Environment, Climate & Stress
Humidity
Humidity is the amount of moisture (water vapor) present in the air around plants.
What Humidity Means in Cannabis Cultivation
In cannabis cultivation, humidity refers to the concentration of water vapor in the air within a grow environment. It plays a crucial role in plant health by influencing transpiration, nutrient uptake, growth rate, and disease risk.
How Humidity Is Measured in Grow Environments
Humidity is most commonly measured as relative humidity (RH), which expresses how much moisture the air is holding compared to the maximum it could hold at a given temperature. For example, 50% RH means the air holds half of the moisture it is capable of holding at that temperature.
Why Humidity Requirements Change Over the Plant Life Cycle
The importance of humidity in plant growth has been studied since early agricultural science, as growers observed that plants in overly dry or overly moist environments struggled. Cannabis plants have different humidity needs throughout their life cycle. Seedlings and clones prefer higher humidity to prevent moisture loss, while flowering plants require lower humidity to reduce the risk of mold.
How Humidity Affects Transpiration and Nutrient Uptake
In cannabis cultivation, humidity directly affects transpiration (the release of water vapor from leaves), which drives nutrient movement from roots to leaves. Low humidity increases transpiration and can stress plants, while high humidity slows transpiration and can lead to nutrient deficiencies and weak growth.
The Relationship Between Humidity, Temperature, and VPD
Humidity is closely linked with temperature, dew point, and VPD (vapor pressure deficit). Managing humidity without considering temperature can lead to condensation and disease, especially during lights-off periods.
Common Humidity Challenges and Control Methods
Common challenges include fluctuating humidity due to plant size, watering practices, and poor ventilation. Growers manage humidity using exhaust fans, dehumidifiers, humidifiers, and air circulation.
Related terms:
Relative Humidity, VPD, Dew Point, Transpiration, Ventilation, and Environmental Control.
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