Humidity Levels needed for Cannabis

What Humidity levels at each Stage of Life

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Hi there and welcome (back) to Free the Tree!
In today’s article we’re going to cover the relative Humidity levels at each stage of life.
As you may know in nature the Humidity levels varie depending on the seasons, which all plants count on in order to thrive, Marijuana is no exception.
This means that at each stage of their lives you’re going to want to adapt the humidity levels within their environment for them to thrive

What Is Relative Humidity

Relative humidity is the ratio between the amount of moisture in the air and the greatest amount of moisture the air could hold at the same temperature.


In other words the hotter it is, the more water the air can hold. at that is because air holds different quantities of water at different temperatures.
When the temperatures in your grow room climb the humidity levels will climb with it and moisture starts to condense.

Where does the water go when temperatures drop?

Once the temperatures drop, at night time for example, it condenses onto the surface of plants and grow-room walls, just as dew condenses out side.

The greater the temperature variation, the greater the humidity variation will be, the more variation can increase stress to your plants.

Extra heat or ventilation at night can be necessary if the temperature variation exceeds 8/10°C (15°F)

Humidity Levels for Seedling and Sprouts

Seedlings and very young plants enjoy higher levels of humidity which allows them not to sweat too much, saving energy for the plant and enabling her to focus on root development.

Optimal Humidity

You’ll want to keep the humidity levels over 70/75% until the plant has grown her 1st or 2nd set of leaves. Once the main leaves have grown the plant can photosynthesis much better than using the cotyledon’s.
Growing 1st main leafs, seems to hold up

Humidity Level for Cuttings and Clones

For Cuttings humidity levels are one of the most important factor off success or failure.
We covered this subject in depth in our Cuttings guide.

When you’re cloning the plant you need to have the cuttings in an environment nearing the 100% humidity as long at the clone hasn’t rooted.
This is crucial, if the cutting starts to sweat your chances of success dramatically drop, your clone will most likely die.

cuttings in sealed cut of water for rooting

link here cuttings guide

Humidity Level during the Vegetative Stage

During the vegetative stage you’ll want to keep the humidity levels between 40% and 60%.

Higher humidity levels will

  • (May) increase chances of diseases
  • High humidity slows down evaporation rate
  • Stomata close
  • Slows growth

Lower humidity may/will

  • Lower chances of diseases
  • Increase plant sweating (water is evaporates easier)
  • Stomata’s open up
  • Growth increases
  • You’ll need to water your plants more often
Last week of the vegetation stage

It’s important to note that if you decide to go into the lower levels of humidity you’ll need to keep them well hydrated, or else this will be lived as a huge stress.


In any case you go for, as with the temperature you should aim for steady relative humidity levels.
If you decide to reduce or increase the humidity levels you should do so gradually

Humidity Level during the Flowering Stage

During the flowering stage you really don’t want to have high humidity levels or else you’ll increase a risks of mold developing.
Basically here you’ll want to stay in the 40%-50% humidity bracket.

8 BT buds flowering
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Humidity Level while drying your Weed

When you’re drying your weed you’ll need to have them in the dark and around 20/30% relative humidity.
You’ll want to keep them in that environment for about 10 days.

After this you will transfer the buds to the jar, where the curing can start. You can read about it in depth in the article dedicated to this, but basically you will want to open the jar a bit every day to keep the humidity levels around 50%

Critical and Fruit buds drying

Humidity Level to store your Marijuana Buds

Once you’re done drying and curing your buds, meaning that it’s ready to smoke (at least 2 weeks of curing after drying) you’ll want to store the buds in about 50% relative humidity.
Keeping them at that stage will avoid your buds to dry out and be totally flaky.


The other possibility is to place them in an air-free bag

Weed curing in air tight pot

Alright folks that’s it for this one, hopefully you found what you were looking! Don’t hesitate to message us if you need anything
Until next time, be safe and grow easy 😉

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