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There is no doubt that VPD is important; it has everything to do with transpiration, mineral movement, and basically ease of grow.
…So, you hear that and then refer to a chart that tells you the “good” zone and even more Intimidating, the “bad” zone, but is that chart without variables? What is “bad” when it comes to growing cannabis really?
Please hear me out…

VPD is giving new growers headaches and we aren’t helping anyone by stopping that conversation at “follow the charts.” –That’s like a math teacher telling his student to just follow the text book. If it were that easy we’d all be engineers. For you greenhouse growers, by all means, follow the chart if it works for your region, but us indoor growers need some info we can work with.
Again, hear me out…

Anyone who grows the DANK knows that these plants love it warm! The target leaf temp is between 80 and 85 degrees Fahrenheit during vegetative growth (that’s about 26 to 29 Celsius for all you non-Murricans out there). Anyone know what the chart says? You guessed it, 70-85% Humidity. That’s what we all run in our tents right? HA! That ain’t happening in my grow…again.
I’ll explain…

Most of us indoor, home growers are working with less than 100 sq ft. Now, let me tell you…I spent a week in Jamaica and it was constantly 80 degrees and 75% humidity during the end of November. I was in awe of ALL the plants. So much so, I tried to mimic that climate in a 4×4 tent. For a lot of growers, this is unachievable, but not for me; I have everything you need. So, I got the tent and the bedroom it is in right at 80 degrees and 70% RH. Wow! This felt NOTHING like Jamaica…it was unbearable and my plants didn’t tell me anything about preferring this for the 4 weeks of late veg that I kept it this way. I had to put an end to that because the outside temperature dropped into the 40’s (5-10 Celsius) and created some condensation issues on an exterior wall from the floor. My house was built in 1964 on a crawl space. This is when I put down the chart and went back to watching my plants, regulating transportation and  adjusting my feed & lights accordingly.

Conclusion…
I dropped the humidity down to 60% and used my handy dandy PULSE Monitor to get a good indication of how much my plants were transpiring and kept my leaf temps from rising above 82 degrees so that they weren’t drinking too fast.
A little TIP: if your plants are drinking too fast, you may notice some tip burn even if you’re not feeding heavily. Which is a good point because dialing in your grow means taking all variables and making them work symbiotically, it’s not a one size fits all and it’s not all about the perfect VPD.

The cover photo is my Dank Nugs entry of this one plant in week 5. She’s sitting in a 25gl pot with a 4×4 to herself.
Also attached are a 24 hour log on my PULSE (which may not be the right file type to upload) the vegetative VPD log, and here’s a link to the flowering chart no one talks about:
http://www.just4growers.com/media/23631/vpd_2degree.gif

The grow talk questions are, can ya’ll relate to my opinion on VPD for veg, and do you have something to teach me, please?

Sincerely, thank you to everyone who makes the DGC and the Dude Grows Show possible. I’m a Paying member because indeed you have effected my grow in a VERY positive way.
Keep growing and keep growing.
PEACE