Eddy GrowGurus Explain: How to control humidity in your grow room.

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humidity grow room cannabis
Photo by: @grasscityheadshop

Humidity level is very important when it comes to marijuana plant health, but really it’s true for any plant health from tomatoes to lettuce to weird and wonderful herbs. Plants need water in the air but too much can lead to terrible, terrible things like rot and mold and pest infestation. Since we have a community of thousands of growers, we we asked our GrowGurus to tell us how to control humidity in the grow room. How does humidity affect your plants and what is the best way to control humidity in your grow? 🤔 (And if you think you’ve got what it takes to be an Eddy GrowGuru, sign up here y’all!)

How to Control Humidity in Your Grow Room

Joe Snow snowtill89

First Figure Out the Humidity Level Your Plants Need

how to control humidity

I’d say the best way I know how to control humidity is simply with humidifiers and dehumidifiers hooked up to humidity control devices that turn it on or off once those machines get the humidity to a certain level. More importantly is figuring out what the ‘right’ humidity for your plants actually is, and this is commonly not known.

how to control humidity with a VPD chart

Growers should strive to follow what’s called a Vapor Pressure Deficit (VPD) chart (example above), which appropriates the humidity to the temperature in the room, which is important because temperature changes the molecular structure of the room, and in turn changes the amount of humidity needed! 😊


Control Humidity with a Mister or Fogger

cannabis humidity control

Best way in my opinion is with a humidifier (mister or fogger) that can be digitally set…consulting a #VPD index can always be great but it is really only for sealed rooms.


Start by Collecting the Right Data

how to control humidity

I agree, although in regards to VPD it is much more complex than just a heat and humidity chart. There are so many micro ecosystems in every grow that overall VPD is a great start or baseline. But it is near impossible to mitigate VPD on all parts of the plant at the same time.

I would say it’s most important overall to truly monitor your grow at crucial points regarding warm up and cool down along with average daytime temp/rH . Only then can you really begin to understand what is needed. For beginners I would suggest a simple hygrometer and a log. Gathering data on how the environment runs in all cycles is important before you can even pick the right gear to attempt control.


Focus on the Air Movement

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Great answers here on VPD not sure what to add.. just make sure that you have nice air movement through your canopy if you’re getting that RH up! And in veg: warm temps and high humidity 🤗


Remember to Focus on the Whole Room

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Balancing the whole room and not just the area around a portable dehumidifier is key. Custom solutions for different rooms = increased yield.


I prefer lower levels around 40% in flower for foliar feeding and lower risk of molds. Slightly higher for veg like around 50-60 and anywhere between 72-82 degrees with a good regiment of preventative treatments. Air movement is key. In my climate I actually find myself needing to add moisture at certain times of the year. And I add extra air movement and warmth in others.