VPD questions

Could someone with knowledge in this area chime and let me know if its okay to grow via VPD chart in a perpetual flower room. My room is setup so I can keep whatever temps and humidity I need (also using co2), I would like to grow via the VPD chart (low 80's temps and ~75% humidity) but I am not sure if this is an issue in late flower. My room is perpetual and always have plants in the final weeks of flower. Anyone with experience with this have any input please?

thanks all

i use the vpd chart till week 5 or 6 after that i'm not trying to get any mold or bud rot so i go down to 50% humidity the rest of the way. I've alwasy done it like that sorry can't help you but imo i wouldn't risk high RH in late flower.

I wonder what is the highest RH can go with out mold problems?

I use VDP in veg only. I do 60% in flower all the way to harvest. Don't need any mold/rot issues like above.

The best weed I've ever seen is grown at 85/80 all throughout flower. I've always been skeptical, and never really went full retard. Didn't matter to me how good the weed was, I didn't want to run the same strain at the same humidity. This time I'm taking it 75-80% the whole way. It's about the last thing I can think of that I'm not doing for this strain..

Not advocating high humidity, just noting that I've seen it done very successfully for 10+ years with no mold problems growing large lanky sativas.

Great Question

You can still drop the RH down to 60 at the end of flower just make sure the ambient temps line up with the chart. I believe an RH of 60 would put you around 70 degrees F but just check the chart. Good luck

VPD is the closest model of how a plant "feels" humidity we use. It's a far better judge of what is going on than relative humidity. 50% or 85% humidity at different temperatures mean totally different amounts of water in the air and ability for the air to pick up more water. I can understand why you would feel safer running dryer near the end, but run a higher VPD, don't pick a % to shoot for regardless of temp.

Also be very careful about lights off time. As the room cools, you can get very close to the dew point if you're not dehumidifiingin some way.
When the lights are out, stomata close. So, basically the reason for keeping a healthy VPD doesn't matter.

Another note, VPD should be calculated based on leaf temperature and humidity of the air around the leafs. In a dense canopy, there will be a wide range.