You need to keep you humidity quit high to get the most out of your plants.
Short answer is
VPD theory doesn't take into account essential oil production in plants. So, though it may be true plants can produce more leaf growth and overall biomass with high humidity, essential oil production typically suffers as a result.
For most plants that produce essential oils, they are produced as a means of slowing transpiration and quelling pest pressures in arid regions. This is why some of the most productive food growing regions of the planet are irrigated deserts.
Rainforests produce plants and trees with huge leaves.
Irrigated deserts produce food, fiber and medicinal herbs.
If anything, high humidity in veg with progressively lower % until bottoming out at the end bloom. Below 40% after 4 weeks in to bloom in my opinion or you're just asking for botrytis or other bud rots IMO.
All4freedumb- ask for knowlege, and it will freakin' rain textbooks around here! I find it interesting that Woodsman's preference for keeping RH high throughout the flowering phase still gets him good results, even while others drop their RH drastically through flower. I wouldn't bet against his results, I've seen the pics.
In general, higher RH in veg, then steadily decreasing RH through flower is the consensus. I prefer dropping RH slowly to allow the plants to adapt to it. I personally think making any large, sudden changes in their environment is a stress and so avoiding such big swings is generally better.
Another point to consider is WHY humidity matters; it directly affects how much water- and therefore nutrients- a plant can take up. Lower humidity can lead to nute burn because the plant is transpiring too much water, this also certainly stresses them too. One response to low humidity is to close the stomata under the leaves. This leads to an inability to take up CO2, rendering CO2 augmentation effectively useless. So don't go too low.
High humidity comes with its own pitfalls; here, the plant is taking up less water, and if RH is too high, it will be unable to bring up adequate supplies. You'll see this especially in 'non-mobile' nutrients like calcium. For higher RH, you want higher EC so the plant has access to enough nutes.
Clearly, a balance is called for, and that's where the above VPD chart comes in. For veg, I recommend about 75-78 degrees and 70% RH. For early flower, go up to 80 degrees and 75% while you're pushing CO2, and then dial back the RH by 5 points a week after week 4. Remember also to lower your nutes strength at the same time, to avoid nute burn issues.
Now this is ALL just what I needed.. those charts are exactly what I was looking for. I want you all to know how much I appreciate all of your guys shared knowledge.
I realize I have been completely out of proper ranges by either scales or opinions. I have sat between 40-50% in Veg. With that increase needed, I'm assuming swamp coolers would be my best choice? I'm also going to look into a twin set of big dawg dehumidifiers, one for each room, so I can keep everything where it should be.. Question, what about night time humidity? Whats the optimum goal for nights?
Ttstykk, you wrote about lowering my nute strength as well as my humidity. Was that from week 4 on to start tapering my nute strength with those 5 humidity points? I'm used to a slight increase in my nutes until week 6 normally, thats why I'm asking..
Deacon, thanks man, knowing your running the 100 pints now and wanting to step it up tells me to do the sane.. 160pint big dawg in each room.?
Woods,, your the one that has been slapping this chart and knowledge down on this humidity for some time now, I was hoping you'd post this.. I've see your pics too, AMAZING.. that's all I can say.. Thanks for sharing and I definitely need to look into running humidity all the way throughout, maybe a side by side? I got an extra epi and chiller... Just need a top off..
UCMENOW, Thanks for coming thru on this.. Your insight on this is where my mind has always settled.. I've always had a hard time with high humidity levels, although I always wanted them in my veg and have. Once I started running my UCs I dropped control of my humidity while vegging and still saw better growth using the UC without touching humidity control then post UC and high humidity... Now I been thinking, what if I brought that steam back but to my UC. I'll say this, just in two days of a 15% increase only hitting 55% at high I am seeing a huge step up in the girls overall health.. Co2 goes back in tomorrow.. I can't wait to see then.. I like the tapering down. What do you do with your co2 levels while hitting with higher humidity?
Thanks again guys.... A4FD...