VPD HELPING??

S

silk689

Well-Known Member
Hey everyone just getting some feedback and doing some market research on what you think of VAPOUR PRESSURE DEFICIT (VPD) charts? Do you follow the charts? And has it made a difference to your plants?

iam not asking you to convince me coz i always dial it into my environment, but rather what your thoughts are towards it :-))

The charts i use are from “Pulse”:)
 
DoubleAtotheRON

DoubleAtotheRON

Well-Known Member
All the way till the end... currently in week 12, 83 degrees/63% Rh. No mold, but I do use an AirROS system.... and it works. If I didn't have an AirROS, I would venture off of the VPD chart mid flower..... because I have failed labs before without it. Lost my ass on a crop. But yes, it does create better yields, healthy growth following VPD.
 
ZookieBoy

ZookieBoy

Member
silk689 said:
Spot on man 8) i do EXACTLY the same and even go to 30% humidity in the last week. Thanx 4 replying brother
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I have a question cause during lights on obviously my rh is lower then at night. Can get it below 40 during lights on (35-40) if I want (have been using a humidifier on an ink bird) to keep it a little higher, now am on week 7 and no matter what I do during lights off it’s always higher. Is it ok if during lights off it gets up to 40-45 ? My duhu pumps out crazy hot air so I try not to turn that on during lights off unless i feel like I have to cause it can get it warmer then when lights are on lol. (Above 80) Ik you usually want it even drier during lights off as they aren’t photosynthesizing and there’s no pressure on the plant. I’m wondering if I just want it all dry as possible even if it’s a little higher rh during lights off I’m fully venting and fans on high when it’s night time and during the day turn it down slightly. Any help would be great
 
calvin.m16

calvin.m16

Well-Known Member
Always remember for a proper VPD measurement you need to account LST (Leaf Surface Temperature) either subtracting or adding it to the air temp depending if the leaves are hotter or colder. Lots of those charts aren't accounting Leaf Surface Temps. If your air is 75 °F and your bud is 80 °F and you look at the chart without factoring the LST you will be way off on your kPa reading.
 
ZookieBoy

ZookieBoy

Member
I have a temp gun and currently use
vpdchart.com

VPD Chart

Vapor pressure deficit (VPD) chart & calculator for horticulture in controlled environment. Cannabis, tomatoes, leafy greens, cucumber.
vpdchart.com vpdchart.com
 
ZookieBoy

ZookieBoy

Member
ZookieBoy said:
I have a temp gun and currently use
vpdchart.com

VPD Chart

Vapor pressure deficit (VPD) chart & calculator for horticulture in controlled environment. Cannabis, tomatoes, leafy greens, cucumber.
vpdchart.com vpdchart.com
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Have heard a lot of ppl Ditch vpd the last week and just want it dry as possible so the plant produces as much secondary metabolites as possible. But find the rh is always a little higher during lights off if I do so. So I’m wondering if that should be a concern. Because I’m still keeping it below 45 at night. Just during lights on much easier to dry it out in there yk, and to that my humidifier will turn on quite often and Ik w humidifier going off all day in my lung room isn’t really what the plants need in the last week. Or is it ? Have an ac infinity s4 going 24/7 for plant health and what not
 
HydroKid239

HydroKid239

Well-Known Member
ZookieBoy said:
I have a question cause during lights on obviously my rh is lower then at night. Can get it below 40 during lights on (35-40) if I want (have been using a humidifier on an ink bird) to keep it a little higher, now am on week 7 and no matter what I do during lights off it’s always higher. Is it ok if during lights off it gets up to 40-45 ? My duhu pumps out crazy hot air so I try not to turn that on during lights off unless i feel like I have to cause it can get it warmer then when lights are on lol. (Above 80) Ik you usually want it even drier during lights off as they aren’t photosynthesizing and there’s no pressure on the plant. I’m wondering if I just want it all dry as possible even if it’s a little higher rh during lights off I’m fully venting and fans on high when it’s night time and during the day turn it down slightly. Any help would be great
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Is the dehumidifier in the room the tent is in.. or the tent? I believe it should be outside the tent.. unless you are pulling in air from outside? Venting out into the room & sucking the same air back in?
 
ZookieBoy

ZookieBoy

Member
HydroKid239 said:
Is the dehumidifier in the room the tent is in.. or the tent? I believe it should be outside the tent.. unless you are pulling in air from outside? Venting out into the room & sucking the same air back in?
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It’s outside the tent but the tent is just in a room. Therefore making my lung room super warm during lights off.
 
ZookieBoy

ZookieBoy

Member
HydroKid239 said:
Nothing wrong with warmth at lights off. If anything turn it off, or set it to kick on when RH hits 55%.
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But I’m saying during lights on it can get down to 40 and below but lights off can stay around 45 -50 with no dehu and Ik you want it dryer during lights off. Do I just do the best I can at drying it out ? Or should I still use humidity during lights on currently 80* with around 77 leaf temp def warmer then I’d like during the last week but the light is raised and dimmed. Not sure if over drying during lights on is going to cause problems especially if it’s a higher rh during lights off. A little backwards right ?
 
HydroKid239

HydroKid239

Well-Known Member
ZookieBoy said:
But I’m saying during lights on it can get down to 40 and below but lights off can stay around 45 -50 with no dehu and Ik you want it dryer during lights off. Do I just do the best I can at drying it out ? Or should I still use humidity during lights on currently 80* with around 77 leaf temp def warmer then I’d like during the last week but the light is raised and dimmed. Not sure if over drying during lights on is going to cause problems especially if it’s a higher rh during lights off. A little backwards right ?
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For the most part of my grows in flower my night rh was always higher than the day. It’s spiked on me.. and still turned out ok. Just keep watch for PM. Keep good air flow 24/7. Minimize leaf on leaf contact. Those things can help prevent PM, tho it’s not a bulletproof scheme.
 
PadawanWarrior

PadawanWarrior

Well-Known Member
My VPD is way off. It would be better if it was lower but I haven't added a controller to control my outside fan. I have one sitting here somewhere though.

My RH is around 10% since I'm constantly venting outside and I'm in CO. It does stress the plants out a bit, and they can burn more easily with nutrients. And are definitely more prone to nanners. But it can be done.

It's also way more difficult to clone.
 
ZookieBoy

ZookieBoy

Member
PadawanWarrior said:
My VPD is way off. It would be better if it was lower but I haven't added a controller to control my outside fan. I have one sitting here somewhere though.

My RH is around 10% since I'm constantly venting outside and I'm in CO. It does stress the plants out a bit, and they can burn more easily with nutrients. And are definitely more prone to nanners. But it can be done.

It's also way more difficult to clone.
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Yea 10% sounds rough lol but you don’t use a humidifier during flower at all? And your night rh spikes I’m guessing lol
 
PadawanWarrior

PadawanWarrior

Well-Known Member
ZookieBoy said:
Yea 10% sounds rough lol but you don’t use a humidifier during flower at all? And your night rh spikes I’m guessing lol
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No humidifier or anything. And my dark period is the same since I'm constantly exhausting outside. But the dark period is the more humid time even though it's still usually around 10%.

Like I said it's not ideal, but it can work.
 
King Avitas

King Avitas

Well-Known Member
I am running 0.9-1kPa in my room. Temp is 90⁰f, humidity at 74% and LST is -2⁰f.

Btw I am running CO² hence the high temps.

But the plants are loving it, especially the stomata...
IMG_20220325_025035.png
 
S

silk689

Well-Known Member
ZookieBoy said:
I have a question cause during lights on obviously my rh is lower then at night. Can get it below 40 during lights on (35-40) if I want (have been using a humidifier on an ink bird) to keep it a little higher, now am on week 7 and no matter what I do during lights off it’s always higher. Is it ok if during lights off it gets up to 40-45 ? My duhu pumps out crazy hot air so I try not to turn that on during lights off unless i feel like I have to cause it can get it warmer then when lights are on lol. (Above 80) Ik you usually want it even drier during lights off as they aren’t photosynthesizing and there’s no pressure on the plant. I’m wondering if I just want it all dry as possible even if it’s a little higher rh during lights off I’m fully venting and fans on high when it’s night time and during the day turn it down slightly. Any help would be great
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1 - firstly how many weeks flowering does your strain go to?

2 - try to stabilise your temp to 75%f dead on if you can. Does ur led lights allow u to turn it down a tad bit more?

3 - since you have a dehumidifier, is it a digital one? If so during lights on, program it to hit 35% dead on as ur in week 7. No higher then that.

4 - dont worry too much about ur RH when lights are off IF you can do the above i am suggesting. You said you have fans running thats moving air around which is good.

5 -pull off any fan leaves thats causing the canopy to be crowded so air circulates better.

6 - Always stop using the VPD chart AFTER week 4 of flowering. It will throw u off sync with high humidity numbers it suggests.
 
ZookieBoy

ZookieBoy

Member
silk689 said:
1 - firstly how many weeks flowering does your strain go to?

2 - try to stabilise your temp to 75%f dead on if you can. Does ur led lights allow u to turn it down a tad bit more?

3 - since you have a dehumidifier, is it a digital one? If so during lights on, program it to hit 35% dead on as ur in week 7. No higher then that.

4 - dont worry too much about ur RH when lights are off IF you can do the above i am suggesting. You said you have fans running thats moving air around which is good.

5 -pull off any fan leaves thats causing the canopy to be crowded so air circulates better.

6 - Always stop using the VPD chart AFTER week 4 of flowering. It will throw u off sync with high humidity numbers it suggests.
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sorry I am 50 days in so just finished week 7 and the strains I’m running are done at week 8-9 . Is my first indoor grow so looking to pull asap I dimmed the light back to ab 50% and have it over a ft away. It’s a SE3000 nothing crazy. I have temps down now to around 77 lst -2. It is digital but the problem is it creates super hot air I’m talking above 90* which is way too hot for how mild it dumidifies so during lights off I try and use it only when it gets over 40. But your recommending 35% or lower during lights on ? And then just do the best I can about rh during lights off ? I don’t have a problem getting lower rh during lights on I just have been using a humidifier in my lung room to help keep it around 40 .. cause keeping my tent extra dry during lights on and more humid during lights off seems backwards to me or am I off ?
 
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