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Cultural Healing and Life

The Indoor Garden Environment - Part 3 - Humidity

JJ the Gardener

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The Indoor Garden Environment

~A Cultural Healing and Life Compilation and Writing.






Humidity is water vapor in the air.  The amount of this water vapor (humidity) in the air we measure is in terms of relative humidity.  Humidity has a  significant impact upon plants both positive and negative depending on the percentage.  Often I see people who prescribe negative aspects of the garden plants to other reasons when in fact humidity played a role in their issue more so than what they prescribed as the culprit of the problem.  Many times this is in part an aspect for stretch and rooting aspects..

When humidity is in the correct "relative humidity" levels for a plants specific development stage it is the equal of what a perfect outdoor day feels like to us air and breeze wise.  The kind of day where you think you could just stay out on the porch, in the yard, have a grill as the day just changes your plans for you. 

This is what we want to create for the plants and it is not as hard as you would think.  Learning about humidity and how to effectively manage it is a key aspect of ones evolution in indoor gardening as we learn how to use the tools of advanced gardening.  I warmly welcome you to the tool shed.


Humidity aspects

  • Plants Transpire
    • This is how plants cool themselves, like sweating.
      • They release water into the air
      • But when the air is already saturated (high humidity)
      • The plant shuts down at a certain point.
        • This is why in part high humidity is dangerous.
        • when the plant cannot transpire is can become the equivalent of being bloated and this makes it easier for plants to become infected by mold and mildew infections as their is much more water inside the plant it is easier to infect.
          • Especially plants that are stretched due to high nitrogen and low calcium uptake.
            • Weak cell walls + full of water in plant = easy for mold spore to drill into and infect internal plant water and infection.


  • Seedlings and cuttings are most sensitive.
    • Think spring light and humid environment.
    • Cuttings may use dome in traditional clone rooting
    • Cuttings in air cloners do not require a dome
    • Seedlings require a dome only until they come up.
      • Careful adjusting from climate of seed tray to next area.
    • Placing a clear film over top of early rooting plants raises the humidity at plant level.
    • Putting a dry light blocking material around plants will help with humidity in the plant area.
    • Humidity of 80% is ok
      • We do not want to put pressure on roots at this point.


  • Vegetative growth a higher humidity of 60 to 70 percent is healthy. 
    • Gradually increase as plants develop.
      • Pay attention to leaves and adjust humidity up or down accordingly.
        • Generally this is controlled by exhaust, and/or air conditioning.


  • Flower around 40 to 50% is healthy.
    • To high humidity in flower is inviting to mold and mildew spores.
    • Air conditioning & heat as applicable is sometimes used to manage humidity.
    • A dehumidifier is sometimes used to manage humidity in flower
    • Be aware of the electrical needs and amp requirements of a dehumidifier.



Humidity Summary

For most the next big thing is in some bottle or in an up and coming light.  In truth, utilizing humidity as a tool will enable you control the plant in ways many do not yet effectively appreciate.  We see that a plant will grow about anywhere and this aspect has caused many of us to misunderstand what a good grow environment actually is and thus our expectations are not aligned correctly and we often sell our selves short by simply not understanding humidity levels.

Now that we understand humidity and growing we can better use it to our advantage to help control stretch and root growth, create environment conditions like early morning, mid afternoon, later afternoon and night for each stage.  As with other indoor gardening tools control of humidity is as complex or as simple as one wants it to be. 

  • I recommend optimizing humidity for each plant development stage with root growth, transplant and transition stages.


Very good video regarding humidity.


How to control humidity indoors

Good information on greenhouse and urban farming.  Their youtube channel: https://www.youtube.com/user/BrightAgrotechLLC/videos


Too Hot


Too Cold


Fan control


Air Conditioning


Air Intake, Filter, Inline Fan, Ducting and Air Cooled Reflector Hoods



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