Mark D
 ·   · 104 posts
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VPD vapor pressure differential

Has anyone else dived into VPD on their tents/grow rooms? With the AC controls, setting up to control VPD in the tents is pretty interesting and easier I think.

I think if your using co2 in your grows this might be something you're aware of. 

If you are using VPD what methods are you using? Basically what methods are folk using in monitoring and controlling VPD.

Sometime asking is better than Google.

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    • I do and if I am not mistaken Stick was the first on to mention it on here but I looked into anyway. There is a lot of good info out there on it and a lot of things to consider. The VPD of the Room and the VPD of the leaf surface are important and yes they change if you have enhanced the atmosphere with C02. 

      This is a pretty good site for calculations and you can download their charts or find them someplace else.  

      https://www.dimluxlighting.com/knowledge/vapor-pressure-deficit-vpd-calculator/

      So here's what you do. 

      1) Buy a IR thermometer. I assume you have some kind of RH meter.

      2) Start taking the RH measurements and Leaf Surface temps at various areas in your grow room and write them down. 

      3) Compare what your numbers are compared to what the VPD chart says

      4) Give up sleep for a month or so worrying about how to make it perfect.

      5) Follow this simple chart for temps and RH and use the IR thermometer for cooking

      https://www.growweedeasy.com/humidity

      Seriously I do think environment is a huge factor but how beneficial is micromanagement to that point I really dont know  

       

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      • Cpw, having averaged the leaf temp and surrounds, room temp and have my offset and have a chart to look at.

        This all makes sense, but what happens at night? The humidity rockets and it drops 10 degrees(the light) now the vpd is way off. How does it all work after dark? I understand the dynamics that at night vpd isn't as important because respiratory changes, but how can you control the change so it isn't so dramatic on the plants. I think this is the droop you see before lights out, changes to respiration in anticipation of sunset. 

        As always it isn't critical just want to learn more about it. Never cared about this before and the girls did fine. But I think I can do better and this might be the ingredient that tames the environment and makes it friendlier to the plants. They say better controlled environment gives better results. Tell that to mother nature!😄

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        • I think the charts are all for lights out and, like RbtAsq said, (to the wind apparently because I cant find it) put your dehumidifier on a timer, I use these to try and keep the environment in tune and after I figured out the R/H and Temp swings during the year they work pretty good. 

          https://www.amazon.com/Inkbird-ITC-308-Temperature-Controller-Humidity/dp/B08HLRPGPJ

           

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          • This is above my pay grade..

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            Grow room setup
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