THE TRUTH ABOUT WHAT VPD RANGE YOU SHOULD USE.

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newbplantgrower420

Well-Known Member
VPDs tough to follow. the leaf temps vary greatly in my rooms. i always assumed its -2F or -3F under my LEDs.

i just took a leaf temp with my gun rn in late bloom its -7F compared to air temp. 83F air temp 76F leaf temp.

My Govee temp gage and trolmaster hydro x temps are off by 2F alone. That just messes up the whole vpd chart cause is it -7F difference or -5F difference in leaf temp vs air temp.

not so black and white like these people make it seem.
 
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goofy81

Well-Known Member
Everyone caught up in VPD.
Transpiration rate is also affected by wind speed. Which is a lot easier for indoor growers to control.
There was a study I read long ago where good air circulation can increase the photosynthetic rate by 60%+ . Doubt anyone on the forum wants to read it but if they do feel free to PM and I'll find it.

Every single one of my rooms has ceiling fans.. Some with ceiling fans over 100 inches! I know it's hard for tent growers but that's the experience large hydroponic greenhouses also face.
 
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Stumay111

Active Member
goofy81 said:
Everyone caught up in VPD.
Transpiration rate is also affected by wind speed. Which is a lot easier for indoor growers to control.
There was a study I read long ago where good air circulation can increase the photosynthetic rate by 60%+ . Doubt anyone on the forum wants to read it but if they do feel free to PM and I'll find it.

Every single one of my rooms has ceiling fans.. Some with ceiling fans over 100 inches! I know it's hard for tent growers but that's the experience large hydroponic greenhouses also face.
Click to expand...
That's awesome info, and I agree with having great circulation!
 
vostok

vostok

Well-Known Member
goofy81 said:
Impossible for me most of the time to increase my VPD ( too much vegetation in room)
I never get rot (4 ceiling fans help)
And I haven't noticed a much steeper pot weight dip during summer temperatures with higher VPD.
I'm getting excellent yields (600gr/m2+) of extremely sticky bud too.
VPD is not the be all, end all people think.

I personally think WIND velocity is one of the most important ways to prevent rot and somehow affects VPD greatly too

Here's an interesting quote with source about VPD, it explains the plants find balance with high humidity.

"A dry environment will simply pull more transpiration out of the plant itself, drawn up through the roots. If the pressure imbalance goes on too long, and the atmosphere is too dry, plant's close off their stomata as a final protective mechanism to reduce moisture loss. "

"In a relatively humid environment, the VPD is low. The vapor pressure internally and externally even out. Finding a perfect balance of humidity and temperature, guarantees water and nutrient movement, but prevents aggressive waste seen in low relative humidity environments. Plants are generally less stressed, and more receptive to CO2 in the grow room."

SOURCE: https://www.cannabistech.com/articles/mastering-vpd-control-for-plentiful-harvests/


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Here's the perfect healthy plants in a low VPD environment. (taken just now as with the above graph)


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what gear are you recording them graphs on ...I'm looking for the same?

cheers
 
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Laythy

Member
my experience is dont chase numbers. set your desired temp and humidity for a vpd of 1 to 1.3 during all stages and if you stay at that rate you're golden but chances are you're going to fluctuate no matter what, day vs night watering day vs skip day and so on.

i set my temp at 83 and humidity at 60 and have no issue other than humidity shoot up to 80% or more during light off. i still dont have an issue per say because do we really care about vpd during lights off or just light on? maybe someone will have an answer to that and shed some light.
 
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newbplantgrower420

Well-Known Member
Laythy said:
my experience is dont chase numbers. set your desired temp and humidity for a vpd of 1 to 1.3 during all stages and if you stay at that rate you're golden but chances are you're going to fluctuate no matter what, day vs night watering day vs skip day and so on.

i set my temp at 83 and humidity at 60 and have no issue other than humidity shoot up to 80% or more during light off. i still dont have an issue per say because do we really care about vpd during lights off or just light on? maybe someone will have an answer to that and shed some light.
Click to expand...
I kept my VPD at ~1kPa this whole 8 week veg run. I usually drop the humidity late in veg to higher the kPa and avoid pm but didnt get any pm so going to keep keeping at ~1 from now on. 85F and 70% humidity

Im going to try keeping it at ~1 this whole flower run hopefully I dont get bud rot or pm. lets see if theres a yield difference. probably something like 82F 65% hum lights on and 75F 60% hum lights off. but my humidity also spikes like urs right when lights turn off..... i cant really fix that sadly.
 
Three Berries

Three Berries

Well-Known Member
First year of a tent grow and monitoring temp humidity. So far it has all been temp control during summer at 84F. Humidly got high at lights off though. When it hit 80% I turned on the exhaust. Now that fall is here it seems to run just a bit wet , <.80 and when lights on ~.80-.90, with both exhaust fans running all the time. It will be interesting as the winter cold sets in to see how it goes. I never really worried about it before, just kept an exhaust fan running all the time and a soil thermometer that would run in the mid to upper 60Fs.
 
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