The Role of Humidity in Cannabis Cultivation

The role of humidity in cannabis cultivation

In an indoor cultivation environment, proper humidity control is vital for a healthy, high-quality crop. Humidity affects a plant’s growth, nutrient uptake and disease risk.

Maintaining a stable and optimal relative humidity for a cannabis crop is a key part of the cultivation process. Achieving this requires a comprehensive understanding of how humidity impacts plants throughout their life cycle.

Relative Humidity

Humidity is one of the most important and challenging aspects of cannabis cultivation, but many growers don’t have a thorough understanding of how to control humidity levels. This can result in poor plant health and a decreased harvest.

It can also lead to nutrient deficiencies, as the plants’ ability to draw water from the soil is reduced by a smaller-than-normal gradient between the plant and the atmosphere. This decrease in transpiration efficiency also reduces the amount of available carbon the plant can absorb, which slows growth and diminishes yield.

Keeping relative humidity at the correct level throughout the life cycle of a cannabis plant is critical for healthy, high-quality crops. The ideal RH is 55%-65% in the air and varies with different stages of plant growth (seedling/clones, vegetation, early flowering and late flower).

Young cannabis plants thrive in higher humidity than mature plants, so they require a higher RH during seedling and clone stages. This is because the clones and seeds are still growing their roots and they need to be able to draw water from the soil to develop their root systems.

The humidity in the air should be gradually reduced during late flower, as this encourages leaf and bud development without risking root and stem rot. This is an essential step for maintaining leaf and bud quality, as well as improving harvest yields and enhancing the product’s flavor and appearance.

When a grower underestimates their dehumidification needs, they put their facility at risk of limiting transpiration and nutrient uptake, leading to lower yields or severe crop damage from mildew and mold. The presence of these fungi and pests can also negatively affect the overall production of secondary metabolites, which is an essential part of cannabis growth.

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The best way to control humidity is to monitor the level using a hygrometer. This can be done with an inexpensive hygrometer that measures RH fairly accurately, or a more expensive psychrometer that can provide more accurate readings.


Humidity is a key metric to understand for cannabis cultivation. It is essential for maintaining proper growth and development, as well as for delivering high-quality output.

Transpiration is a natural process that occurs in plants when the water they absorb evaporates as water vapor into the air. The rate of transpiration is controlled by many factors, including temperature and humidity.

Temperature: Higher temperatures cause the stomata (openings on plant leaves where water is released to the atmosphere) in cannabis plants to open, whereas cooler temperatures cause them to close. Stomata are also controlled by the amount of light exposure the plant receives.

Wind & air movement: The faster the wind moves, the more vapor will be moved away from the leaf, which can result in an increase in transpiration. A good ventilation system can help to keep a consistent level of transpiration in the grow room.

Trichomes: Tiny hair-like structures on a cannabis plant’s leaves act as a barrier to water loss. They also help to hold humidity at the surface of the leaf, preventing the evaporation of excess water.

VPD: Vapor pressure deficit is a more accurate metric than relative humidity for measuring the water vapor in a growing space. It also helps determine if a particular crop is at risk of developing mold and other fungal issues, which can affect the quality and shelf life of the final product.

Lowering the VPD during cloning or transplant shock can alleviate plant stress, reducing moisture loss and ensuring a more healthy uptake of water and nutrients in the soil. Conversely, if the VPD is too high during the early stages of vegetation, excessive water loss may occur, which can lead to yellowing or burnt tips.

A vapor pressure deficit of 0.3 kPa is often recommended during cloning and transplant shock. It encourages the plants to develop a good root system and prevents excessive moisture loss. As the plants reach late vegetative and flowering phases, a VPD of roughly 0.8 kPa to 1.2 kPa is more appropriate. This will maintain a good rate of uptake and minimize the risk of nutrient burn that can lead to mold.

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Humidity is one of the most overlooked aspects of cannabis cultivation, but it plays a vital role in how your plants grow and their resilience to mold/mildew. It also affects how much water your plants need to drink and the nutrients they absorb.

In an ideal environment, your grow room will have a relative humidity (RH) that is between 55% and 65%. This is where a thermo-hygrometer can help you monitor your climate.

As plants grow they transpire (or draw in) the water they need from the air, which is absorbed by their leaves and transported through the plant. It is important to have a steady, even flow of moisture so your plants can perform at their best.

When the humidity is low, plants will take less water from their roots and they will not have the opportunity to take up nutrients through their leaves as quickly. This can lead to issues such as nutrient lockout or nutrient starvation which can result in poor growth and lower yields.

This is the reason why it’s so important to control the humidity in your grow space. The right amount of moisture in your grow area can boost your cannabis production by promoting optimal plant growth and secondary metabolite production, boosting the quality of the buds you harvest and reducing pests like fungus gnats and spider mites that thrive in a dry, humid environment.

The right humidity also keeps your buds hydrated when they’re harvested and prevents them from developing bud rot, or botrytis, which can cause a plant to wilt, or die, during flowering and can be devastating for your crop and business.

In a recent Cannabis Business Times (CBT) study, we found that nearly half of cultivators felt that their room humidity levels were either very concerning or concerning. In fact, many cultivators were unsure about their practices and were not in agreement on what their optimal room humidity level was for the different stages of growth.

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Temperature is a key factor in cannabis cultivation, especially when you are growing flowering plants. If you have a good set of temperature and humidity controls, your cannabis harvests will be healthy and potent.

When temperatures are too hot, plants can suffer from a number of problems, including root rot, powdery mildew, and nutrient burning. They will also grow more slowly and yield less.

However, if you can keep the temperature in your grow room within the ideal range of 68-77degF (20-25degC), you will see the best results. Straying just a little outside of these temperature parameters won’t hurt your plant, but you should avoid freezing temps because they can shock the roots of your cannabis plants and kill them.

Another key aspect of the temperature in your grow room is how it changes during the day and night. A plant needs a stable temperature at all times to maximize its potential for photosynthesis and growth.

The optimal vegetative temperature range is 76 to 78degF (24-26degC). Humidity levels should be low, between 40 and 70 percent.

During the flowering phase, temperature and humidity need to be kept low as well because fungi can thrive in these conditions. If the buds are exposed to too much heat during this time, they will burn away some of the terpenes and cannabinoids in your cannabis flowers.

To keep temperatures at the right level, use oscillating fans to increase airflow. This will help your cannabis flowers to dry out faster.

A good hygrometer will give you the exact RH levels in your grow room. You can also control the humidity with a mist nozzle attached to a fan.

When the weather is humid, your cannabis plants will need to take in more water than they lose. This means that you should water more frequently and more thoroughly than usual.

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