VPD = PAIN

GemGrows24

GemGrows24

Member
Jimski said:
The biggest issue with chasing vdp is that due to sensor drift and sensor calibration issues most growers will be using false data to set limits in their environments. Out of the box most temp sensors have a +-2 degrees. From my own experience I calibrate my temp and RH sensors as often as my ph/ec tools. I do have an ACi system that is set to adjust to a constant vdp target but doing this means I only have to change temps for nighttime as the RH is adjusted by the controller.
Also do not sweat leaf temps. As soon as someone on RIU explains how they can zero point 2 sensors that use 2 different methods of measuring temps and that state ON THE BOX they are +-1 degree variable how they get useable data to set a leaf variance. At that point I will steal that idea and use it but right now I am not convinced.
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I'm personally not to stressed about VPD but do pay attention. after all the good feedback. I don't think my Vivosun smart grow system has the option to auto adjust the humidity to be in relative range for VPD. But it does its own calculations via probe. I adjust humidity levels myself according to the temp via probe . although I'm not to stressed on a Temp gun. I Still wanna grab one in the near future just so I can learn something . I think being able to understand how to calculate it manually could help me further understand VPD. I'm eager for Education and furthering my knowledge. But I'm also on a budget too.so I apologize for my attitude on the forum earlier. I just don't appreciate being made fun of without some further knowledge or facts to back it up.i don't mind being told I made a mistake or what I did was stupid but at least further explain so I can get something out of it lol.. I'm younger so getting all this equipment isn't as easy for me to get. So I really appreciate your comment and possibly understanding of my frustration.
 
Jimski

Jimski

Well-Known Member
GemGrows24 said:
I'm personally not to stressed about VPD but do pay attention. after all the good feedback. I don't think my Vivosun smart grow system has the option to auto adjust the humidity to be in relative range for VPD. But it does its own calculations via probe. I adjust humidity levels myself according to the temp via probe . although I'm not to stressed on a Temp gun. I Still wanna grab one in the near future just so I can learn something . I think being able to understand how to calculate it manually could help me further understand VPD. I'm eager for Education and furthering my knowledge. But I'm also on a budget too.so I apologize for my attitude on the forum earlier. I just don't appreciate being made fun of without some further knowledge or facts to back it up.i don't mind being told I made a mistake or what I did was stupid but at least further explain so I can get something out of it lol.. I'm younger so getting all this equipment isn't as easy for me to get. So I really appreciate your comment and possibly understanding of my frustration.
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I started with a vivosun tent kit for $309 that my wife bought me. I doubled the light it came with and added the ACI controller and the 2 magic boxes for heat and humidity. I love having 2 apps running that just about say the same thing and when they have a variance I fix it. This is now a fun hobby for me but as a new grower I started with hydro and had some problems. The first grow crashed and I decided to try soil and I am loving it.
I am an old dude who has been on forums since prodigy and you have no idea what that is but it tells you how old I am LOL. Belong to the iATN system for almost 30 years but do not post much but I think I had 20k posts on fixing cars and running auto shops. Places like this are awesome.
Good luck on the grow and anything I can help with pm me.
 
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Delps8

Well-Known Member
GreenGenez421 said:
Your forgetting about the leaf temperature offset. It's a critical input to calculating VPD. Without it, what's the point of monitoring VPD?
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I didn't include it because it would have been a distraction from the point I was trying to make which is that growers have attached a huge amount of mystery to VPD when all it is is one number instead of two.

GreenGenez421 said:
I will agree with you however that VPD is the cause of alot of nutrient issues. But this is because a sizable chunk of growers can't control it properly. If you could, you'd know.... it will take your grow to the next level.
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VPD is not an end in itself. It's a number that tells you how much water is leaving your plant. The key point is that if VPD is stupid high, your plants are going to be taking up a lot of water and, if you don't adjust nutrient strength, you might have nutrient issues.

I can't control the VPD in my grow tent but I can influence it and that's fine because, unless your VPD is waaaay out of bounds, it's not that important.

Other than that, for my purposes, if you can get VPD to 1.0 in veg and 1.2-1.4 in flower that's great but the bigger guardrail in flower is flower tops <78° and keep RH in the 40's or 50's.
 
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Delps8

Well-Known Member
GemGrows24 said:
I'm personally not to stressed about VPD but do pay attention. after all the good feedback. I don't think my Vivosun smart grow system has the option to auto adjust the humidity to be in relative range for VPD. But it does its own calculations via probe. I adjust humidity levels myself according to the temp via probe . although I'm not to stressed on a Temp gun. I Still wanna grab one in the near future just so I can learn something . I think being able to understand how to calculate it manually could help me further understand VPD. I'm eager for Education and furthering my knowledge. But I'm also on a budget too.so I apologize for my attitude on the forum earlier. I just don't appreciate being made fun of without some further knowledge or facts to back it up.i don't mind being told I made a mistake or what I did was stupid but at least further explain so I can get something out of it lol.. I'm younger so getting all this equipment isn't as easy for me to get. So I really appreciate your comment and possibly understanding of my frustration.
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The best source of info I've seen on VPD is here, on the Pulse Grow website. I used their gear at first but have gone through three complete generations of equipment and am using, and recommend, equipment from AC Infinity.

Re. calculating VPD-the Pulse site will give you the background on VPD as well as a spreadsheet to do the calculations. As an avid Excel user, I started in 1987, that's a good way to.
 
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GreenGenez421

Well-Known Member
Delps8 said:
I didn't include it because it would have been a distraction from the point I was trying to make which is that growers have attached a huge amount of mystery to VPD when all it is is one number instead of two.


VPD is not an end in itself. It's a number that tells you how much water is leaving your plant. The key point is that if VPD is stupid high, your plants are going to be taking up a lot of water and, if you don't adjust nutrient strength, you might have nutrient issues.

I can't control the VPD in my grow tent but I can influence it and that's fine because, unless your VPD is waaaay out of bounds, it's not that important.

Other than that, for my purposes, if you can get VPD to 1.0 in veg and 1.2-1.4 in flower that's great but the bigger guardrail in flower is flower tops <78° and keep RH in the 40's or 50's.
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I completely agree, for the vast majority of growers, VPD isn't all that concerning. For me tho, because I'm in raised beds, what I put in my soil.... I can't get out unless it's through the plants. Lol, can you imagine trying to flush a 4'x8'x22" fabric bed.... yikes!!!!
 
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