So, I’m trying to dial this vpd thing down. I’ve learned that to high of a VPD can cause calcium deficiency, along with nutrient uptake issues, but to get the proper VPD at 78 degrees, humidity has to be 65%. Is that going to possibly cause bud rot? Plant is almost 5 weeks in, and seeing some of the described issues, so added a humidifier to hit that VPD number on the chart.
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I’m not sure I think it’s a little high but maybe with sufficient airflow you should be good?
Maybe lower it to like 55/60%
I remember reading on here that you shouldn’t go crazy chasing the perfect vpd
But this is my opinion, now I’ll leave it to the real experts here
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Ive spent alot of money chasing vpd and quit. In flower i try to keep my temps between 75 and 78 and my humidity between 50% and 55%
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Yeah, my humidity was 45 and temp 77. The humidifier on low has it 60% and 78 degrees for a VPD of 1.31. Closer to the target on the chart, but still a little high. Shooting for 1.15.
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A VPD of 1.3 is what I aim for. I wouldn’t change a thing lol. Plants look great!
You are right tho, VPD can cause all sorts of problems.
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@ChittyChittyBangin my bad man I forgot where I read it from and only remembered after reading your post,
I forgot and didn’t tag you
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Nice graph with metric thanks
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Easier than typing, sometimes.
Forgetting things without pictures.
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So did I. All the hype doesnt seem tomake a diff at all in our small grows. I know some swear you have to be exact but never have seen that need myself. Successful grows not ever checking.
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Mother Nature does not follow the charts, either.
I have a real hard time following the rules., also.
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If one uses a lung room with continuous ventilation through the tent, then trying to maintain a precise VPD will be very difficult. Not unless you bite the bullet and control the lung room. Not sure about the rest of you, but I don’t want to run my garage up to 75% humidity.
I just started some tiny seedlings in the 5x5 tent. I picked with a new AC Infinity humidifier last spring that was still in the box. This is a very impressive unit. It can be placed outside the tent, and has a remote humidity sensor that you can place in the tent. Also has a discharge tube that runs into the tent.
Since my basement is cool now, and the plants are so small I shut off the exhaust and intake fans. Set the humidifier to hold 70%, and this humidifier is holding set point great. The tent is only getting up to 71 degrees. So I ordered the AC Infinity smart outlet controller so the fans can be cycled by temperature or a time cycle.
All of this has me thinking about adding the AC Infinity CO2 injection kit to the mix, so that I can reduce ventilation fan run time even more.
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Exactly, it doesn’t need to be perfect, just within an acceptable range. Like 77 degrees at 55%, we all know that’s a good place to aim.
Some people measure using ec some measure for ppm, at the end of the day it’s the same thing.
Plus we see it here very often, they will tolerate way outside of that range!
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right!
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I just go by 10% lower from veg temp (ie. 70° 60% rH)
20% lower from flowering temp (ie. 70° 50% rH).
A simple glance at the monitor device and you’re good without charts.
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Did you notice that the numbers aren’t the same on both those charts? Let me add mine to your collection 
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VPD target numbers are Leaf VPD target numbers, while you are adjusting your “Room” or “Air” VPD numbers towards Leaf VPD target numbers. You need to know your leaf temperature &/or your leaf temperature offset to calculate leaf VPD (depending on the calculator, some ask for the leaf temp, some ask for offset), & you use the leaf temperature offset to select the correct VPD chart.
The constant for a VPD chart is the Leaf Temperature Offset. If that changes, so does the chart.
You can take a chart & run its numbers backwards through a VPD calculator to determine what the leaf temperature offset is for that chart.
The formula for Leaf Temperature Offset is:
Leaf Temperature - Air Temperature = Leaf Temperature Offset.
If the leaves are the same temperature as the air, then the Leaf VPD would would match the room VPD.
Hard to chase leaf VPD numbers, but good to know real leaf VPD numbers & what changes are actually doing to the leaf VPD. IR temp gun is good for checking leaf temps, bud temps, etc. Get one with efficacy around 93 (iirc, but feel free to look that up) or adjustable.
Read the statement above the chart, and that was the point.
I absolutely don’t care, but yes, I knew already. Simply stating that both charts mention air/room temp. Both have different numbers for say 70° all the way across. No mention of leaf temp offset on one. How’s some newb gonna differentiate? I just tossed in another chart for his collection. Have fun with your IR gun and plugging in your numbers to a calculator.
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Wasn’t really replying to you specifically, mainly posted for anyone who wants to know why.