While many cannabis growers identify sensitivity to the condition of the soil and the nutrients available for the plant, it’s environmental conditions that really matter. One of the environmental factors that affect the growth of cannabis is humidity.
Humidity can be defined as the amount of water vapor in the air. Generally, there are three types of humidity:
Specific humidity – The specific humidity of an area is the ratio of the amount of water vapor to dry air.
Absolute humidity – This is the actual amount of water vapor present in a given area.
Relative humidity – This is the ratio of the actual amount of water vapor present in an area compared to the speculated maximum amount of water vapor that the area can hold.
In cannabis growth, as with any other plant, the relative humidity is used. It is also worth noting that humidity and temperature are interrelated. The amount of water vapor that air in an area can hold increases with increasing temperature.
What Factors Affect Relative Humidity Control For Cannabis?
There are three basic factors that weigh heavily in determining the correct relative humidity when growing cannabis plants. They are region, genetics, and stages of growth. Although there are lessor and differing situations, these three have the greatest impact.
Cold regions have less moist air due to the temperature relation stated above. Growing cannabis in these areas means that the relative humidity must be increased to an optimum level. On the other hand, hot or tropical regions require less control of humidity as most cannabis plants are highly favored by relatively higher humidity.
A good number of cannabis varieties have been developed over the years. Some cannabis species are adapted to warmer and more humid areas while others are adapted to cold and less humid areas.
From germination to late flowering, the cannabis plants call for changes in the humidity levels. Since each stage comes with distinct metabolic reactions, the relative humidity needs also vary.
Why Is Humidity Important For Cannabis Plants?
To understand how humidity affects the growth of cannabis, let’s first understand the plant’s respiration process.
The sugars produced in the photosynthesis process must be converted to energy used to support plants’ growth. To convert the sugars, mainly glucose to energy and oxygen, later released to the environment, the cannabis plant must acquire carbon dioxide from the environment.
The carbon dioxide enters the plant via the stomata; tiny pores on the leaves. When this process occurs, some water from the plant’s water reservoir is lost to the environment. Relative humidity kicks in here as it dictates how much water the cannabis plant will lose to the environment.
Two scenarios can occur:
When the air is moist (high relative humidity)
The water concentration gradient is significantly reduced due to the higher amount of water vapor present in the air. This means that the cannabis plant will lose less water and hence remain in its best shape.
When the air is dry (low relative humidity)
The high water gradient created between the plant and the surrounding air causes high water loss. The marijuana plant will try to prevent this by closing the stomata, a process that compromises the vital respiration process.
In summary, relative humidity is vital to cannabis plants as it regulates the respiration process and its subsidiary activities such as water loss. For a cannabis plant to benefit fully from relative humidity, it must be maintained at an optimum level. It will also help if the humidity is also kept constant for an extended period.
Should Humidity Be Low Or High For Cannabis Plants?
Cannabis plants are grown in a relative humidity range of 70-40%. This is neither too high nor too low humidity. As discussed above, both extremes of relative humidity are potential causes of cannabis plant stagnation. It is also good to understand that high humidity may support the growth of mold that may affect the growth of your marijuana plants.
What Humidity Should I Have In My Grow Tent?
When you cultivate cannabis in a grow tent, conditions such as humidity and temperatures must be appropriately controlled. While by now we know that different growing stages of the cannabis plant require different levels of humidity, it would help if you kept the humidity in your grow tent relatively high for cannabis seedlings. Several factors affect the amount of humidity in your cannabis grow tent.
If the lights of your grow tent are always on, the temperature of the contained air is raised and hence the relative humidity. Poorly lit grow rooms have cold and dry air (low humidity).
If your grow tent is adequately ventilated, the relative humidity is reduced due to increased air circulation. Ventilation is required for mature cannabis plants that require low relative humidity.
Frequency of Watering
Watering cannabis plants in a grow tent increases the plant’s water intake through the roots. High uptake of water by the plant increases the water loss rate through the leaves, making the room more humid. The induced moist environment, in turn, regulates the respiration process keeping the marijuana plant healthy. Again, watering should be optimized to maintain the grow tent in the recommended level of humidity.
What Humidity Is Good For Cannabis Flowering?
The recommended relative humidity for a flowering cannabis plant is 40-50%. The moisture is reduced to this level mainly to prevent the growth of mold that is very vicious at this stage.
Did you know that mold infestation on one cannabis flower can ruin your entire harvest? Lowering the humidity in this stage is, therefore very crucial and should not be overlooked. The humidity can also be reduced below 40% when the cannabis is close to harvest. This, however, depends on how your cannabis plants respond to changes in humidity.
In conclusion, it can be said that humidity is an essential condition in the growth of cannabis plants. Always start with high relative humidity of about 70% for your cannabis seedlings and reduce the moisture gradually until the plant is ready for harvest, where the humidity should be around 40%.
Luckily, humidity levels in cannabis growing spaces can be detected easily using manual or automatic hygrometers. If your cannabis plants are in a grow tent, there is also an advantage of automatic reduction of humidity levels. Commercial size dehumidifiers and fans are used for this purpose.