Humidity: Finding the Sweet Spot for Your Grow Room

Humidity: Finding the Sweet Spot for Your Grow Room

Keeping the proper humidity in your grow space and finding the sweet spot that allows your plants to flourish into healthy yields is important.  Depending on the life stage your plant is in, you will be required to keep your humidity within a certain range to ensure your plants stay healthy.


Too much humidity and your plants will experience mold problems.  Bud mold is a huge catastrophe and when it occurs, it can lay waste to your entire crop in less than a week’s time.  Let's take a moment to examine the amount of humidity your plant needs in each stage of its life.




When your plant is just a seedling, it is going to require a slightly higher humidity.  A humidity level of 60% is an ideal scenario for seedlings to grow in.  Your seedling will have just started establishing their roots so they are going to have to rely on their leaves for the majority of their water consumption.  These higher humidity levels allow your seedlings to absorb added moisture from through their leaves.




Like seedlings, clones do not have a root system in place to feed with, so they must absorb the moisture from the air around them to survive.  Clones need high humidity, usually around 70%, to absorb enough water from the air to survive.  This is the reason you need to snip the tips off longer leaves when you are cloning.  This exposes the leaves veins to the open air and assists in moisture absorption.


Cloned plants should be kept under a dome and misted 2 times a day until they are rooted.  Cloning chambers work great at keeping your plant humid and allowing your light to effectively penetrate the canopy.




During the vegetative stage of your plant's growth, you should keep your humidity between 40% - 70%.  As your plants get larger, they are going to put off more humidity themselves.  This is going to require you to decrease your humidity as your plants form a larger canopy.  In most cases, a 5% decrease per week is optimal.  It is important to mention that genetics also play a major role in this equation.  You need to know the place of origin for your strain; this will allow you to replicate its preferred environment more effectively.


Plants that are in the vegetative state need air circulation.  Your plants should be vegging in a well ventilated grow space.  The more plants you have, the higher your humidity will become.  To adjust for this you may need to add additional fans to your grow room.




When your plant is flowering, it will produce dense thick flowers.  These crystal-coated flowers are unfortunately very good at retaining moisture, so you are going to have to watch out that your humidity doesn't go over 50%.  Depending on your genetics, you may notice your flower buds start to mold at around 60% humidity levels.  This is because the flowering stage of a plant is usually in the fall when humidity levels can be at their lowest.


Flowering plants need little humidity and if you live in an environment with high levels of moisture in the air, you are going to need to invest in a dehumidifier to keep your levels in check.  Bud mold stinks and it is a very effective killer of your precious yields, so be sure to monitor your humidity with a multi-function thermometer.


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  • David Hamilton
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