So although I’m growing indoors under a light, I am very much subject to atmospheric conditions because I’m in a shed. With that said, I’m able to add heat, add humidity, and (to a lesser degree) remove humidity. I am unable to cool the environment.
Low/high temp tomorrow is 67/89. Consulting a VPD chart, with a temp of 90 I’ve got to have 75% humidity just to be in a good VPD range. That sounds like a lot (I’m in very early flower), as the recommendations I’ve seen have said 40-60% rh for this stage. So is it more important to keep humidity in that 40-60 range, and just accept that my VPD is way high, or should I raise rh to get in that sweet VPD window, even though it will be too humid for early flower?
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Your VPD should be based off ideal humidity and then controlling the supporting temperature based on stage. Too many people think the opposite finding humidity for your temp. It’s all backwards. Control the humidity and support the ideal humidity with appropriate temps. This is why for most people VPD at home is a mouse chase. And most abandon vpd come flower for this reason. There is some sort of misconception, probably because it’s easier to control humidity than it is temps. However truly chasing this, cater to humidity first. High temps in flower lead to a loud (smelly) flower room due to evaporation of terpenes which begins to happen with temps between 70-72° for the more sensitive, and as temps rise the others follow suit.
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I wouldn’t go above 65% humidity at your stage with plenty on air flow..
Just my opinion.
More than that might invite mold to start.
Happy Growing
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Oof that’s terrible news. I really can’t effectively cool things down. I do have a portable ac in the shed, but it seems like it’s pretty ineffective at cooling the shed. I rigged something up that allows me to shoot the cool air directly into the tent, but previously someone told me it’s a bad idea because it puts the tent under positive pressure and co2 exchange is compromised.
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Yea that was my thought. It kinda puts me between a rock and a hard place. Can’t really lower the temps and it sounds like there are implications far beyond just a messed up VPD.
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morning Bfreezy…as home growers we will never be able to control our environments completely… VPD is like all other parameters …it is just something to know and how it affects your grow and how you might change it if needed… 
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Hey @Bfreezy, I chased VPD for a couple of grows when I first started growing. As you have found, it is a challenge.
I no longer even think about VPD. My grows do fine. 
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What are your thoughts on the ac set up? It would be nice to be able to keep things cool. I didn’t really understand what the guy was saying about positive pressure and the co2 exchange.
I have one exhaust fan running full blast, and I have another inline fan that I could use for exhaust or intake if that makes a difference. The shed is not sealed or insulated so there is probably plenty of fresh air coming in to the shed
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Yea, it sounds like heat is going to be my bigger problem. I’ve had 3 growing seasons prior to this, and things have always looked really good but smell has been minimal, and then when drying time comes everything really goes to shit
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Definitely can’t dry it in your shed at those high temps..
I mean you could but probably lose a ton of potency.
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That’s what’s happened with all my previous grows but I didn’t realize that was the cause until now. It’s frustrating because I’ve had pretty decent success and I think I’m pretty good at growing, but I’ve hit a ceiling that I can’t get past because of this gd shed.
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VPD is for those that have a fully controlled environment. Most of us home growers do not so we have to do the best we can. Just try your best to keep a steady temp/humidity level. Your plant will respond to consistency. Constant fluctuations will make the grow go south.
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For this I would just use the portable to cool/dehumidify the outside space (lung room) and have a good exhaust fan(s) in the tent to draw it in.
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(post deleted by author)
Deleted what I wrote because it said the same thing as BobbyDigital lol so I second the above comment. If you have the money for a climate controlled room then you can catch the elusive vpd, outside of that we are at nature’s mercy so to speak.
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That makes no sense to me. How could air pressure in a tent affect CO2 exchange?
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Co2 should be used in a sealed environment. So if the tent has positive pressure, the Co2 is being forced out of the tent. Co2 should not be used in our homes anyway. Just another way to seperate you from your money and possibly your life.
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Only problem is the ac can’t effectively cool the lung room. Just too much draft
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Don’t really know.
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No supplemental co2 being used
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