What percent humidity are you guys running into bud rot / mold

Looking for some numbers to ponder. My room is sensitive to the dehumidifier as far is heat goes. I’m running 1500ppm CO2 in the room. 45% its it 95 degrees, 50% its 90 degrees and 55% its 85 degrees. I’m at 55% right now and am wondering what you guys/gals think about that.

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FYI CO2 is a waste of time and money for the vast majority of growers. Higher temps and a ton of lighting is required for the supplemental CO2 to benefit the plants.

Re humidity, ideals levels by temperate are:


ton of lighting check
high temps check
Co2 equipment check
sealed room check

what does VPD stand for?


Vapour pressure deficit, its the relationship of temperature to humidity that plants thrive in, where maximum transpiration rate is achieved.


I found 70% to be the cut off for issues. 60% there’s risk, and 50% I would consider safe.
I was monitoring tent RH levels, and didn’t find wpm until it got above 60%. I increased air circulation, air exchange, and fired up the dehumidifier.


What age (how old from seedling or flowering) are your plants?

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I’m in the 5th week of flowering.

Oh, sorry @Covertgrower. That question was intended for the OP.

My thinking is along the lines of yours. I pretty much ignore the VPD chart and I try to run between humidity 50 - 65% for most of the grow and then fire up the dehumidifier and try to run 35 - 45% when the flowers start getting dense so as to prevent bud rot. I’ve never had any problems doing this.


agreed… i run my veg side at 55-60% solid and my flower room between 40-50 in the day… 40% in the lights out cycle…


my particular set up is a 10 plant system, like an assembly line. when all 5 stations get filled up, I will be harvesting 2 plants every 2-3 weeks roughly. when I flush the 2 plants in the final station, I will start germinating 2 more seeds and all the plants move to the next station when I harvest. So, basically there will be plants in all ages all the time in the room. they get plenty of air movement and right now I’m thinking with the dehumidifier set at 55%, the temps stay around 85-90 degrees. Seems reasonable to me but, I thought might as well ask and see what the rest of you have seen.

55% for veg is totally fine… Flower i would try to stay between 40-50%… 85-90 degrees however might give you some heat stress issues that can develope into several things so i would try to keep those temps down a bit if possible…

That’s where the Co2 comes into play. It’s my understanding the plants can take higher (no pun intended) temps. I have never seen what temps are considered higher. I haven’t had to deal with bud rot so far but, I saw pistils last Sunday on my OG Kush. I’m just trying to solve problems before they start.