High Humidity, questions

Hello, I’m just curious how to lower the Humidity in my grow tent. I’m currently about 3 weeks from harvest and with spring here we’ve had a lot of rain and these warm days are killing me. I have an AC and a dehumidifier running but I’m struggling to keep it under 50%. its only a 3x3 tent with 2 plants. I don’t know if I should get a bigger tent or maybe a 6 inch fan/filter instead of a 4inch? I’d put the dehumidifier in the tent but it puts off a little too much heat and didn’t even seem to help much when I tried. Idk any help would be appreciated I just really can’t afford to lose everything including my mind.

I have found that the only way I can adequately control humidity is to run a humidifier or dehumidifier outside my tent that is big enough to set the humidity in the room the tent is in, and then run a smaller one inside the tent for the extra 5-10% boost I usually need.

Doing it this way, I generally keep my basement (where all my tents live) at 50% RH using a whole house console-style humidifier and dehumidifier (depending on the season). Then, I put a dehumidifier or humidifier inside the tent (a small one).

If it’s more humidity I need, I use a cool-mist style humidifier in my tent. This usually will get my RH up to 55-60% with lights on and 65-70% with lights off with basement RH at 50%.

If it’s less humidity, I use a smaller dehumidifier inside the tent - that can get me down to 35-40% in late flower.

In conjunction with that, I put my exhaust and intake fans on recycling timers, and adjust how often and for how long the fans run to also manage temps and humidity. In the winter, I run my fans just one minute out of every five in order to help keep humidity and temps up in the tent.


I mean the room my tent is in sits around 35% while the tent itself is closer to 47%, at least until the lights shut off. But what size Dehumidifier would I need? I tried my 50pint and it was quite large and puts off too much heat to be efficient in such a small space. I also tried one of the mini ones and it did absolutely nothing. Is 50% RH in flower too high? considering you dry them closer to 60%… I just don’t think I can do anything for another 2 weeks and would only be able to get one of the 3 items I’m debating.

not to mention that may be a lot of power between the AC, 2 dehumidifiers, fans, lights and my computer all in one room.

Try and rig something to the dehumidifiers exhaust so you can pump that hot air outside the grow space

IMHO no. If you have good air flow (fans) it should be fine. Lower humidity does seem to increase resin-production from the plants (they are, after all, high mountain desert plants). The danger with RH 50+ percent is the possibility of getting grey mold or other fungi/mildews once you have fat, dense colas.

I like to keep my RH at the appropriate VPD level until the buds start stacking, then I start dropping it. I try to settle in around 35-40% the last few weeks of flower.

How big is the room your tent is in?


This is how I manage for temps and humidity in my grow space. Bought an inexpensive remote thermostat and that keeps the tent from doing too many air exchanges which affects humidity. That said, 50% isn’t bad if that’s all you can get. You will get more trichomes in a low RH environment but is it worth it?


I have my tent in my bedroom for lack of space but its about 10’x10’.
But are you saying too much air exchange can increase humidity or did i read that wrong? I mean either way I have 2x12" oscillating fans, one blowing across the tops and one on the floor, along with a filtered air intake but that’s the same size as the extraction fan so not sure if that’s a “problem”.

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Heat inside your tent will vacate moisture - i.e. lower humidity.

So, let’s say you have a 4x4 tent in a 10x10 room, and the humidity in the 10x10 room is 50%.

If you have your fans running 100% of the time in the tent and no other heat sources, the tent should normalize to the 10x10 room’s atmosphere - i.e. get the same RH and temp.

Now, if you turn your lights on, you will likely see higher temps but a lower humidity because of the increased temperature in the tent. Humidity is relative to temperature, so the exact same level of moisture in the air at 70F will feel like MORE moisture than it will at 80F.

So, if you want to raise the humidity inside your tent, one way to do it is to limit the cycling of air in said tent. I do this with a cycle timer that turns my fans on for 1 or 2 minutes, and then turns them off for, say, 6-8 minutes. I play with the cycle times at the beginning of each grow.

Things you have in your tent - like plants - can obviously increase humidity too, but if you are vacating all the air in the tent every minute, you are just exhausting that extra moisture.

I almost always run my fans 100% of the time in mid to late flower in an effort to keep RH down, and I rely on my dehumidifer to reduce the RH in my basement. You would want to do the same with your bedroom.

Yeah mine doesn’t work anything like that. My room is usually a nice 70F and around 30%RH, but my tent is generally 75 with the lights on and 45%rh if im lucky but with them off it drops to 66F and 50%Rh with the dehumidifier and the ACs dehumidifier on full. I don’t at all understand how its cooler in the tent than in the room or how the RH is 20% higher when I still need to water both plants.

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