I’m facing a bit of a dilemma and would love to get your thoughts.
I’ve always seen the advice: “Never run a humidifier during the flowering stage to prevent bud rot.”
However, I live in a hot climate, and my tent temperature is consistently between 25-30°C (77-86°F), and the ambient relative humidity some days is 70%, other days it drops as low as 50%.
The issue is that on days when the temperature is 30°C, the VPD chart for flowering says I should be aiming for an RH of 70-75% to stay in the ideal range. But on these hot and dry days, the only way I can possibly hit that target is by running my humidifier.
So, the question is, do I turn on the humidifier to reach the VPD, running the risk of mold, or do I keep the humidifier off, and let the plants deal with a less-than-ideal VPD on those hot, dry days?
Yes, I have a temp gun, and the leaf temperature is consistently 1-2°C below the air temp. I’ve been using a chart that also takes both parameters into account (vpdchart.com), but even so, there are days when I can’t get into the ideal range without the humidifier.
This makes me wonder about the trade-off. In your experience, what causes more stress to the plant during flower: A significant deviation from the ideal VPD (running too high/dry)? Or the potential risk of bud rot from raising the humidity to correct the VPD?
I’m trying to understand which is the lesser of two evils here.
In my experience a lot of that would have to do with the genetics you’re growing, how dense the flower structure is, how fast they stack etc.
Most typical 9-week hybrids that get dense, you should worry about that humidity in the second half of flowering… If your air movement is good however, you can ride that VPD line even if the humidity is up there. This is also assuming you’re under led, things change under hid.
Just my limited experience… If what you’re growing is more sativa and looser bud structure, it shouldn’t be much of a concern if your air movement is good.
Everybody’s environment is different. But where I’m at, I’ve had more issue with mold post-harvest than during the grow, unless the buds were bigger around than my fist… Then it is a definite concern during flowering.
I would avoid the mold zone even if that means non ideal vpd. This is based on rooms molding not bud rot, but 85f @ 75% would grow mold in 28 days, not good in my opinion
I have similar VPD problems to you in summer and I’ve found good air circulation above and below the canopy helps alot, also dont let buds touch each other or the tent walls.
