 100% sure that's all it is.

That's got nothing directly to do with high VPD, but a knock on effect of it is the higher ec makes the tissue of the foliage more susceptible to burning at higher temps and lower rh.

well at 1st it was over feeding a *bit* too much but not near enough to get nute burn on the leaves.
ive been doing this a while.
the nutes wern't being taken in because the plants were not transpiring. as in--->VPD
so i backed off to water and liquid karma only, it helped a lot but still the prob was there just not that big of an issue
Rh at this time was 55% and only 1 strain thats pictured was the worst,

when i fired up the 6th 1000w lamp 5-7 days later RH dropped to mid 40s, and everything started being affected and the strain pictured started getting solid yellow like kcars pics on post#1
and i was still feeding water and LK, this is the damage your seeing in the pic now.
in the last 3 days Ive raised Rh to bounce between 65% and 75%.
all the probs went away and overnite i a saw a huge difference for the better.
so there is definitely a direct cause and effect between Rh and the probs Ive been having in my case.

papaduc · Dec 29, 2013

Coconutz said:
Papaduc, I dont think you are seeing the connection between VPD and uptake.
Low humidity, or low vpd? A low humidity(45%) isnt going to cause that kind of damage in a cool room... But it will in a hot room with intense lighting and co2...
While his nutes may have been high for his conditions they probably wouldnt have been high under better conditions and may not have ended up burning his plants.
He already knows his plants are burned... What he is saying is he believes its related to the conditions of the room and I agree 100% because Ive never seen plants burn like that without an EC over 2.0 or some sort of problem with the environment or grower error.
Gnome seems like a competent gardener and is probably on the right path to correcting the issue.
It seems like each one of your posts neglects key issues regarding VPD.
Have you read any of the articles being linked in the threads?
Im not trying to bust your balls man, it just seems like you should at least reread the material to have a better understanding of VPD.

I totally understand the effect of a pressure deficit and how it affects uptake of water from the roots. I don't know what's giving you the impression that I don't.

Your observation that plants seldom burn unless the EC goes above 2.0, goes against everything I have experienced. My EC rarely goes above 1.0 from a background of 0.2. If I go above 1.2, especially on picky strains, I might see signs of toxicity in the plants.

The things is, with a high pressure deficit, or very low humidity, the plant transpires, and when what it is drawing from is a high EC, you will see this kind of damage.

I totally understand how any potential damage caused by higher EC values is exacerbated by low eh or high VPD, essentially they are the same thing when related to the mechanism of transportation of water from the roots to the foliage and out into the atmosphere.

I have never once insinuated that Gnome doesn't know full well what he's doing. I know he does. But none of us get everything right every step of the way and if the fella just drops back his EC, he'll counter balance the envirnmental issues causing what would otherwise - as you say - be a fine EC to run.

If you step back, you can see I actually am not disagreeing with anything you say. Whether you want to refer to it as high VPD or low RH, it's up to you. But the basic issue it creates is essentially the same in this respect.

Also, the initial pictures in this thread - those stark yellow lines and bleached pale leaves, are not the same as those on the plants Gnome posted. I stand by what I said about VPD not being the cause of that.

the gnome · Dec 29, 2013

coconutz what your saying I agree with 100%

we were posting at the same time.. i'm just a slow as typer

papaduc · Dec 29, 2013

Sorry, but just to add, I suppose an easier way to put into context what I'm saying is this: We run our plants to suit our environment. We watch them and read them and on one attic run in the summer, we might see completely different levels of everything being used up by the plants, compared to a winter grow in a shed. It's why I questioned recently the use of spreadsheets and data collation vs the hands on aspect of reading and understanding the plants. The idea that even clones grow the same from one situation to the next is a flawed one.

In this respect, I fully agree with you that environmental variables dictate that what is/was ok in one setup, is not in another. There's nothing about that which I disagree with.

In this instance I'm not saying Gnome is running an EC which is too high, or that he doesn't know his plants very well in fact, but that the issue with those particular plants is that, for whatever reason, they're not tolerating the higher ec. Like you say, in this case it's because of C02 high temps etc. But nevertheless, it's the same problem fundamentally.

Either way Gnome, I think you'll get it fixed. It does just look like a case of burn which has been brought on by you adjusting to and understanding a new environment, just as your plants must do. I know for a fact that if I started running sealed rooms on C02, I'd be having the same problems dialing it all in. You'll be on it soon fella, fine tuning it no doubt.

Coconutz · Dec 29, 2013

the gnome said:
yeah, i like the protek raising Ph,
after adding nutes which usually drop Ph,
I'm many times on the money instead of 5.6 5.8

well at 1st it was over feeding a *bit* too much but not near enough to get nute burn on the leaves.
ive been doing this a while.
the nutes wern't being taken in because the plants were not transpiring. as in--->VPD
so i backed off to water and liquid karma only, it helped a lot but still the prob was there just not that big of an issue
Rh at this time was 55% and only 1 strain thats pictured was the worst,

when i fired up the 6th 1000w lamp 5-7 days later RH dropped to mid 40s, and everything started being affected and the strain pictured started getting solid yellow like kcars pics on post#1
and i was still feeding water and LK, this is the damage your seeing in the pic now.
in the last 3 days Ive raised Rh to bounce between 65% and 75%.
all the probs went away and overnite i a saw a huge difference for the better.
so there is definitely a direct cause and effect between Rh and the probs Ive been having in my case.

Did you drop your base nute for 5-7 days also?
That would yellow my plants in 2 days or less. Especially in my flower room

papaduc · Dec 29, 2013

the gnome said:
so there is definitely a direct cause and effect between Rh and the probs Ive been having in my case.

I don't doubt there is, Gnome. Humidity and temps will have a bearing on everything else. Like I say, they can exacerbate a problem, or create one where there wouldn't otherwise have been one. But I've grown in 32c heat and sub-30% humidity, and not had those same problems.

The difference in your case is Co2, not the actual relative humidity/heat. I'm not the one to give you any advise on running sealed rooms with Co2, but what I can say for sure is plants can do very well on very low humidity and high temps. It's not an ideal scenario, but in my own experience it has never caused me those problems.

I know people with experience of running sealed, co2-enriched rooms will be able to give you more help with your situation than I can offer. All the best :tiphat:

the gnome · Dec 29, 2013

papaduc said:
I don't doubt there is, Gnome. Humidity and temps will have a bearing on everything else. Like I say, they can exacerbate a problem, or create one where there wouldn't otherwise have been one. But I've grown in 32c heat and sub-30% humidity, and not had those same problems.

The difference in your case is Co2, not the actual relative humidity/heat. I'm not the one to give you any advise on running sealed rooms with Co2, but what I can say for sure is plants can do very well on very low humidity and high temps. It's not an ideal scenario, but in my own experience it has never caused me those problems.

I know people with experience of running sealed, co2-enriched rooms will be able to give you more help with your situation than I can offer. All the best

you've hit the nail on the head too papaduc,
Ive been growing since 2010 indoors and since mid 70s oustside.
indoors Ive never had any issues with humidity and Ive dealt with these Rhs before w/no issues.
its the enriched Co2 atmosphere and i know this.
I believe VPD is more of an prob in this type of enviroment,
ive never experienced it before this.

but this is just part of my *learning curve* going into a highly controlled Co2 enriched enviroment,
and i expected issues
but too low Rh in day hours blindsided me...
never saw that one coming lol

I have a humidifier incoming soon so til then i have to spray 3-4 time daily

thanks for all the help eveyone
:tiphat:

DankemsHunter · Feb 27, 2015

Heres a nice chart

r2k · Jul 7, 2015

Props to this thread, I was going to create something similar but I don't need to repeat what was said previously in this thread.

I understand what VPD is and how to calculate it, but what I don't know is the Ideal value, optimal range of VPD, and acceptable range for Cannabis. Does anybody have such values? I extracted them from the chart that DankemsHunter shows above, but I don't know if I trust them. The web site that posts that chart doesn't list them. I don't know if it some person's dream of what they think, or if it is really correct with data to back it up.

Does anybody have known good ranges for VPD on Cannabis? I will take it in any units you want (kPa, millibars, inches of Hg, etc). I would like to publish an actual line graph of VPD values (not some colored number chart with quantized values) but I don't know what ranges to use. I have the chart done, I just need trusted ranges.

-r2k

the gnome · Jul 7, 2015

Billy104 · Aug 31, 2015

according to formula for vpd at 80 degrees humidity should be at 75% not 60% like kca r says in beginning unless I am doing formula wrong

noyd666 · Aug 31, 2015

that is what mine is running on at moment 80f=75%.

the gnome · Aug 31, 2015

when i had VPD issues running sealed the 1st time I found out you don't need to run down the middle of the chart, unless you want to.
as long as your in the white secondary section of the chart you won't suffer VDP symptoms
running 60% like Kcar may not have been in the ideal range on the chart,
plants do very good

Billy104 · Aug 31, 2015

Was suffering from symptoms like kcar pics. I came to conclusion that it was my vpd being off. I raised humidity to about 73% at 79 degrees. Not to long after co2 was on the same symptoms showed up. Any input would be appreciated. New to co2 and trying to figure it out

Billy104 · Aug 31, 2015

Gnome... Looks like you had same situation I have. I was sure humidifier would fix it but it hasn't. Heads up on humidifier, run a RO filter or mineral filters or it will atomize the calcium in the water and leave a powder all over everything.

dr-dank · Aug 31, 2015

Just came across this thread. Never heard of VPD. But, I believe its just what I have...

Passive cooling via lots of air, so-cal low humidity, 600 watt over 2x3, kinda close to plants. I hit 84 last night and believe the RH was below 50%. Have added a second gauge; the one that has been baking under HID a few years said RH was at 13%!!!!!

Have switched the 600 W to run at 75% and will plumb in humidity when light on to see if it helps. Some of my plants look much like OPs...

Thanks much!

the gnome · Aug 31, 2015

while i waited for *over a week*(fuctuP ordering shit) for my humidifier to arrive it was obvious i would lose plants before then so i got a garden sprayer w/water and sprayed the plants and the concrete floor to keep RH up.
in 3-5days symptoms backed off to where things were looking good.if you think you have VPD do this and see what happens before buying a humidifier, they're not cheap for larger rooms(mine is 14 x 20)
mine was around $350 and get this
by the time my hum. came in the plants had grown enuff to transpire more and raise the RH and symptoms backed off.
in my situation if i hit 55-50% i was seeing the symptoms and below that things degraded quickly to where i was sure i would lose the crop.
here's the thing, VPD was never a factor in my nonsealed/CO2grows, i would be 35%RH and be fine.
it's when i went sealed the VPD readed it's ugly head.
so VPD can be a thing thats hard to figure out because under different circumstances but same envir. conditions you can have VPD or not

dr-dank · Sep 1, 2015

Thanks Gnome. I am small scale and so used an old ultra sonic for now. Did not make a great impact to humidity with all the air moving. But getting cooler now.

Regards

dr-dank · Sep 7, 2015

Thanks waxy!

I can't wait for it to cool down so I can switch one of the two 6" fans over to temp. Right now I have so much air coming in its hard to get the humidity high.

Also, using the salt in plastic bag deal to test my hygrometer. Should read 75% according to the web....The think seems stuck at 50% in the closet. My other/older never goes above 20. I know its fooked.

led05 · Oct 27, 2015

VPD Guidelines

VPD Guidelines

I'd follow the Tomato guidelines and follow-up on these studies if wanting more details, solid and relevant.

"Growers should aim to have fairly low VPD, for example 0.3 kPa, when rooting cuttings in greenhouses. This will reduce the drying of young plants, thereby reducing the frequency of misting and watering required to keep plants hydrated. However, Michigan State University Extension recommends maintaining a greater VPD (greater than 0.5 kPa) in greenhouses while finishing plants, especially when there is a dense plant canopy. Plants will be able to transpire, cool themselves and be less stressed while the environment is less conducive to disease.

Greenhouse vegetable growers harvesting fruits should be aware that one study, “Vapor Pressure Deficit (VPD) Effects on the Physiology and Yield of Greenhouse Tomato,” reported that a VPD of 0.8 kPa during the day and night increased photosynthetic rates and tomato fruit yields compared to plants grown with a VPD of 0.5 kPa. Too dry of an environment can also cause problems. For example, another study, “High Vapor Pressure Deficit Influences Growth, Transpiration and Quality of Tomato Fruits,” showed that a very high VPD of 2.2 kPa could cause plant stress and fruit cracking in tomato.

Vapor Pressure Deficit - VPD and Nutrient Deficiency

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