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  • Writer's pictureAlexis Mellons

The Importance of Humidity in the Cannabis Growing Process

Growing cannabis is a delicate and intricate process that requires a keen understanding of various environmental factors. Among these, humidity plays a crucial role in the health and productivity of cannabis plants. In this blog, we will explore why humidity is important, how it affects cannabis plants, what the ideal humidity conditions are, how to maintain optimal humidity, and the negative effects of poor humidity control.

humidity in cannabis grows
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Why Humidity is Important to Growing

Humidity, the amount of water vapor present in the air, is a vital component in the growing environment of cannabis. It directly influences the plant's ability to absorb nutrients and water, affects the rate of transpiration, and impacts the overall growth and health of the plant. Proper humidity levels ensure that plants can perform their physiological processes efficiently, leading to robust growth and higher yields.

How Humidity Affects Cannabis Plants

Transpiration and Nutrient Uptake

Humidity influences the process of transpiration, where water is absorbed by the roots and released through the leaves. In an environment with optimal humidity, transpiration occurs at a steady rate, facilitating the uptake of essential nutrients from the soil. However, if humidity is too low, transpiration rates can become excessively high, leading to nutrient deficiencies and stunted growth.

Growth Stages and Humidity Needs

Cannabis plants have varying humidity requirements at different stages of their growth. Seedlings and clones thrive in higher humidity levels (65-70%) because their root systems are not fully developed, and they rely more on their leaves for moisture intake. During the vegetative stage, a slightly lower humidity (40-60%) is beneficial as the root system becomes more established. Finally, in the flowering stage, lower humidity levels (40-50%) help to prevent mold and mildew, which can devastate buds.

Stomatal Function

Stomata are small openings on the leaves that regulate gas exchange and water vapor release. Humidity levels affect the opening and closing of these stomata. In optimal humidity, stomata function efficiently, allowing for proper respiration and photosynthesis. In contrast, high humidity can cause stomata to remain closed, reducing CO2 intake and impacting photosynthesis.

ideal humidity in cannabis

Ideal Humidity Conditions in a Grow

Cannabis plants have specific humidity requirements at different stages of their growth cycle. Understanding why each stage requires certain humidity levels is crucial for optimizing plant health, maximizing yields, and ensuring high-quality buds. Let’s delve into the ideal humidity conditions for each stage of cannabis growth and explain why these levels are necessary.

Seedling Stage (65-70% RH)

Why High Humidity is Needed

Seedlings and clones have underdeveloped root systems and rely heavily on their leaves to absorb moisture from the air. High humidity levels in the range of 65-70% relative humidity (RH) create an environment where water loss through transpiration is minimized. This is crucial because:

Moisture Absorption: Young plants can absorb moisture directly through their leaves, compensating for the limited uptake from their immature roots.

Stress Reduction: High humidity reduces the stress on seedlings and clones, allowing them to establish their root systems more effectively.


Enhanced Growth: High humidity promotes vigorous growth during this critical early stage.

Disease Prevention: The controlled environment reduces the likelihood of diseases that can affect weak and vulnerable seedlings.

Vegetative Stage (40-60% RH)

Why Moderate Humidity is Needed

During the vegetative stage, cannabis plants develop a robust root system and large foliage. The ideal humidity range for this stage is between 40-60% RH. This moderate humidity level is beneficial because:

Optimal Transpiration: Plants have a well-developed root system by this stage and can efficiently take up water and nutrients. Moderate humidity supports optimal transpiration rates, which helps in nutrient uptake and photosynthesis.

Disease Control: Maintaining humidity below 60% reduces the risk of mold and mildew, which thrive in overly moist conditions.


Healthy Growth: Proper humidity supports the vigorous vegetative growth necessary for strong stems and leaves.

Pest Prevention: Lower humidity levels deter pests that prefer more humid conditions.

Flowering Stage (40-50% RH)

Why Lower Humidity is Needed

The flowering stage is crucial for bud development, and maintaining a lower humidity level of 40-50% RH is essential. Here’s why:

Bud Density: Lower humidity prevents the development of airy buds, promoting the growth of dense, resinous flowers.

Mold and Mildew Prevention: Flowers are particularly susceptible to mold and mildew, especially bud rot, in humid conditions. Lower humidity minimizes this risk.


High-Quality Buds: Ensuring optimal humidity during flowering results in high-quality, potent buds.

Increased Resin Production: Lower humidity can encourage the production of trichomes, the resinous glands that contain cannabinoids and terpenes.

Late Flowering Stage (30-40% RH)

Why Very Low Humidity is Needed

In the late flowering stage, reducing humidity to 30-40% RH becomes even more critical. This low humidity level helps in the final maturation of the buds. 

Preventing Mold: As buds become denser and heavier, they are more susceptible to mold. Very low humidity reduces this risk significantly.

Enhancing Potency: Lower humidity can stress the plants slightly in a beneficial way, potentially increasing resin and trichome production as a protective response.


Maximum Potency: The stress from lower humidity can lead to increased cannabinoid and terpene concentration, enhancing the potency and flavor profile of the buds.

Efficient Drying: Preparing plants for harvest under lower humidity conditions helps in the drying process, reducing the risk of mold during curing.

Each stage of cannabis growth requires specific humidity levels to support optimal development and health of the plants. By maintaining the ideal humidity conditions for seedlings, vegetative growth, and flowering, growers can ensure robust plant growth, prevent diseases and pests, and produce high-quality, potent cannabis. Understanding and controlling humidity is a fundamental aspect of successful cannabis cultivation.

maintaining optimal humidity

How to Maintain Optimal Humidity Conditions Inside a Grow

Use of Humidifiers and Dehumidifiers

Humidifiers can add moisture to the air when humidity levels are too low, while dehumidifiers can remove excess moisture when levels are too high. These devices should be used in conjunction with humidity sensors to maintain the desired range.

Proper Ventilation

Good airflow and ventilation help to regulate humidity levels. Installing fans and ventilation systems ensures that air circulates properly, preventing pockets of high humidity and reducing the risk of mold and mildew.

Environmental Controls

Advanced environmental control systems can monitor and adjust humidity levels automatically. These systems can be integrated with other climate controls, such as temperature and CO2 levels, to create an optimal growing environment.

Watering Practices

Overwatering can lead to high humidity levels and root problems. Employing proper watering techniques, such as allowing the soil to dry out between watering sessions, can help maintain balanced humidity.

Negative Effects of Poor Humidity Control

Maintaining the right humidity levels is crucial for the health and productivity of cannabis plants. Poor humidity control can lead to several negative consequences, each impacting the plant's growth, health, and overall yield. Let’s explore these effects in detail.

Mold and Mildew

Bud Rot (Botrytis Cinerea)

One of the most devastating effects of high humidity, especially during the flowering stage, is the development of mold and mildew, with bud rot being a significant concern. Bud rot, caused by the fungus Botrytis cinerea, thrives in humid conditions and can quickly destroy the dense flowers of cannabis plants. Once infected, buds turn brown and mushy, and the rot spreads rapidly, often leading to the loss of entire crops.

Powdery Mildew

Powdery mildew is another common fungal issue in high humidity environments. This fungus appears as white, powdery spots on leaves and stems, hindering the plant’s ability to photosynthesize. If left untreated, it can severely impact the plant's health and reduce the overall yield.

Nutrient Deficiencies


In conditions of low humidity, cannabis plants experience high rates of transpiration. This rapid water loss forces the plant to absorb more water from the soil to compensate. While this might seem beneficial, it can lead to an imbalance as the roots take up more water than they can process nutrients. Consequently, essential nutrients like potassium, magnesium, and calcium may not be absorbed efficiently, leading to deficiencies.

Nutrient Lockout

Additionally, when humidity is too low, plants may also suffer from nutrient lockout, where the pH of the soil becomes unbalanced, making it difficult for plants to absorb nutrients even if they are present in the soil. Symptoms of nutrient deficiencies include yellowing leaves, brown spots, and overall stunted growth.

Pest Infestation

Spider Mites

Low humidity levels create a conducive environment for pests like spider mites. These tiny pests thrive in dry conditions and can quickly infest cannabis plants. They feed on the plant’s sap, causing leaves to turn yellow and stippled, eventually leading to leaf drop and reduced plant vigor. Spider mites reproduce rapidly, and an infestation can spread quickly if not controlled.

Fungus Gnats

Conversely, high humidity can attract pests like fungus gnats. These pests lay their eggs in moist soil, and the larvae feed on organic matter and root hairs, causing damage to the root system. This can lead to poor nutrient uptake and weakened plants, making them more susceptible to other stresses and diseases.

Stunted Growth and Lower Yields

Physiological Stress

Incorrect humidity levels place significant stress on cannabis plants. When the humidity is too high, the plants may close their stomata to prevent excessive water loss, reducing the intake of CO2 and impacting photosynthesis. This physiological stress can lead to stunted growth and lower yields as the plant’s energy is diverted towards dealing with stress rather than growth and bud production.

Reduced Bud Quality

Poor humidity control during the flowering stage not only reduces the quantity of the yield but also affects the quality. High humidity can result in airy, loose buds instead of dense, resinous flowers. This directly impacts the potency and marketability of the final product.

effects of poor humidity

Additional Consequences

Root Problems

Excessive humidity, particularly at the root zone, can lead to root rot, a condition caused by pathogens like Pythium. Root rot results in brown, mushy roots that are unable to take up water and nutrients effectively. This condition is often fatal if not addressed promptly.

Electrical and Equipment Issues

High humidity can also affect the grow room environment by causing condensation on electrical equipment, leading to potential hazards such as short circuits or malfunctions of critical systems like lights and fans. This not only poses a risk to plant health but also to the safety of the growing operation.

Proper humidity control is essential to avoid these negative effects and ensure the healthy growth of cannabis plants. By understanding the consequences of poor humidity management, growers can take proactive measures to maintain optimal conditions, ensuring robust plant health, high yields, and superior quality cannabis.






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