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What’s the Best Humidity for Growing Cannabis?

Written by Taylor Christianson Nov 11 2021

The best humidity for growing cannabis can change a little depending on the strain as well as whether you’re growing cannabis indoors or growing cannabis outdoors.

What impacts relative humidity for cannabis plants?

When cultivating cannabis, three primary parameters must be considered when calculating the optimum relative seedling humidity: region, seed genetics, and growth stages. There are several more minor and more varying circumstances, but these three are the most significant.


Colder places have drier air because of their temperature-temperature correlation. Raise the relative humidity for cannabis plants to an ideal level in certain areas. Humidity management is less critical in hot or tropical locations since most cannabis plants prefer greater humidity levels.

Seed genetics

Many new strains of cannabis have been created throughout the years. Some cannabis species thrive in humid, warm climates, whereas others thrive in dry, cold environments.

Grow stages

Humidity adjustments are required during the cannabis plant’s life cycle. Different metabolic responses need varying relative humidity levels at each step.

How do temperature and humidity interact?

Humidity for growing cannabis is linked to temperature. Relative humidity (RH) is the proportion of water vapor partial pressure to the highest vapor pressure of constant temperature when discussing humidity for cannabis. Warm air contains more water vapor than cold air. Ventilate a grow chamber with fresh air as heated air holds more water vapor

For more information on the best humidity for growing cannabis indoors – check out our guide on the ideal temp and humidity for a grow tent.

Why is humidity important for cannabis?

The quantity of water your cannabis plants require vary based on the cannabis seedling humidity in your growth chamber during the various phases of development. During high humidity, cannabis plants utilize their leaves to get moisture from the air rather than from the roots, resulting in less water. Conversely, when the humidity for cannabis is low, the roots will draw in more water. You may effectively control plants’ nutrient intake by controlling humidity for flowering cannabis as it affects how much water they consume, and the water you feed them contains nutrients. There is more to managing cannabis flowering humidity than merely keeping it out of the air.

The thermometer and hygrometer in hand show the temperature and humidity next to the cannabis plant. The humidity indicator is indicated on the screen of the device in percentages.

Healthy, green plants thrive when the humidity level is just correct. It is challenging to regulate out-of-control crop growth while using DWC (Deep Water Culture) or Bubbleponics during the vegetative stage. When your plants are in the blooming stage, you should control the best humidity for cannabis plants in your grow environment. Controlling humidity will increase the amount of resin that your plants generate while protecting them from mold. Mold and bud rot might be a grower’s greatest nightmare for those big, thick main colas if the cannabis humidity is too high.

Humidity at different grow stages

When it comes to cannabis cultivation, we must clarify what we mean by cannabis humidity and temperature regulation. To keep cannabis plants healthy, splitting their existence into three phases makes sense, each of which requires distinct amounts of humidity and temperature adjustment. Don’t underestimate the value of ideal humidity for growing cannabis and temperature regulation! It’s a simple matter of ensuring that all parameters are inside a specified limit and as stable as feasible.

A hygrometer and thermometer, ideally a digital one with a memory function and can display the highest and lowest readings of the past, are the first things you should get. Please don’t bother with many hygrometers in your growth chamber since some of them aren’t the most accurate. As a result of our improved monitoring capabilities, we can now focus on the most critical aspect of the ideal humidity for cannabis and temperature control: achieving the desired humidity and temperature.

Seedling humidity 

  • Seedlings and cuts appreciate 65 to 70 percent humidity levels since their root systems have not yet developed.
  • During periods of high humidity, leaves can absorb water via their stomata.
  • Heat: 20-25 C° with the lights on, 4-5 C° less with the lights off

Cannabis veg humidity 

  • Every week humidity levels may be reduced by 5%. (acceptable range: 40-70 percent)
  • Higher water evaporation via leaves cools crops, allowing them to take in more water
  • 22-28 C° with the lights on, and 4-5 C° lower with the lights off

Humidity for flowering cannabis

  • Adjust moisture content to 40-50 percent (very critical) 
  • You could get away with 55 percent (anything above 60 percent is pretty terrible) 
  • It’s better to reduce temps in flowering slightly
  • Temperatures with lights on 20-26 C° (avoid excessive temperatures)

How to change humidity

Here’s how you can use heat and humidity to fix typical cannabis issues:

Lowering humidity 

Removing water from a dehumidifier is time-consuming in humid places. Once dehumidifiers amend humidity to a certain extent they will shut off automatically. After this happens, you should use manual means.

More air will flow through the growing area if you boost ventilation (either by installing a more powerful exhaust fan or improving your existing exhaust system). If you want to reduce the RH in the grow room, this technique is only effective if the air entering the room has a lower RH than the air already in the room.

Suppose you plan to use a high-powered exhaust fan to reduce cannabis grow humidity. In that case, you might also want to think about getting an atmospheric regulator with a cannabis veg humidity option to automatically change the fan speed to reach the desired humidity level for cannabis.

Increasing humidity 

Evaporative humidifiers are my favorite since they give moisture to the air and serve to moderate the temperature. Get a humidifier with a big storage container (which holds at least 6 gallons of water at a time). They generally need many refills each day for the 1.5-gallon tank “one-room” humidifiers.

If the relative humidity for cannabis seedlings is far too minimal and the warmth is too high, use a swamp cooler to chill the air while raising the relative humidity simultaneously.

A final word on cannabis humidity

As cannabis plants mature, the best humidity for flowering cannabis is a vital factor. You must keep your cannabis seedlings at a relative humidity of 70 percent until ready to be harvested. Once ready to harvest, the humidity level should drop to 40 percent. You may measure humidity levels for cannabis growing areas simply with hygrometers, which can be manual or automated. Humidity levels can be automatically lowered if automations are properly set up. Employ fans and dehumidifiers in larger spaces.

Taylor Christianson

Taylor is an indoor expert. Through their writing, they offer a masterclass on growing cannabis indoors, maintaining a productive growing environment, and guiding growers through all the stages of growth both indoors and outdoors. Combining multiple fields of expertise allows for Taylor to give in-depth insights into overall cannabis growing. About this Author

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