Humidity is too low!

First time grower so be gentle, what is the best way to generate more humidity in my plant room? Already have humidifier in the room, but it’s only staying around 40%. Help! Thanks y’allUploading…


I’m a gentle fellow, a few factors I suppose…most importantly, are you pulling to much air to fast out of your area? Negative pressure is great and all, but if your walls are caving inward, I’d start there :smiley: Good luck!

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What phase of growth are you in? Although rather low for vegging 40% isnt too bad. Its great if you are flowering. Do you have any pictures of your plants?


Still in very early veg. 4 weeks 4 days since germination

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Right on. Are the plants showing signs of not liking the low humidity?


Do some research on Vapor Pressure Deficit. This will tell you what your RH should be according to temperature. I keep my room around 60%-70% RH and temps around 80-85F. The links below explains it well.

To bring your RH up you will need a humidifier or fog maker. I went through 5 humidifier in two years (spending way to much money on each humidifier) before finding the House of Hydro. You can make a humidifier with simple parts they sell. It is simple to make and easy to replace parts. It also works better then any humidifier I have bought at Home Depot or Amazon.

Here is a youtube link on how to make a humidifier with the House of Hydro parts.

I made mine similar to the one above but single disc and with a 5 gallon bucket. 5 gallon reservoir needs refilled twice a week when it is -20F outside and dry as a bone.



I don’t think so, they are growing nicely and seem happy, I will try to upload a few pics

The ratio of plant size to room size is one of the biggest factors with humidity closely followed by the amount of ventilation. This is where you should look when wanting to change your humidity.

I don’t worry about low humidity too much. I often find my humidity is low during early veg and it is one of the signs to me that it is time to switch to flower when daytime humidity rises above nighttime humidity because they have reached the right size for their space and won’t end up too big.

If they are still small then you could reduce the amount of air you are exchanging. This would let them build up the humidity in the room. Watch your temperatures though, if it gets too hot turn off your light for a bit and it will get cooler and more humid. Your plants will like that and they won’t notice an hour in the dark.

If they seem happy they probably are. The humidity will rise as they get bigger.


Right on!! Thank you!

My plants were happy before increasing the RH. But having correct VPD has increased yield, bud set, resin production and made my plants happier.

I grew for a while before worrying about VPD or humidity. I always try to improve one thing every grow. Two grows back RH and VPD was what I improved. My plants are definitely happier.

My tip is to start researching harvest and cure. I ruined a lot of grows before I mastered the cure. Nothing worse then putting 4 months of hard work toward harsh and flavorless bud.




IMO 40% is fine, it’s actually perfect for flowering. I’ve grown in less than 40% for years w/ no problems at all. 30’s is fine and reduces the chance of mold or PM to zero.


Agree! Consider yourself lucky to have 40% humidity for flowering. For veg, I try to boost the humidity as well. I keep seedlings under a dome until they don’t fit anymore.

Do what you can, but it’s not the end of the world either. Most inline fans pull way too much air through the tent for humidifiers to be effective.