Does Vpd Matter At Night?

  • Thread starter StandingRock
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StandingRock

StandingRock

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I'm going to go with no it doesn't matter. VPD is all about how the stomata interacts with the atomospheric conditions. If stomata are closed then VPD has no effect.
 
StandingRock

StandingRock

334
93
I'm asking because if I just let my dehuey and humidifier and ac just do whatever they want at night that would save me some energy. Usually the ac pulls the humidity down to about 50%. Not bad but I wouldn't want that during lights on.
 
CaliRooted

CaliRooted

1,536
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Second that great question. I follow VPD as close as I can up until week 6 of flower. VPD numbers start to freak me out when my colas start getting large, then it's back to 50% humidity.
 
whitepistols

whitepistols

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63
Here is a simple answer for you, and for the record vpd is tightly used when I run.

So my answer is this. When your lights go off check your humidty every hour for 4 hrs see what you find out. It may surprise you.

You need to know the peaks and falls of your humidity. Yes you dont need to dehuyey every hour of lights off ac may keep up, but those first 5 hours, well theres alot going on.

Dialing in means you know, and control every detail. Alot use Jungle boys as vpd referance. Look up Jackmayoffer on google pick your forum. Its the same person. He preached it many scoffed at vpd. When people started using it religiously is when gpw was not even discussed, it become #'s per light.

Granted 1 bulb is pissing in the wind if after weight, you need multipul light point sources and a honest heavy yeilder. Dont forget a 4 to 5 foot tall plant trained heavly.
 
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R

ROOBIX

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At night when stomata are closed and the plant isn't uptaking does the VPD matter at all?
True, transpiration is not important at night. I like to follow vpd at night because it makes the transition to day vpd more natural. For a sealed room this is more imoprtant as your equipment doesnt get taxed as hard at lights on to make the right environment. If you have high rh at lights on, rh may get too high as the temp comes up and a dehuey cant keep up, especially as it os adding jeat to the room. Ac kicks on, pulls too much ater out, and the sustems continue to fight eachother.
Also getting dry woth low temps along with good air circulation will prevent mold from high rh day cycles.
Sorry, blunt of nyc diesel made me ramble.
 
R

ROOBIX

63
18
Stoner translation:
os=is
jeat=heat
ater=water
sustems=systems
woth=at night with
Oh and if you have cooling fans on your lights, especially cool tubes, put em on speed controllers, and use a timer to dial in your rise and fall of temp. Flushing the hps heat for 10 min into dark can ease the nightime temp transition on the rest of your equipmemt.
At lights on, I let my lights run for 15 min (tweakable) before the fans come on to use the lights to heat the room. This is especially useful if seasonal changes affect your room performance. Winter time my fans barely move to provide room heat and prevent cool tube overheating.
 
B

billymirage

5
1
At night when stomata are closed and the plant isn't uptaking does the VPD matter at all?
During the night, plants still perform respiration, or in other words – breathe. This means that they open their stomate and release CO2, which causes water to evaporate.

While there’s no photosynthesis occurring, night time respiration still plays an important role in plant growth.
 
Observationist

Observationist

5,320
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I'm asking because if I just let my dehuey and humidifier and ac just do whatever they want at night that would save me some energy. Usually the ac pulls the humidity down to about 50%. Not bad but I wouldn't want that during lights on.
My hum is on my light timer
 
PulsePeet

PulsePeet

Supporter
75
53
Did some research on this, to sum it up:
VPD at night isn't nearly as important as your day VPD, it's still an important factor to consider for vigorous plant growth and increased yields

I've got an update all about night time VPD here on my blog if you wanna learn more: VPD AT NIGHT
 
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