Lights out humidity?

DanKiller

Well-Known Member
Best to stay under 60, my tent sometimes gets to 90+ RH lights out because I live in a very humid place, but my air flow is good and it's been like that all the time, I didn't see any bud rot or mold yet in my grows and I've done a lot of strains.
Very important to keep them separate
in my conditions cuz if they touch each other and create dense no air spots for more than a day it will begin to mold no doubt.
 

bigboerboel

Well-Known Member
If you can’t keep the lights-out RH below 60% you need to make sure the temps are low and you have airflow. I have decades of experience outdoors, and all my botrytis and PM damage has come when humidity coincides with warm weather calm winds. 60% is ok if temps stay below 65F and you have some fans going.
 

DanKiller

Well-Known Member
Air flow and space is key, mold loves dense tight air pockets tht get to 100% humid.
Also some strains are so dense and large they will mold no matter what RH you sustain as they have those pockets inside of them.
Its a delicate balance, on one side high temps and high rh makes everything grow better, but on the other end it's close to the red line in terms of mold and pm... Nothing is free in life haha
 

Star Dog

Well-Known Member
I don't ever see under 60% at best, around mid flower its nearer 70%+ and that's a constant battle, on occasion I've had to defoliate and I fkg hate taking away a plants source of power, but it's effective at lowering humidity.

The uk generally doesn't get humidity below 70% through the year, 85/100% being nearer the normal.
At this moment.
Screenshot_20240215_144816_Google.jpg
I've not seen rot in years (near a decade) I put that down to constant ventilation and air movement and also plant health, ime healthy plants don't get bud rot it's always the one the got burned, or the one with yellowing dead and dying leafs that get rott.

Why isn't rott more prevalent down inside the canopy where its cooler and more humid, there's growers here live in desert area's getting bud rot and high rh% certainly isn't a problem for them.

Ime high humidity alone doesn't cause bud rot.
 
Last edited:
Imo vpd is more for lights on, in order to get transpiration. For lights out you want to stave away bud rot so usually you need a somewhat lower rh than indicated by vpd charts.
OP: can you heat your growspace during lights out? Higher temps means lower rh.
I'm running my dehumidifier in the room at 40% keeping the canopy around 35/37% and about 74/77°.
 

DanKiller

Well-Known Member
That's very low but depending on what stage you are on in the grow.
If your in the last 3 weeks it's very good, if your vegging or just starting flower, everything will slow down.
 
That's very low but depending on what stage you are on in the grow.
If your in the last 3 weeks it's very good, if your vegging or just starting flower, everything will slow down.
Two weeks to go. First time with LEDs. Trying to figure out how things work. Little different than the hid's I used for 35 years.
 

Rocket Soul

Well-Known Member
I'm running my dehumidifier in the room at 40% keeping the canopy around 35/37% and about 74/77°.
Thats at night time, right? Then you should be well within margins. Make sure you have good airflow though cause leaf on leaf and dense cannopies create micro climates of more humidity
 
Top