Vapor Pressure Deficit or VPD. Which chart is right and why so much variance?

[IamN2pot]

For another first for the old dirt farmer, VPD. I'm gonna need some help getting a final setup for this, please!
I've purchased the AC Infinity line of exaust fan, 69 controller, smart outlet (for heater) and their small humidifier. Oh, and I'm in Pueblo Co where the RH has been in the single digits the past week with gust up to 60mph and my garage is my lung room. Nope, I don't need a de-humidifier. So I have the fan set up just the way I want it, constant on #1 and incrimental increases from 74* - 80* to raise the fan up to #7. I also have set it to raise the fan speed to #2 if the humidity reached 65%. Works great, I suposed, until I started reading multipal VPD charts. Yes, I know, the target VPD changes with life stages. That's not what I'm talking about. I see one chart telling me that @ 70*/35%RH = 1.62VPD. Next chart, same 70* or 20*C at 34% and 36%RH = 1.02 and 1.01VDP?
WHAT!!!!!!!
So last night I set my heater to keep 70* and the humidity dropped to 35-36% RH. (screenshot) I'll take it that since the AC Infinity app has my VPD overnight running from 1.56-1.61, I should use the first chart?
During 'MY' day, it's easy to just set the AC humidifier to 60% RH and the humidifier does fine with the VPD, running in the 1.10 range, and running on it's own (not connected to the 69 controller). I want to learn if/how to set it up to run with all 3, cooling (vent), heat and humidifier, working together. THis is in my soil tent, for now, and has come to the forfront because IMO, the 'stiff drooping' of the leaves is from humidity being in the mid 20 to low 30% range the past couple weeks.
That said, I have been wrong before, just ask my wide. Hahaha!!!

First 2 pics are from yseterday of the 3 plants. 3rd picture is of them today. The worst one from yesterday is the one closest in todays picture of all 3. A marked improovement, if I do say so. Makes me think I'm on the right cure for that problem???

https://scynceled.com/wp-content/uploads/2019/11/Scynce_VPD_chart-01.png

verses from 420Magazine no less,

https://www.420magazine.com/community/attachments/vpd-chart-gif.2209232/

EDIT: LOL, forgot to add the screenshot of an hour with the lights and humidifier off last night. Fan and heater were 'on'. VPD ran 1.59-1.61VPD. THat top line in the screenshot is of the current conditions, VPD 1.01.

 

[SweetLeafGrow]

The new photo def looks better.

How are you calculating your VPD? Are you taking leaf temperature?

This is the chart I use. Did not realize there are variances between the different charts. Not sure how accurate this is.

VPD Chart

Vapor pressure deficit (VPD) chart & calculator for horticulture in controlled environment. Cannabis, tomatoes, leafy greens, cucumber.

vpdchart.com

 

[IamN2pot]

I just have the temp/RH probe for the 69 controller hanging at canopy height from the edge of the light fixture. THe other probe is from the humidifier, it's being controlled independantly. Here is a short video of what's hanging where.
View attachment VID_20230405_124510.mp4

 

[Oldsog]

Fwiw I've never cared about vpd in a room under 10x10. Imo it's worthless to worry about in a small area. Even in big rooms it's been the last on the list. Just my 2 cents

 

[SweetLeafGrow]

VPD is a 3 part calculation the way I understand it. Temperature - Relative Humidity - Leaf Temperature.

One of those hand held IR thermometer is what I use.

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www.ebay.com

 

[IamN2pot]

The new photo def looks better.

How are you calculating your VPD? Are you taking leaf temperature?

This is the chart I use. Did not realize there are variances between the different charts. Not sure how accurate this is.

VPD Chart

Vapor pressure deficit (VPD) chart & calculator for horticulture in controlled environment. Cannabis, tomatoes, leafy greens, cucumber.

vpdchart.com

...and love that chart...
Aren't leaf and air temps the same, when the probe is at or very near to the leaf or cannopy? I would also think that especially with a quantum board, like mine, there will be a huge temp variations from the edge of the tent to the center of the lamp. Maybe a 10* differance???

 

[SweetLeafGrow]

Fwiw I've never cared about vpd in a room under 10x10. Imo it's worthless to worry about in a small area. Even in big rooms it's been the last on the list. Just my 2 cents

I toss this most times too as it's hard to get the RH high enough especially when I have plants in flower in the same space. Once I get controllers in every tent I might be able to work around it. Good to hear your expertise on this @Oldsog, I have wondered how important this is in my imperfect world here.

 

[SweetLeafGrow]

...and love that chart...
Aren't leaf and air temps the same, when the probe is at or very near to the leaf or cannopy? I would also think that especially with a quantum board, like mine, there will be a huge temp variations from the edge of the tent to the center of the lamp. Maybe a 10* differance???

They could be the same but most likely they will not. I'm not experienced enough with VPD to really add more to this but I do take a look at where I am occasionally and if I can get closer to the sweet zone, I try to do that. But I do not stress about it.

 

[IamN2pot]

Fwiw I've never cared about vpd in a room under 10x10. Imo it's worthless to worry about in a small area. Even in big rooms it's been the last on the list. Just my 2 cents

Same here. I never knew what a VDP was untill a few months ago. That said, I do think adding the humidity has helped with the stiff drooping.

 

[Cool_Beans]

Not sure if you already did this but leaf temp differential can he set in the Controller 69. The displayed vpd wasnt jiving with what I was seeing until I sorted that out.

I kept mine between .80-1.0 vpd while in veg. Around 78-80F @ ~65% rh for a ballpark.

 

[SweetLeafGrow]

I did not know that. I would think you still need to know what that difference is so that you could input the correct differential, unless I am missing something here.

I would assume that "leaf temp differential" is the difference between the ambient temperature and the leaf temperature. Unless I am just way off base here, you would still need to know that to set your controller properly.

 

[IamN2pot]

Not sure if you already did this but leaf temp differential can he set in the Controller 69. The displayed vpd wasnt jiving with what I was seeing until I sorted that out.

I kept mine between .80-1.0 vpd while in veg. Around 78-80F @ ~65% rh for a ballpark.

No, I wasn't aware of any 'leaf temp diff..." setting in the 69. Keep going......
Your temps and RH are close to my reading, during the day. What are your night, lights out, temp and RH readings?

 

[SweetLeafGrow]

Not sure if you already did this but leaf temp differential can he set in the Controller 69.

I was going by what @Cool_Beans said here. I'm not familiar with these controllers yet but just guessing here trying to help. I think CB might have nailed it.

 

[IamN2pot]

Oh crap, got stoned and I missed it! That was @Cool_Beans that said that! Anywho....you get what I'm saying?

LOL, I'm in need of instructions for the 69 controller as well. So we're in the same boat. Just waiting for someone who knows how to drive it....
and looks like Cool_Beans knows alot more about it than either of us...

 

[SweetLeafGrow]

So I am wondering here, does this fan kit have the same 69 controller that you guys are using? The photos do look the same but wanted to get the best I can when I get this order put together.

CLOUDLINE PRO T6, Inline Booster Duct Fan 6â Cooling Vent Exhaust Grow Tents | eBay

CLOUDLINE SERIES - T6. Go even further by setting a minimum speed that the fan will run at constantly and would only increase when triggered. It can also connect to your favorite grow light and outlet device from outside the UIS platform using select adapters.

www.ebay.com

 

[Cool_Beans]

No, I wasn't aware of any 'leaf temp diff..." setting in the 69. Keep going......
Your temps and RH are close to my reading, during the day. What are your night, lights out, temp and RH readings?

It stays the same. Heat comes on if it drops below 78f w a 2 degree buffer, humidifier if it goes below 60% w 2% buffer, and I run the exhaust on a cycle-1min every 30min on low just to exchange the air. If plant gets big enough to where I need to keep humidity down vs up, I'll switch to having the exhaust regulate that.

 

[Cool_Beans]

So I am wondering here, does this fan kit have the same 69 controller that you guys are using? The photos do look the same but wanted to get the best I can when I get this order put together.

CLOUDLINE PRO T6, Inline Booster Duct Fan 6â Cooling Vent Exhaust Grow Tents | eBay

CLOUDLINE SERIES - T6. Go even further by setting a minimum speed that the fan will run at constantly and would only increase when triggered. It can also connect to your favorite grow light and outlet device from outside the UIS platform using select adapters.

www.ebay.com

Imo the 69wifi is the bees knees, so you order the fan you want with just the basic dial control, and the standalone controller 69 wifi. The basic controller 69 has bluetooth which is really only useful for programming changes since you need to be within range, which isnt far.

 

[Cool_Beans]

I did not know that. I would think you still need to know what that difference is so that you could input the correct differential, unless I am missing something here.

I would assume that "leaf temp differential" is the difference between the ambient temperature and the leaf temperature. Unless I am just way off base here, you would still need to know that to set your controller properly.

What I did was take my IR temp gun and measure leaf temps at various places across the canopy then guesstimate an avg leaf temp. Say the temp reading on the controller 69 reads 78F in the tent, and the leaf temp avg I measured was 74F, I input -4 for the leaf temp offset differential.

 

[IamN2pot]

So I am wondering here, does this fan kit have the same 69 controller that you guys are using? The photos do look the same but wanted to get the best I can when I get this order put together.

CLOUDLINE PRO T6, Inline Booster Duct Fan 6â Cooling Vent Exhaust Grow Tents | eBay

CLOUDLINE SERIES - T6. Go even further by setting a minimum speed that the fan will run at constantly and would only increase when triggered. It can also connect to your favorite grow light and outlet device from outside the UIS platform using select adapters.

www.ebay.com

Here @SweetLeafGrow , https://acinfinity.com/smart-controllers/

All of the 69 controllers, as best I know, only diff is how it connects to the app. The Pro that came in my combo kit has both BT and WiFi option. The other 2 69 models have either BT or WiFi. All the other fetures are the same.

 

[steamroller]

I use these VPD charts.
The numbers change depending on the difference of leaf temp compared to room temp.

Vapor Pressure Deficit VPD Calculator - Dimlux Lighting - The Best Grow Lights

Vapor Pressure DeficitCalculator Calculate both Room VPD and Leaf VPD automatically Just enter the value below to generate the VPD values for your room and your plants. You’ll need to know the room’s temperature, relative humidity, and the plant’s temperature. We recommend calibrating your...

www.dimluxlighting.com

 

[Anthem275]

For another first for the old dirt farmer, VPD. I'm gonna need some help getting a final setup for this, please!
I've purchased the AC Infinity line of exaust fan, 69 controller, smart outlet (for heater) and their small humidifier. Oh, and I'm in Pueblo Co where the RH has been in the single digits the past week with gust up to 60mph and my garage is my lung room. Nope, I don't need a de-humidifier. So I have the fan set up just the way I want it, constant on #1 and incrimental increases from 74* - 80* to raise the fan up to #7. I also have set it to raise the fan speed to #2 if the humidity reached 65%. Works great, I suposed, until I started reading multipal VPD charts. Yes, I know, the target VPD changes with life stages. That's not what I'm talking about. I see one chart telling me that @ 70*/35%RH = 1.62VPD. Next chart, same 70* or 20*C at 34% and 36%RH = 1.02 and 1.01VDP?
WHAT!!!!!!!
So last night I set my heater to keep 70* and the humidity dropped to 35-36% RH. (screenshot) I'll take it that since the AC Infinity app has my VPD overnight running from 1.56-1.61, I should use the first chart?
During 'MY' day, it's easy to just set the AC humidifier to 60% RH and the humidifier does fine with the VPD, running in the 1.10 range, and running on it's own (not connected to the 69 controller). I want to learn if/how to set it up to run with all 3, cooling (vent), heat and humidifier, working together. THis is in my soil tent, for now, and has come to the forfront because IMO, the 'stiff drooping' of the leaves is from humidity being in the mid 20 to low 30% range the past couple weeks.
That said, I have been wrong before, just ask my wide. Hahaha!!!

First 2 pics are from yseterday of the 3 plants. 3rd picture is of them today. The worst one from yesterday is the one closest in todays picture of all 3. A marked improovement, if I do say so. Makes me think I'm on the right cure for that problem???

verses from 420Magazine no less,

View attachment 162 View attachment 163 View attachment 164


EDIT: LOL, forgot to add the screenshot of an hour with the lights and humidifier off last night. Fan and heater were 'on'. VPD ran 1.59-1.61VPD. THat top line in the screenshot is of the current conditions, VPD 1.01.
View attachment 165

Depending on where you live the first chart can get you into trouble.

 

[moe.red]

I think in general VPD is misunderstood. Especially by the old time growers.

You can't "not use VPD." It is nothing more than a metric which describes a portion of your environment.

The question is not should I use VPD (you are whether you like it or not) the question should be what does my VPD need to be for this stage in my grow?

If you understand this, the chart becomes irrelevant. I'll elaborate when I have more time. Perhaps a sticky thread coming.

Here's the short version -

VPD is a measure of how fast your plants are breathing. Plants breathe by opening and closing stomata. Where you set your environment will in part determine how much carbon in the form of CO2 is taken into the plant, and subsequently turned into sugar, the whole point of photosynthesis

It is but another tool for tuning your grow. You can ignore it and still grow good weed. Especially in soil.

I find that when you are growing in a fast method like RDWC or Fog, and you do not have it right, symptoms occur. Especially when running CO2 and high PPFD to grow fast.

If everything you do is kinda low and slow, environment is not as important, you are growing in a style that is more forgiving. If you are pushing plants, even if you are not actively measuring VPD, you have it correct or you have symptoms like taco leaves for example.

If you choose to lower RH because of mold, but do not change temp to match, you are slowing down your grow, simple as that. That's cool, do that. Don't get mold. But all this stuff is like a balloon. You squeeze on one end, it bulges out in another.

 

[moe.red]

I want to learn if/how to set it up to run with all 3, cooling (vent), heat and humidifier, working together.

OK, so first is your target of about 1 is a great starting point for VPD. If you can get there you can rule that out as the cause.

Forget the charts for today, just focus on the number. It means the stomata are open, and there is room in the air for plant respiration to release water. So plant = turned on as far as environment goes (assuming there is water available to move thru the plant.)

Plant = turned off can cause all sorts of problems like lack of turgidity displayed in your pics. Respiration is the number 1 variable in leaf turgor pressure. It's why when plants go to sleep they droop. Because respiration shuts down without light. Natural stuff, makes sense. Nighttime processes are about hormones not photosynthesis - no respiration required for that stuff.

What you are doing is the way to control all 3. If you want to automate the process, just plug the humidifier into the same timer outlet as the lights.

As soon as you get this right the plants should respond. Like in front of your eyes. I don't see a lack of turgidity in the new photo. Colors via photos can be deceiving, everything else good?

 

[IamN2pot]

... everything else good?

LOL, all in ones perspective I suppose. Went out to the garage this morning and there was a damp spot in the middle of our walk path into the house, outside the dirt tent. What??? Further investigation showed me that running the 'hose' included with the Cloudforge T3 at a downward angle is a no no. I sat the humidifier outside the tent, for ease of filling and keeping an eye on. I ran the hose from the top of the T3 down through the 8" vent opening on the Spider Farmer tent and let it lay on the floor of the tent, about 8-10" behind a circulation fan to distribute moist air. WRONG!. Overnight it made a small stream that trickled through the SF tent tray and out the tent onto the garage floor and on out the garage. Darnest thing, RDWC has 15+ gallons of circulating water, water pumps and lines and has stayed dry. Dirt tent had no water inside it, just fog from the T3 humidifier and it flooded. WHAT!!! ...and I'm off fo another days adventures in gardening.
I also confirmed 3 more males, 2 in the RDWC and 1 in the dirt. This has also been my worst ratio of M to F ever. The current count is 9 M, 1 F and 3 undetermined (including tripod). And speaking of tripod, I've discovered that 3peat trait in my 1 female in dirt. I've taken 5 cuts from her laterals and 2 of them are tripods. I'll post pics etc over in my Wacky plant thread.
Thanks for the solid number for VDP. Funny thing is, I was thinking something around a 1.0 VPD would be about right for them at this stage of growth.
Here is what the climate has looked like over the past hour. The spike at 7:45 is when I had it open to show the wife how I flooded a tent without any water in it, Hahaha!

 

[smoke]

For another first for the old dirt farmer, VPD. I'm gonna need some help getting a final setup for this, please!
I've purchased the AC Infinity line of exaust fan, 69 controller, smart outlet (for heater) and their small humidifier. Oh, and I'm in Pueblo Co where the RH has been in the single digits the past week with gust up to 60mph and my garage is my lung room. Nope, I don't need a de-humidifier. So I have the fan set up just the way I want it, constant on #1 and incrimental increases from 74* - 80* to raise the fan up to #7. I also have set it to raise the fan speed to #2 if the humidity reached 65%. Works great, I suposed, until I started reading multipal VPD charts. Yes, I know, the target VPD changes with life stages. That's not what I'm talking about. I see one chart telling me that @ 70*/35%RH = 1.62VPD. Next chart, same 70* or 20*C at 34% and 36%RH = 1.02 and 1.01VDP?
WHAT!!!!!!!
So last night I set my heater to keep 70* and the humidity dropped to 35-36% RH. (screenshot) I'll take it that since the AC Infinity app has my VPD overnight running from 1.56-1.61, I should use the first chart?
During 'MY' day, it's easy to just set the AC humidifier to 60% RH and the humidifier does fine with the VPD, running in the 1.10 range, and running on it's own (not connected to the 69 controller). I want to learn if/how to set it up to run with all 3, cooling (vent), heat and humidifier, working together. THis is in my soil tent, for now, and has come to the forfront because IMO, the 'stiff drooping' of the leaves is from humidity being in the mid 20 to low 30% range the past couple weeks.
That said, I have been wrong before, just ask my wide. Hahaha!!!

First 2 pics are from yseterday of the 3 plants. 3rd picture is of them today. The worst one from yesterday is the one closest in todays picture of all 3. A marked improovement, if I do say so. Makes me think I'm on the right cure for that problem???

verses from 420Magazine no less,

View attachment 162 View attachment 163 View attachment 164


EDIT: LOL, forgot to add the screenshot of an hour with the lights and humidifier off last night. Fan and heater were 'on'. VPD ran 1.59-1.61VPD. THat top line in the screenshot is of the current conditions, VPD 1.01.
View attachment 165

If you can get your temp up closer to 80 deg your plants will thank you for it.

I run hps and my leaf temperature is about 3 to 4 degrees less than room temperature. I dont run co2, with co2 increase your room temp to 82/83

 

[IamN2pot]

Yep, those temps are the result of a garage lung room and the outside temp today, 18* - 57*. Tomorrow will be 10* warmer and by Sunday, 40* - 78*. I'll be itchin to get out side and into my garden patches. Garage temp is 63* right now. so with that SF4000 set on 300 watts, she can heat up about 10-12 degrees and as summer comes on, it will hold within 4* with the fan on 7 or 8 and the garage about 80* and at full 450w power. It's a fun balancing act from winter to summer in the garage. LOL, just saw the weather, 88* for Wed high. Whew...... perfect for me!!!

 

[moe.red]

That sounds a lot like me when I was getting all the crap set up. I had more spills and floods than I care to admit. Good thing for shop vacs.

I think you are just in a position that your lung room is far enough away from where you want the conditions to be that you will never achieve all things you want together. Raising the temp to high 70s is going to make the RH dive.

Short of addressing the lung room, you are just gonna have to do the best you can.

That M/F range seems really unlucky. Personally I run a lot of feminized stuff so I don't have to deal with that. Hydro is less forgiving than soil, can't just add a bucket or reposition things to accommodate starting with double the plants you intend to finish with, so I run fems or do the M/F sorting before going into the RDWC. Pretty much nothing but confirmed females go in there. Too much of a PITA dealing with males at that point.

 

[IamN2pot]

Couldn't agree more. Not the wisest move from me to start reg seeds in that RDWC. I will say that I made 4, 3 site lids, for up to 12 seedlings, but next round will be from clones. As for the garage lung room, yep, I agree. It's far from perfect, but it's what I've got and at least in dirt, does way more than I need from it, so it's ALL good! I'll try to keep it as close to 1.0 as I can. I'm alot closer now than the 2.0-2.5 without any additional fog.
The M to F thing tickles me. Now I know how some parents feel after half a dozen or more trys that are all boys or girls. Do you remember the Jewish patriarch Jacob (Israel)? Anyway, he had 12 boys and only 1 girl, so I'm still good.

 

[GrumpAzz]

If you can get your temp up closer to 80 deg your plants will thank you for it.

I run hps and my leaf temperature is about 3 to 4 degrees less than room temperature. I dont run co2, with co2 increase your room temp to 82/83

With your temps around 80, do you run a chiller? I've kept mine 74-77 and my water temps have remained 72-74.

You may be in dirt, sorry if I missed that somewhere.

 

[Rootsruler]

I use the first chart you posted as a guideline as to where I want both setpoints to run into each other. Depending on the stage I'm at and the temperature I've been dealt it guides me in where I want humidity to be at that temperature. I double check VPD numbers with a laser temp monitor and, so far, the results have been vibrant, strong plants. I haven't even had a hint of any mold or pests in the tent and I chalk that up to the health of the plant. Regardless of my cleanliness protocols I probably have mites or mildew in the tent but the plant health isn't letting it get a foot hold.

This run I decided to run veg at a higher humidity level than I did the last run and I can see a difference in regards to the health of the girls. Growth seemed to really be accelerated when they're in the sweet spot for a prolonged period of time. I've also noticed that the higher humidity levels seemed to have increased the terpene profiles as it's getting stinky in the tent. Probably more about the genetics but I definitely notice a difference.

One of the master growers I worked with was from Holland. IIRC, his name was Girt. Don't remember his last name. He told me he had worked under another master grower from Holland named something De Jong. Don't remember the first name. No idea who his mentor is but he taught me a lot about growing weed. He told me his goal was to be able to provide an environment similar to a field out in the middle of nowhere with nothing stressing the plants out and as consistent an environment for the phase of growth the plants were in. He was the one that taught me that less is more when it comes to growing. As close to nature as possible, tweeking here and there to push at the appropriate time.