the humidity in my room without a humidifier is around 20 to 32 %
I like what I read about having a higher humidity level
what I do not want is mold
so my questions are what is a good level to be at and should I put it on a timer and for how long on and off

I aim for 50-65% RH during veg. Keep a gentle breeze blowing throughout grow area and on plants 24/7… and mold will not be an issue.

As far as timer, whatever it takes to maintain the humidity.


You want higher humidity in veg, around 50-65 and in flower you want the RH 50 or lower. In late flower, a RH of 20-35 is gonna help bring out the trichomes :v:


big thanks on the info

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You don’t need a timer. The humidifier will have a humidistat built in and will keep things within range.
You didn’t say how big your growing space is, but depending on room size and the type of humidifier you get, you may wish to point an oscillating fan at it in order to circulate the moisture.
Also, here are my notes on humidity, kind of combined from what all the experts on here have shared:
Seedlings 70%
Vegetative: 40%-70% (I aim for 60%)
Flower Week 1-55%
Flower Weeks 2-5 50%
Flower Weeks 6-7 45%
Flower Weeks 8-9 40%
Final Weeks less than 40%


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Ive run a humidifier in Veg and will for preflower for current first grow and will continue to do so for every grow.

I have it set on a timer and let humidity fluctuate every 30mins

Thats what my Granny always said…:>)…

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the grow area is a 3x9 and it is a cool mist humidifier
the purpose of the timer I thought so it could turn off during lights out
and one 6" fan on at all times

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I have a 3x3 tent and ran my humidifier on a timer. I would run it for 45 minutes at lights on and 30 minutes at the 9 hour mark of my 18/6. I found that running my humidifier like this kept my humidity levels in the Goldilocks zone for my little world.

Here is the chart I use


@GreenJewels Thanks for posting that chart it is the best one I’ve seen! Merry Christmas and Happy New Year!

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Merry Christmas and Happy New! :v: I liked it best because it lists early veg, late veg/flower and late flower. Other charts I’ve seen just list flower. I have definitely noticed a nice difference in growth when I can keep my VPD in proper range. Happy growing and glad I could help :slightly_smiling_face:


That chart is great and I thank General Hydroponics for creating it, but I’ve found it to be annoyingly busy - plus the temperature values are in Celsius instead of Fahrenheit like we use in the United States.
So, I took it upon myself this morning to convert the values and make a new chart that is in Fahrenheit, only shows a sane temperature range (outside of which we would be killing our plants) and has humidity gradations of 5% instead of 2.5%, making it less busy.
I hope this proves of value to others:


@TommyBahama Thanks for doing all the work converting it to degrees F.


Shamelessly ripped you off, dude! Great chart and addresses the things that pissed me off on the other chart, lol. Printed one up and it’s gonna be hanging in about 2 minutes.


@TommyBahama thanks, that is much better. I printed mine off and have a paper copy and added F° conversation. We’re were you 3 months ago :joy::joy: This would have saved me time. I also made a little cheat sheet with only temps that apply to me and ideal rh range for each temp. Happy growing and thanks again :v:

great charts thank you

That’s a great chart! Temp and humidity is every bit as important as pH!

To high and it invites mold, to low and it’s hospitable to things like SPIDER MITES!

In which case (spider mites) I was successful in eradicating them using liquid ladybug and quarantine.

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@GreenCoat & @Bubblehead was wondering what humidifiers you both are using? Have InkBird controller in the waiting to be hooked up. Won’t work with my TaoTronics humidifier due to it having a push button turn on/off mode. I need something that as a permanent stay ON switch. Thanks