VPD (vapor pressure deficit)

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FourthCity

FourthCity

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Much obliged FourthCity, I will be referencing your spreadsheet.
Just for the sake of clarity could you comment on the vpd calc from pulsegrow that I posted.
You want to work with the plant's vpd, not the air vpd. The calculator you are looking at just refers to plant vpd as leaf vpd, you can disregard air vpd as the plant's vpd tells you everything you need to know. From the page you linked to, right above the calculator:
https://pulsegrow.com/blogs/learn/vpd#calc said:
However, since the inside of a plant is water, the plants feel a different VPD than just the normal Air VPD. If you want to figure out what’s going on with the plant, you need to consider the cooling effect of evaporating water as it exits the leaves’ stomata. To calculate this, you need to know the difference between the air temperature at canopy level, and the temperature of the leaves. An IR thermometer is useful for this.
 
SupaC

SupaC

26
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You want to work with the plant's vpd, not the air vpd. The calculator you are looking at just refers to plant vpd as leaf vpd, you can disregard air vpd as the plant's vpd tells you everything you need to know. From the page you linked to, right above the calculator:

Thanks so much FC .
I have been running the air vpd for months in a sealed room, and have nothing but problems.
Will dial in for Leaf Vpd .

May I ask what temps and RH you recommend if running co2 ?
By temps I mean canopy ( in the shade midway down the plants? ) just to be clear.

I am aware that most people running co2 prefer the low 80's , but again no clarity on where they are measuring these temps..
 
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FourthCity

FourthCity

778
143
Thanks so much FC .
I have been running the air vpd for months in a sealed room, and have nothing but problems.
Will dial in for Leaf Vpd .

May I ask what temps and RH you recommend if running co2 ?
By temps I mean canopy ( in the shade midway down the plants? ) just to be clear.

I am aware that most people running co2 prefer the low 80's , but again no clarity on where they are measuring these temps..
Your room should have one temperature and your plants should have other temperatures, small ranges in both are acceptable, large ranges suggest a problem or problems with your setup. If the top of your canopies are significantly warmer than the bottoms than you need to dim or raise your lights. The plant temps should be relatively close to the ambient room temp, generally its ok to have them get a little warmer than ambient if the room is relatively cool (room mid to low 70's) and its best to keep them a little cooler if the room is hot (room high 70's to low 80's). Both the ambient temp and rh should be consistant wherever you measure them within your room, if you are seeing a large variance look to improve your air circulation. The leaf temps are the indicators you need to follow, they will tell you how much light the plants want and what ambient temps they are happiest at, co2 or not.

Vpd hypotheticals are kinda pointless, unless you can tell me in advance what your rh and leaf temps are going to be throughout the grow I can't advise on where your ambient temps should be. Earlier in this thread there is a chart where I highlighted a green area to show the ideal operational range for your grow, target these figures as a baseline, take measurements regularly, and adjust conditions as needed to keep each plant at its target vpd.
 
ru knuts

ru knuts

254
63
I'm more confused now. I have a remote thermostat/humidistat. It's hanging on the wall at canopy level, but ~4' from the middle of the canopy. I have 2 oscilating fans just above the canopy, one blowing under the canopy, a stationary fan blowing into the corner and a ceiling fan. I have an infrared thermostat I check the leaf temp, it's generally 1-2 degrees cooler than room temp. Room temp hovers 79-81. No added CO2.
I'm in early week 4 of flowering. My VPD, the way it's set up now ranges between 1.14 and 1.34 most of the day with lights on.
I want to think I'm doing this wrong. Any suggestions?
 
SupaC

SupaC

26
13
I'm more confused now. I have a remote thermostat/humidistat. It's hanging on the wall at canopy level, but ~4' from the middle of the canopy. I have 2 oscilating fans just above the canopy, one blowing under the canopy, a stationary fan blowing into the corner and a ceiling fan. I have an infrared thermostat I check the leaf temp, it's generally 1-2 degrees cooler than room temp. Room temp hovers 79-81. No added CO2.
I'm in early week 4 of flowering. My VPD, the way it's set up now ranges between 1.14 and 1.34 most of the day with lights on.
I want to think I'm doing this wrong. Any suggestions?
Nothing wrong with your set up or your vpd.
However you are running temps best suited to co2 enrichment.
You should be fine though, but if possible try to lower your temps a few degrees and dial your vpd in again.
 
ru knuts

ru knuts

254
63
Nothing wrong with your set up or your vpd.
However you are running temps best suited to co2 enrichment.
You should be fine though, but if possible try to lower your temps a few degrees and dial your vpd in again.
I thought CO2 enrichment was best suited for higher temps ~85+?
 
SupaC

SupaC

26
13
I thought CO2 enrichment was best suited for higher temps ~85+?
This is one of those highly debated subjects.
I've read anywhere from 77 -90 even.
The general consensus seems to be the low 80's.
The temps you are running i run in my sealed co2 room.
Been growing for 10 years now, but only added a sealed co2 room 6 months ago.
So I am also on a learning curve here.
 
ru knuts

ru knuts

254
63
This is one of those highly debated subjects.
I've read anywhere from 77 -90 even.
The general consensus seems to be the low 80's.
The temps you are running i run in my sealed co2 room.
Been growing for 10 years now, but only added a sealed co2 room 6 months ago.
So I am also on a learning curve here.
Have you had a harvest since adding CO2? And the results? I have thought of adding CO2, but not sure my grow room is set up for it. My canopy is roughly 3.5' above the floor, and not in a tent.
 
SupaC

SupaC

26
13
Have you had a harvest since adding CO2? And the results? I have thought of adding CO2, but not sure my grow room is set up for it. My canopy is roughly 3.5' above the floor, and not in a tent.
I have harvested 3 times already.
Now that I actually think about it I have had that room longer.
Frankly I am not impressed with my results from the co2 room.
I pull on average a gram a watt from from my non co2 rooms, and my sealed room is delivering similar results.
That's why I'm participating in this thread, trying to learn more on how to maximize my sealed room.
Fwiw, I run all my flower rooms with vertical hps, and I grow trees, that I veg for at least 3 months.
 
ru knuts

ru knuts

254
63
I have harvested 3 times already.
Now that I actually think about it I have had that room longer.
Frankly I am not impressed with my results from the co2 room.
I pull on average a gram a watt from from my non co2 rooms, and my sealed room is delivering similar results.
That's why I'm participating in this thread, trying to learn more on how to maximize my sealed room.
Fwiw, I run all my flower rooms with vertical hps, and I grow trees, that I veg for at least 3 months.
We have different grow methods, but we're both looking for the same end results. I'm close to 13 weeks since germination and I'm in the 4th week of flowering. I have Blurples, LEDs and T5's. Pushing roughly 1372 watts from the wall. The pics were
IMG 20200324 131705800 HDR
yesterday.
IMG 20200324 131644582 HDR
 
SupaC

SupaC

26
13
We have different grow methods, but we're both looking for the same end results. I'm close to 13 weeks since germination and I'm in the 4th week of flowering. I have Blurples, LEDs and T5's. Pushing roughly 1372 watts from the wall. The pics were View attachment 954025 yesterday. View attachment 954024
Looks great.
If it was me I would have defoliated those plants a week ago.
Defoliation.
Here's another subject nobody can agree on.
 
ru knuts

ru knuts

254
63
Looks great.
If it was me I would have defoliated those plants a week ago.
Defoliation.
Here's another subject nobody can agree on.
I defoliated on the 19th and take maybe a couple dozens leaves a day off that I can't tuck under the bud sites. You should have seen it before defoliating, talk about a jungle! lol.
 
SupaC

SupaC

26
13
I defoliated on the 19th and take maybe a couple dozens leaves a day off that I can't tuck under the bud sites. You should have seen it before defoliating, talk about a jungle! lol.
Okay that's cool.
I have the same issue with the jungle like overgrowth.
Honestly don't know how anyone cannot defoliate, when dealing with so many fan leaves.
Personally I think you should give co2 a go, as you have a really dialed environment there, and your plants are very happy.
 
ru knuts

ru knuts

254
63
Okay that's cool.
I have the same issue with the jungle like overgrowth.
Honestly don't know how anyone cannot defoliate, when dealing with so many fan leaves.
Personally I think you should give co2 a go, as you have a really dialed environment there, and your plants are very happy.
With my setup (see pic)
IMG 20200325 071439561 HDR
and the fact that CO2 settles to the floor, do you think I could pull it off? The room is 12X8.
 
ru knuts

ru knuts

254
63
Definitely.
Get a couple of floor fans that you can tilt up to face the ceiling, and your co2 will be moved back to where you want it.
Thanks, I just may give it a go on my next run, my clones will be ready before I harvest.
 
FourthCity

FourthCity

778
143
I'm more confused now. I have a remote thermostat/humidistat. It's hanging on the wall at canopy level, but ~4' from the middle of the canopy. I have 2 oscilating fans just above the canopy, one blowing under the canopy, a stationary fan blowing into the corner and a ceiling fan. I have an infrared thermostat I check the leaf temp, it's generally 1-2 degrees cooler than room temp. Room temp hovers 79-81. No added CO2.
I'm in early week 4 of flowering. My VPD, the way it's set up now ranges between 1.14 and 1.34 most of the day with lights on.
I want to think I'm doing this wrong. Any suggestions?
If you are in early to mid flower then you are just fine.
Okay that's cool.
I have the same issue with the jungle like overgrowth.
Honestly don't know how anyone cannot defoliate, when dealing with so many fan leaves.
Personally I think you should give co2 a go, as you have a really dialed environment there, and your plants are very happy.
Heavy defoliating defeats the purpose of adding co2 as it can only be absorbed by the leaves. I think you are both misunderstanding what I am saying about vpd and co2, if you are dialed in and managing the vpd correctly the leaf temps will tell you what the rest of the environment should be for optimum growth, regardless of whether or not you are using co2. You both may already have enough natural co2 in you grow area to meet your plants demands. Co2 is most beneficial for commercial scale growers with many plants that are consuming more co2 than what is available, it also helps the plants endure higher ambient temps. Commercial growers don't run their grows hot so they can use co2, they use co2 so they dont have to spend as much on cooling. It has its benefits but I have only seen a few growers on here with setups that appear capable of truly taking advantage of what co2 can offer. Most people I see using co2 appear to be wasting it and would be better of spending their resources on other parts of their grow.
 
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SupaC

SupaC

26
13
If you are in early to mid flower then you are just fine.

Heavy defoliating defeats the purpose of adding co2 as it can only be absorbed by the leaves. I think you are both misunderstanding what I am saying about vpd and co2, if you are dialed in and managing the vpd correctly the leaf temps will tell you what the rest of the environment should be for optimum growth, regardless of whether or not you are using co2. You both may already have enough natural co2 in you grow area to meet your plants demands. Co2 is most beneficial for commercial scale growers with many plants that are consuming more co2 than what is available, it also helps the plants endure higher ambient temps. Commercial growers don't run their grows hot so they can use co2, they use co2 so they dont have to spend as much on cooling. It has its benefits but I have only seen a few growers on here with setups that appear capable of truly taking advantage of what co2 can offer. Most people I see using co2 appear to be wasting it and would be better of spending their resources on other parts of their grow.
Thanks for this FC.
I completely understand where you are coming from.
My experience with defoliation carried out at the end of stretch, is that the plants will have time to re-leaf themselves to carry them through to the end.
What you say about defeating the purpose of co2 by not having enough leaf surface makes perfect sense.
As I am a grower of massive plants (by indoor standards), would you concur that some form of defoliation is needed to get light to the whole plant.? Perhaps a mild defoliation?
 
FourthCity

FourthCity

778
143
Thanks for this FC.
I completely understand where you are coming from.
My experience with defoliation carried out at the end of stretch, is that the plants will have time to re-leaf themselves to carry them through to the end.
What you say about defeating the purpose of co2 by not having enough leaf surface makes perfect sense.
As I am a grower of massive plants (by indoor standards), would you concur that some form of defoliation is needed to get light to the whole plant.? Perhaps a mild defoliation?
Ill send you a direct message, dont want to get this thread too much off the vpd topic.
 

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