Managing Humidity in Cannabis Grows

Humidity management in a cannabis grow is a crucial aspect of ensuring healthy, high-quality crops. By controlling humidity levels within the grow environment, cultivators can mitigate various plant health issues, enhance growth rates, and maximize the plant’s production of essential cannabinoids, terpenes, and flavonoids. This article provides comprehensive information on managing humidity in cannabis grows.

Understanding Humidity in the Grow Environment

Humidity refers to the amount of water vapor present in the air. In a cannabis grow, humidity plays an integral role in the plant’s water and nutrient uptake processes. Through transpiration, cannabis plants release water into the atmosphere, creating a microclimate around the plant. This microclimate affects the rate of photosynthesis, the plant’s nutrient uptake, and its overall health and growth.

For cannabis plants, different stages of growth require different levels of relative humidity. For instance, during the seedling phase, a high humidity level of around 60-70% is ideal. As the plant grows and enters the vegetative stage, the ideal humidity level drops to around 40-70%. During the flowering stage, the humidity should be further reduced to 40-50%, and in the last two weeks of flowering, even lower levels around 30-40% can help prevent mold and bud rot.

Importance of Humidity Control in Cannabis Grows

Controlling the humidity within the grow environment is crucial for several reasons. High humidity can lead to the development of molds, mildew, and other fungal pathogens, which can destroy the plant. Overly dry conditions, on the other hand, can slow the plant’s growth, reduce yield, and make the plant more susceptible to pests and diseases.

The rate of transpiration is significantly influenced by humidity. In low humidity conditions, plants transpire more to cool down, leading to increased water and nutrient uptake. However, this can cause nutrient burn if not carefully managed. Conversely, in high humidity conditions, plants may close their stomata to reduce water loss, resulting in slower growth and potential nutrient deficiencies due to reduced transpiration.

Techniques for Managing Humidity in Cannabis Grows

There are several methods that cultivators can use to control the humidity levels in their grow environments:

Using a Dehumidifier or Humidifier

A dehumidifier removes excess moisture from the air, reducing the relative humidity, while a humidifier does the opposite, adding moisture to the air to increase humidity. These are two of the most direct and effective ways to control the humidity in your grow room. The use of these devices should be based on the current stage of the plant’s growth cycle and the ambient conditions in the grow room.

Proper Ventilation

Good ventilation is another essential technique for managing humidity. By ensuring a continuous flow of air, growers can prevent the build-up of moisture and promote a healthier growing environment. This can be achieved through the use of exhaust fans, oscillating fans, or more sophisticated HVAC systems.

Controlling the Grow Medium Moisture

Overwatering can significantly increase humidity levels as the water evaporates from the grow medium. Therefore, managing watering practices is another crucial aspect of humidity control. Depending on the grow medium, growers need to find a watering schedule that maintains optimal moisture levels without contributing to excess humidity.

Advanced Humidity Management: Vapor Pressure Deficit (VPD)

Vapor Pressure Deficit (VPD) is a more advanced method of managing grow room humidity that takes into account both the temperature and humidity. VPD measures the difference between the amount of moisture in the air and how much moisture the air can hold when it is saturated. When VPD is in the optimal range, cannabis plants can achieve peak photosynthesis and transpiration, leading to better nutrient uptake and ultimately, better yield.

A VPD chart, which correlates temperature with relative humidity, can help growers identify the optimal climate conditions for each stage of the plant’s life. A VPD-controlled grow room requires more sophisticated equipment, including precise temperature and humidity controls, but can lead to significantly improved results.


Managing humidity in cannabis grows is a complex process that requires a good understanding of the plant’s needs at various stages of growth. By employing techniques such as using a dehumidifier or humidifier, ensuring proper ventilation, controlling grow medium moisture, and utilizing advanced concepts like Vapor Pressure Deficit, growers can create an ideal environment for their plants to thrive.

Humidity management, along with other environmental control practices, contributes to the overall success of the cannabis grow operation. As such, the importance of these practices should not be overlooked by anyone interested in optimizing their cannabis cultivation process.