Gassing with Co2 and following VPD chart.

So much different information I have seen and heard.

Lets try again to bring up the discussion please.

So I'm using CO2 at 1300ppm.

1) What temp/RH or VPD value should I be following for maximum CO2 efficiency? .. and for how many weeks in flowering? As I understand at one point RH should be lowered to prevent powdery mildew appearance.
Maybe some experienced grower could lay out what temp and RH he uses at certain weeks throughout flowering? - would be very nice.

2) Another question - where is the temperature measured - is it inside the canopy in shade? Under canopy? And if using as high temperatures as recommended in VPD chart, I see a possible problem towards affecting the rootzone negatively. What might be the upper limit for the actual rootzone(inside the pot) before temperature starts being a problem?

I think that's everything I need to know.

I hope to see some activity in this thread

And please don't be mad at me for asking these questions.

Helmut79 said:

So much different information I have seen and heard.

Lets try again to bring up the discussion please.

So I'm using CO2 at 1300ppm.

1) What temp/RH or VPD value should I be following for maximum CO2 efficiency? .. and for how many weeks in flowering? As I understand at one point RH should be lowered to prevent powdery mildew appearance.
Maybe some experienced grower could lay out what temp and RH he uses at certain weeks throughout flowering? - would be very nice.

2) Another question - where is the temperature measured - is it inside the canopy in shade? Under canopy? And if using as high temperatures as recommended in VPD chart, I see a possible problem towards affecting the rootzone negatively. What might be the upper limit for the actual rootzone(inside the pot) before temperature starts being a problem?

I think that's everything I need to know.

I hope to see some activity in this thread

And please don't be mad at me for asking these questions.

Click to expand...

Ya you need to ignore that chart and members that use or think it works

Helmut79 said:

So much different information I have seen and heard.

Lets try again to bring up the discussion please.

So I'm using CO2 at 1300ppm.

1) What temp/RH or VPD value should I be following for maximum CO2 efficiency? .. and for how many weeks in flowering? As I understand at one point RH should be lowered to prevent powdery mildew appearance.
Maybe some experienced grower could lay out what temp and RH he uses at certain weeks throughout flowering? - would be very nice.

2) Another question - where is the temperature measured - is it inside the canopy in shade? Under canopy? And if using as high temperatures as recommended in VPD chart, I see a possible problem towards affecting the rootzone negatively. What might be the upper limit for the actual rootzone(inside the pot) before temperature starts being a problem?

I think that's everything I need to know.

I hope to see some activity in this thread

And please don't be mad at me for asking these questions.

Click to expand...

I try to hit 81 degrees with high 50's rh and roughly 900ppm of co2. I gas from last week of veg till about week 7 of 9 during flower which i bring the ppm's back down to 420ppm.
Ive tried following the VPD chart, even went as far as getting a commercial fogger to up the rh. For me it was too much water around leaf surfaces and it showd in the plants. I wouldn't do it.

a mongo frog said:

I try to hit 81 degrees with high 50's rh and roughly 900ppm of co2. I gas from last week of veg till about week 7 of 9 during flower which i bring the ppm's back down to 420ppm.
Ive tried following the VPD chart, even went as far as getting a commercial fogger to up the rh. For me it was too much water around leaf surfaces and it showd in the plants. I wouldn't do it.

Click to expand...

Where is the temperature measured - is it inside the canopy in shade? Under canopy? What might be the upper limit for the actual rootzone (inside the pot) before temperature starts being a problem?

Come on, people where are all the big growers?

I'm definitely not a big grower...

If you follow the VPD charts, they are going off of leaf surface temperature (LST). You don't measure the air at all.

Depending on what your light source is, the lst can change.

HID lighting will have a higher LST than an LED with the same ambient temperatures because it puts out more IR, which heats the leaves beyond ambient..

https://www.blackdogled.com/lst
That is a good read.

To find your optimum temp I would personally get my co2 where I want it, then raise the heat 2 degrees a day until I see some slight heat stress. Then back down the temps a few degrees. Keep humidity in check as you do this. Remember, RH will go down when heat goes up with the same amount of water in the air.

If I'm not mistaken, the higher temperature used to increase metabolism will uptake more CO2 and growth is faster. That isn't dependent on RH/VPD. But once you get to the optimum temp for the CO2, you can then adjust for VPD (if following the charts).

Keep in mind, changing the VPD will change transpiration rates. So if you make it dryer (relatively), the plant will drink and "sweat" more. With every sip it brings along nutrients with it. The more sips, the more nutes build up. If you lower the VPD the plant will transpire less and will get less nutes than if it were transpiring more.

I'm jabbering... stoned...

friedguy said:

I'm definitely not a big grower...

If you follow the VPD charts, they are going off of leaf surface temperature (LST). You don't measure the air at all.

Depending on what your light source is, the lst can change.

HID lighting will have a higher LST than an LED with the same ambient temperatures because it puts out more IR, which heats the leaves beyond ambient..

https://www.blackdogled.com/lst
That is a good read.

To find your optimum temp I would personally get my co2 where I want it, then raise the heat 2 degrees a day until I see some slight heat stress. Then back down the temps a few degrees. Keep humidity in check as you do this. Remember, RH will go down when heat goes up with the same amount of water in the air.

If I'm not mistaken, the higher temperature used to increase metabolism will uptake more CO2 and growth is faster. That isn't dependent on RH/VPD. But once you get to the optimum temp for the CO2, you can then adjust for VPD (if following the charts).

Keep in mind, changing the VPD will change transpiration rates. So if you make it dryer (relatively), the plant will drink and "sweat" more. With every sip it brings along nutrients with it. The more sips, the more nutes build up. If you lower the VPD the plant will transpire less and will get less nutes than if it were transpiring more.

I'm jabbering... stoned...

Click to expand...

Youve been reading too much led troll and paste science and not done your homework here dude....

"In terms of energy, sunlight at Earth's surface is around 52 to 55 percent infrared (above 700 nm), 42 to 43 percent visible (400 to 700 nm), and 3 to 5 percent ultraviolet (below 400 nm). "

I tell ya this white trash science and led trolling needs to stop here

Helmut79 said:

Where is the temperature measured - is it inside the canopy in shade? Under canopy? What might be the upper limit for the actual rootzone (inside the pot) before temperature starts being a problem?

Click to expand...

Your running Co2 trying to Vpd and you dont know where to place a thermometer...

Ya yiu running waaay before you learnt to walk

I go for 86-94 ( 94 under the lamp 86 outer canopy) leaf temp at the canopy 40-45 rh at 1300 ppm ( would prefer 900ppm but controller is set to 1300.... oh well lol) only worry about vpd in veg.

Kingrow1 said:

Youve been reading too much led troll and paste science and not done your homework here dude....

"In terms of energy, sunlight at Earth's surface is around 52 to 55 percent infrared (above 700 nm), 42 to 43 percent visible (400 to 700 nm), and 3 to 5 percent ultraviolet (below 400 nm). "

I tell ya this white trash science and led trolling needs to stop here

Click to expand...

Dude... I've grown for some time. My family had a 5 acre outdoor farm for 5 years and grew medium scale indoors for about a decade. Ive grown on and off for about 15 years. I've grown hydro, soil, organic, indoors, out, co2, with hid, fluorescent and led. I've been around the block once or twice and have done plenty "homework". And the "white trash" comment is plain racist.

Yes the sun puts out a lot of ir. No shit. Led doesn't normally put out much. Hid puts out more ir than led. No shit.

I think the led spectra that most use is incomplete. Its missing uv and ir and more.

I personally don't follow vpd charts. I do use it as somewhat of a baseline, only theres no way id have it that humid, personally, especially after stretch.

I don't know what the fuck you are talking about led trolling. I don't endorse any one grow method. Nor do I have any gripes with the major grow lighting types. Ive use most types, all successfully. All seem to have benefits and problems.

Follow the vpd charts or not. I like rh lower that most charts suggest. Raise temps for co2.

friedguy said:

Dude... I've grown for some time. My family had a 5 acre outdoor farm for 5 years and grew medium scale indoors for about a decade. Ive grown on and off for about 15 years. I've grown hydro, soil, organic, indoors, out, co2, with hid, fluorescent and led. I've been around the block once or twice and have done plenty "homework". And the "white trash" comment is plain racist.

Yes the sun puts out a lot of ir. No shit. Led doesn't normally put out much. Hid puts out more ir than led. No shit.

I think the led spectra that most use is incomplete. Its missing uv and ir and more.

I personally don't follow vpd charts. I do use it as somewhat of a baseline, only theres no way id have it that humid, personally, especially after stretch.

I don't know what the fuck you are talking about led trolling. I don't endorse any one grow method. Nor do I have any gripes with the major grow lighting types. Ive use most types, all successfully. All seem to have benefits and problems.

Follow the vpd charts or not. I like rh lower that most charts suggest. Raise temps for co2.

Click to expand...

Leaf surface temperature - no matter what the ir the plant will regulate to exactly the same temperature led hps cmh t5 if it is healthy and not limited. It has been pointed out that its temperature is always in flux so your reading nothing you understand.

This lst rubbish comes from led troll stuff... ohh i see you did include the blackdog hype (er) link lol

Where do you go with Vpd if you havent made a proper equation. The simplistic vpd chart is not for a leaf but a surface in still air, derived from equations on simple vapour pressure freely explained on wiki.

Factor in the wind plus the distinction in species between your leaf morphology and boundary layer plus stomata density plus a few more readings like inner leaf temp and such and yer were starting to get some where.

Next we want to check the plant actually transports enough water daily with a few probes, connect to a computer and real time automate light intensity humidity heat and soil temps.

I forget were growing weed, feels more like some hi tech industry like what vpd is used for

Helmut79 said:

So much different information I have seen and heard.

Lets try again to bring up the discussion please.

So I'm using CO2 at 1300ppm.

1) What temp/RH or VPD value should I be following for maximum CO2 efficiency? .. and for how many weeks in flowering? As I understand at one point RH should be lowered to prevent powdery mildew appearance.
Maybe some experienced grower could lay out what temp and RH he uses at certain weeks throughout flowering? - would be very nice.

2) Another question - where is the temperature measured - is it inside the canopy in shade? Under canopy? And if using as high temperatures as recommended in VPD chart, I see a possible problem towards affecting the rootzone negatively. What might be the upper limit for the actual rootzone(inside the pot) before temperature starts being a problem?

I think that's everything I need to know.

I hope to see some activity in this thread

And please don't be mad at me for asking these questions.

Click to expand...

hey mate, im gathering some info around the web for my automation system, ill share some resources i have with you... im not going to respond to spite and jokers, its enough i know they have to live with themselves

anyway, vpd really is a thing, showing promise with not only cannabis, but other plants like tomatoes and chillies... well, you have to measure temperature of air around the plants (so in canopy level, it wont help much if you measure temps around your lamp), AND you have to measure your leaves temps, i would suggest handheld IR thermometer for that, because we are measuring difference of air vapor saturation and leaf vapor saturation, and that is the vapor pressure deficit we want to have so that our plants can transpire as much as they can without any stress... a good chart, which takes into account your leaf temp (but it looks ugly), can be found here:


a good info about vpd i have found here:


and good info about temps and other with using co2 i have found here:


especially pdf from fluence... i would also suggest going entirely on overgrow forum, you wont find any of the asses that show up here, community is open, respectable, and knowledgeable... wish you all the best, happy growing! <3

Ahhh kingrow and his 13” autoflowers. Miss that guy.

pahval said:

hey mate, im gathering some info around the web for my automation system, ill share some resources i have with you... im not going to respond to spite and jokers, its enough i know they have to live with themselves

anyway, vpd really is a thing, showing promise with not only cannabis, but other plants like tomatoes and chillies... well, you have to measure temperature of air around the plants (so in canopy level, it wont help much if you measure temps around your lamp), AND you have to measure your leaves temps, i would suggest handheld IR thermometer for that, because we are measuring difference of air vapor saturation and leaf vapor saturation, and that is the vapor pressure deficit we want to have so that our plants can transpire as much as they can without any stress... a good chart, which takes into account your leaf temp (but it looks ugly), can be found here:

VPD Calculator by Everest Fernandez

a good info about vpd i have found here:

and good info about temps and other with using co2 i have found here:

Factors that influence growth and development ( Temp and VPD)

I’ve uploaded the Fluence guide before, here’s the complete version Fluence Bioengineering_High PPFD Cultivation Guide_v1.2.pdf (1.4 MB) another good one! Lumigrow LumiGrow_LED_Growers_Guide_for_Cannabis.pdf (2.0 MB) and not to be outdone…Illumitex…we got 'em all here at OG...

overgrow.com

especially pdf from fluence... i would also suggest going entirely on overgrow forum, you wont find any of the asses that show up here, community is open, respectable, and knowledgeable... wish you all the best, happy growing! <3

Click to expand...

This thread is old lol
But, Ill still add my 2 cents.
I use these charts to get an optimal environment







and here is a helpful flow chart for hydro water

Helmut79 said:

So much different information I have seen and heard.

Lets try again to bring up the discussion please.

So I'm using CO2 at 1300ppm.

1) What temp/RH or VPD value should I be following for maximum CO2 efficiency? .. and for how many weeks in flowering? As I understand at one point RH should be lowered to prevent powdery mildew appearance.
Maybe some experienced grower could lay out what temp and RH he uses at certain weeks throughout flowering? - would be very nice.

2) Another question - where is the temperature measured - is it inside the canopy in shade? Under canopy? And if using as high temperatures as recommended in VPD chart, I see a possible problem towards affecting the rootzone negatively. What might be the upper limit for the actual rootzone(inside the pot) before temperature starts being a problem?

I think that's everything I need to know.

I hope to see some activity in this thread

And please don't be mad at me for asking these questions.

Click to expand...

Great discussion thread.

I'm not a 'big grower' but since I began indoor Sept 2020, I have become somewhat 'addicted' and have transformed own from an single room 'open loop system' to 3 rooms (1300 cu ft) 'hybrid loop system'.

I have read a lot on other RIU threads regarding open loop, closed loop, and hybrid loop systems. And I truly believe this hybrid type design is most ideal to chasing the elusive VPD especially for those living in colder/dryer climates like myself in SF Bay Area minimizing fossil fuel/costs of mini split versus cool fresh air intake using carbon,, charcoal,, insect,, heppa filters,, and dampers. Outaking hot/stale air from grow room to grow room (ideally located right next or near eachother).

I am understanding that VPD needs to be between 0.8 kPa to 1.1 kPa during veg and 1.1 kPa to 1.5kPa ....is this correct?

I am also in search of answers re best temps/RH & corresponding vpd especially during week 3 of veg growing a 60/40 hybrid gelato 41 bc I also thought landrace genetics had a lot to do with vpd (temp/rh) too, should I raise my temps but keep RH around 65% or 70% , and start lowering to 50% then 40% then last wk flower 35%....?.


I've automated my grow best i could using multiple different hygrometer, sensors, controllers, timers,

Open to any feedback or questions re my hybrid loop system .

Cheers

So you dont know what are talking about. Leds dont get as hot as hid hps lights because they produce more ir. And he is correct about vpd as well. And the blackdog article is science based and relevant.any cultivator greenhouse grower worth anything knows leaf surface temp and ambient temp are often different depending on the light source

Kingrow1 said:

Leaf surface temperature - no matter what the ir the plant will regulate to exactly the same temperature led hps cmh t5 if it is healthy and not limited. It has been pointed out that its temperature is always in flux so your reading nothing you understand.

This lst rubbish comes from led troll stuff... ohh i see you did include the blackdog hype (er) link lol

Click to expand...

Broclee said:

So you dont know what are talking about. Leds dont get as hot as hid hps lights because they produce more ir. And he is correct about vpd as well. And the blackdog article is science based and relevant.any cultivator greenhouse grower worth anything knows leaf surface temp and ambient temp are often different depending on the light source

Click to expand...

Hes been banned for well over a year now

Broclee said:

So you dont know what are talking about. Leds dont get as hot as hid hps lights because they produce more ir. And he is correct about vpd as well. And the blackdog article is science based and relevant.any cultivator greenhouse grower worth anything knows leaf surface temp and ambient temp are often different depending on the light source

Click to expand...

bk78 said:

Hes been banned for well over a year now

Click to expand...

Lol with good reason i suppose lolol

Kingrow1 said:

Leaf surface temperature - no matter what the ir the plant will regulate to exactly the same temperature led hps cmh t5 if it is healthy and not limited. It has been pointed out that its temperature is always in flux so your reading nothing you understand.

This lst rubbish comes from led troll stuff... ohh i see you did include the blackdog hype (er) link lol

Click to expand...

You obviously haven't grown with LED. And you obviously don't know about IR either. Infrared is totally unusable by the plant it just heats up the surface of the leaf hid and CMH and fluorescent all have IR LED without separate IR diodes has none. So therefore any type of light with ir will make a warmer leaf surface temperature. And for proper VPD measurement you measure the leaf surface temp the air temp and the relative humidity. Trying to troll when you don't know what you're talking about is hilarious.