Jon's Final Florida Journal For Real

[NickHardy]

Ultimate VPD Guide

This is from the manufacturer of the device I have. It cites its references at the end but its quite a read. To get to the leaf offset I can also adjust the calculation in the app. But ai run with their standard template.

Nick

 

[Keffka]

VPD has very little to do with light whatsoever.



I mean the heat your light gives off will alter it but it has nothing to do with PPFD or DLI or anything light related.

Here’s mine now, veg: (NB - Light reading was 5 Days ago but probably much different now, like 850)

In order for a plant to photosynthesize more nutrients, VPD needs to be on point, helping to bring the nutrients into the plant in the first place. To be able to utilize those additional nutrients through photosynthesis, the plant needs more light. VPD is linked to light quite intimately. It’s all linked together intimately, and VPD is a grouping of some of those links. It can be used to find the optimal amount of light a plant can utilize for photosynthesis.

VPD is a measure of Room temp, rh, and leaf surface temp. A lot of VPD monitors assume your plant LST is 2 degree below room temp, however that’s only true when your plant is receiving optimal light.

You would need to take the actual LST to know for sure whether or not your VPD is on point, otherwise only having room temp and rh leaves you guessing at the true VPD for your plant.

 

[Gee64]

From your link you posted. Lol Nick needs to read the instructions closer. Sorry Nick, not poking fun. Room VPD and leaf VPD are 2 very different animals. People get them confused all the time. The companies who sell you things prey on it.

"How to calculate leaf VPD:

1. Figure out the air SVP (ASVP)​

   • Same formula as getting the SVP for air VPD

2. Figure out the leaf SVP (LSVP)​

   • It is the same formula as ASVP, but you use the leaf temperature in your calculation (typically 1-3 °C or 2-5 °F cooler)

3. Leaf VPD = LSVP – (ASVP x RH/100)"​

​

and also from your guide:

"

How you can influence and change VPD:​

1. Temperature​

   • Increase temperature (run a heater or reduce AC): increase VPD
   • Decrease temperature (increase AC): decrease VPD

2. Humidity​

   • Increase humidity (run a humidifier): decrease VPD
   • Decrease humidity (run a dehumidifier): increase VPD

3. Light Intensity​

   • Increase light intensity (move lights closer, etc): increase leaf temps: increase VPD
   • Decrease light intensity (move lights farther, etc): decrease leaf temps: decrease VPD.

 

[Keffka]

Room VPD and leaf VPD are 2 very different animals

Room VPD is fairly meaningless and it’s annoying that companies tout it like it’s some sort of beneficial feature. I guess once you’ve got your light dialed in it could be handy but the moment you grow anything other than that specific pheno you’ll need to get the LST again.

 

[Gee64]

Room VPD is used to calculate a dew point.

 

[Vegan4life]

If he can’t I may be able to. What app are you using? And the plants are definitely on the mend. Good work.

Good evening @Jon , I just put the photone app on my iphone X and bought the full spectrum led add on. I am using quantum boards, 3 different fixtures in my tent, 1 - rspec, 1 - 2700K and 1 - 3500k. Each fixture is 260 watt. Do I need to calibrate the app or will it work ok without calibration? Also would I need to re-calibrate for each fixture? I just adjusted lights to 1000 ppfd at top of canopy, directly below center of each fixture (using app with diffuser).

 

[Jon]

Good evening @Jon , I just put the photone app on my iphone X and bought the full spectrum led add on. I am using quantum boards, 3 different fixtures in my tent, 1 - rspec, 1 - 2700K and 1 - 3500k. Each fixture is 260 watt. Do I need to calibrate the app or will it work ok without calibration? Also would I need to re-calibrate for each fixture? I just adjusted lights to 1000 ppfd at top of canopy, directly below center of each fixture (using app with diffuser).

Hey @Vegan4life - nope, sounds like you’ve done it all exactly right. You can tell if you need to calibrate by comparing the app to the par chart of the light. You should be fairly close. If so, you’re in business. If you’re 100s off, calibrate.

 

[Jon]

Room VPD is used to calculate a dew point.

Loving all the VPD talk as it’s something I need to learn. That said, for the new or average grower, VPD is about the last thing they need to worry about. Obviously in organics it’s essential. And probably behooves everyone to know and try to adhere to regardless of style. But again - new and lesser experienced growers ain’t gonna hit VPD on purpose. There’s way too many factors involved. I’m not exactly new and it’s not the easiest thing in the world for me. You know?

 

[Vegan4life]

Loving all the VPD talk as it’s something I need to learn. That said, for the new or average grower, VPD is about the last thing they need to worry about. Obviously in organics it’s essential. And probably behooves everyone to know and try to adhere to regardless of style. But again - new and lesser experienced growers ain’t gonna hit VPD on purpose. There’s way too many factors involved. I’m not exactly new and it’s not the easiest thing in the world for me. You know?

Especially hard when your humidity rises to 70% and above...

 

[NickHardy]

From your link you posted. Lol Nick needs to read the instructions closer. Sorry Nick, not poking fun. Room VPD and leaf VPD are 2 very different animals. People get them confused all the time. The companies who sell you things prey on it.

"How to calculate leaf VPD:

1. Figure out the air SVP (ASVP)​

   • Same formula as getting the SVP for air VPD

2. Figure out the leaf SVP (LSVP)​

   • It is the same formula as ASVP, but you use the leaf temperature in your calculation (typically 1-3 °C or 2-5 °F cooler)

3. Leaf VPD = LSVP – (ASVP x RH/100)"​

​

and also from your guide:

"

How you can influence and change VPD:​

1. Temperature​

   • Increase temperature (run a heater or reduce AC): increase VPD
   • Decrease temperature (increase AC): decrease VPD

2. Humidity​

   • Increase humidity (run a humidifier): decrease VPD
   • Decrease humidity (run a dehumidifier): increase VPD

3. Light Intensity​

   • Increase light intensity (move lights closer, etc): increase leaf temps: increase VPD
   • Decrease light intensity (move lights farther, etc): decrease leaf temps: decrease VPD.

In 20 pages its the only mention light gets.

 

[NickHardy]

Especially hard when your humidity rises to 70% and above...

Not really, helps keep it up. My background Rh is say 75% 24/7/365 - at night not uncommon to get 90% in the tents/rooms.

I can choose my leaf offset. I have it on 0 - sensor is right there. In the leaves. Maybe I’ll take a baby thermometer but if its more then 1c difference I doubt it.

 

[Keffka]

Not really, helps keep it up. My background Rh is say 75% 24/7/365 - at night not uncommon to get 90% in the tents/rooms.

I can choose my leaf offset. I have it on 0 - sensor is right there. In the leaves. Maybe I’ll take a baby thermometer but if its more then 1c difference I doubt it.

Here, do this, it’s also from the link you shared

 

[Jon]

Blackberry Moonrocks

Two questions: will it be even close to the 33% potential as advertised? And, will what I have turn into what they show the buds to look like?

Btw - so I downloaded this picture from the Blimburn site to my photos, then tried to post. The system wouldn’t allow it. Then I cropped out the Blimburn logo. Voila. Good to know.

 

[Absorber]

Btw - so I downloaded this picture from the Blimburn site to my photos, then tried to post. The system wouldn’t allow it. Then I cropped out the Blimb

They must have changed something recently then because I did exactly that to add photos of the Canuk strains I was doing to my journal those pictures had Canuk logo on them

 

[NickHardy]

Here, do this, it’s also from the link you shared

If you’d have read my post you’d have seen the picture of just where to do it in the App I use for that very purpose. i own one. I’d probably be going up not down.

 

[Melville Hobbes]

They must have changed something recently then because I did exactly that to add photos of the Canuk strains I was doing to my journal those pictures had Canuk logo on them

Canuk are sponsors, Blimburn aren't.

 

[Gee64]

Not really, helps keep it up. My background Rh is say 75% 24/7/365 - at night not uncommon to get 90% in the tents/rooms.

I can choose my leaf offset. I have it on 0 - sensor is right there. In the leaves. Maybe I’ll take a baby thermometer but if its more then 1c difference I doubt it.

So under optimal conditions a leaf wants to be 2 degrees F lower than air temp. You are supposed to take a leaf temp reading and program the actual offset into this meter. If it's less than 2 degrees then the light is too close or turned up too bright.

VPD is even more vital if you use CO2. The wrong VPD can inhibit CO2 absorption.

You should research this a bit. As the manual says, correct VPD can bring a bigger yield than CO2.

What they mean is a non CO2 grow with proper VPD can give you a better yield than using CO2 at the wrong VPD levels.

VPD controls stomata, and stomata are the throttle for a plant. A plant is just a pump, and stomata regulate the speed that the pump can run at, so if it's wrong, more food or light or CO2 won't make them grow faster or bigger.

If the pump runs too fast it pulls in raw water without any nutes, and deficiencies start. If its running too slow you die of old age without growing as much as you could have.

You should be taking a leaf temp reading every day about 2 hours before lights out, and adjusting that offset accordingly, which will regulate your CO2 properly.

As light increases, your leaves work harder and warm up, just like people do when they exercise. So light is the driver behind leaf temp, not air temperatures.

A two degree difference is the perfect temp difference for maximum transpiration without causing harm.

The warmer air sucks water out of the plant. A two degree difference creates the perfect amount of suction, and the atmosphere drinks water from the ground through the plant like a straw, pulling nutes from the soil in with it.

The stomata are the restrictors in the straw. When VPD is correct, the stomata open up completely. Now CO2 can be absorbed properly.

VPD is physics, not biology, so it's a constant. It sets the stage for the grow. You set the VPD and the plant acts accordingly. Everything else is effected by VPD just as soil is effected by calcium.

If your air temp is 76, leaf temp 74, and RH is 48%, your VPD is 1.40.

If humidity plunges to 41%, you lower the room temp to 72, adjust the light to get a leaf temp of 70, and VPD is again 1.40.

The plant runs at the same speed under 2 very different climates just by monitoring VPD and adjusting.

It never missed a beat.

OK everyone, regardless of how you grow, if you don't understand VPD you should research it. If you are unfamiliar with it, then you are in for a really great treat. It's a game changer. Alot of problems disappear.

Overwatering is hard when a plant is moving water correctly, so that also fixes oxygen intake.

It steadies a grow.

My grow is a good example, it's a disaster. The light failed, then the replacement got turned up too high for a week, then I had to drench the pots because the 1st run soil mix was acting up, and I fried all the leaf tips to fix the soil but.... The buds are fantastic. Big, resineous, and stinky.

VPD is the only reason my crop survived. For everything that went wrong, a good environment carried them through so far, and if I stay on it I will have a splendid harvest.

If you are learning how to grow, its a basic skill you need, if you are an advanced grower, you are about to go up a full level.

 

[Gee64]

If you are brand new to growing, VPD is one of the most valuable skills to learn.

It's how a plant moves water. Water brings food. Food makes plants grow.

It regulates CO2 intake. Plants eat CO2.

Wrong VPD means your stomata aren't set properly so the pump isn't supplying optimal food.

 

[NickHardy]

I shall certainly try and make some time to learn about it, thanks @Gee64

Nick

 

[Gee64]

Blackberry Moonrocks

Two questions: will it be even close to the 33% potential as advertised? And, will what I have turn into what they show the buds to look like?

Btw - so I downloaded this picture from the Blimburn site to my photos, then tried to post. The system wouldn’t allow it. Then I cropped out the Blimburn logo. Voila. Good to know.

I think that if you properly adjust your night time temps moving into senescence that your weed will be prettier. As for thc%, well who knows if they are telling the truth, but it looks strong.

Thats a beauty plant Jon. Too bad you can't clone it. It would be a great pheno to figure out perfectly and grow a whole bunch of.