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Humidity plays a major role in the cultivation of cannabis. A lack of treatment will reduce the overall quality and output, and risk disease outbreaks, such as bud rot (also known as gray mold or botrytis). Understanding how humidity is created and controlled, as well as how to best incorporate dehumidification, is essential for commercial and medical-grade cannabis growers.
How humidity builds up in greenhouse and indoor cultivation
There are several reasons humidity builds up in a grow room. The two leading factors are transpiration and temperature. Active, living plants transpire water vapor as part of their physiological activity. In a closed environment, this vapor rapidly builds up in the air and may quickly reach saturation. Relative humidity is a factor of both the amount of water vapor in the air and temperature. At lower temperatures, the air can hold less vapor. This drives the relative humidity up. Even a short drop in temperature can cause humidity spikes. When relative humidity reaches 100%, water begins to condense on cooler surfaces, such as railings, pipes or even the plants themselves.
Benefits of humidity control in cannabis grow rooms
By closing the growing space, growers can better control their climate. Keeping black screens or thermal screens deployed and using a dehumidifier to control humidity lets growers reach and maintain a comfortable VPD (vapor pressure deficit) level. This is true throughout the day, including overnight and during dusk and dawn when climate conditions change rapidly.
Maintaining an optimal VPD level ensures minimal humidity related problems, while also promoting an active climate which stimulates plant activity, leading to higher quality products and larger outputs of both dry weight flower and compounds. Optimal VPD levels for cannabis are around 0.8 kPa – 1.2 kPa, depending on cultivar and growth stage.
Maintaining correct VPD levels reduces condensation that may occur in the growing space. By eliminating the presence of free water, growers can eliminate the development of fungal pathogens such as botrytis and powdery mildew.
Another major benefit of a closed and controlled climate is uniformity. Keeping the same climate conditions throughout the entire growing space further ensures a problem-free grow. It also ensures a more consistent crop, both in terms of quality and quantity.
By consistently operating in a closed system, with the optimal climate conditions for the plants, growers ensure maximum plant health. The plants themselves grow stronger and less susceptible to diseases, while perils such as molds and pests are cut down drastically. This reduces the need for chemicals such as fungicides and pesticides, which are highly regulated in the cannabis industry.
How to best incorporate dehumidification in cannabis cultivation
To achieve the best results with humidity control, it’s important to understand that dehumidifiers have an operating capacity in terms of:
For these reasons, dehumidification must be tailored to the growing facility in order to reach satisfying results.
These are the main factors to consider when incorporating humidity control in a growing space:
The size of the growing space plays a major role in the success of humidity control. In order to achieve the best results, the airflow capacity of the dehumidifier, or dehumidifiers, must be sufficient for the space size.
If the room is too large, the dehumidifiers will fail to reach the entire space. This will lead to an uneven climate, including the formation of microclimates and local humidity spikes.
This is especially problematic when it comes to eliminating fungal pathogens. The presence of free water, even in a small area, is enough to cause the development of molds, after which the fungal spores will travel to the rest of the greenhouse.
The type of crop determines the rate of transpiration. If the rate of transpiration exceeds the dehumidifier’s rate of water removal, humidity will continue to build up. In cannabis, the cultivar plays a role in this. Strains with denser buds will require more water removal, and vice versa.
Leaf area index and plant placement density
LAI (leaf area index) is used to measure the amount of plant matter in the space.
This too affects the amount of transpiration, which must be matched by the dehumidifiers in order to effectively control the humidity.
Location and geography
The location and geographical region of the growing facility is important, in order to understand the climate in which it operates.
Outdoor climate conditions affect the climate inside. To best approximate the amount of water vapor that must be removed, factors such as outdoor temperature, humidity, sunlight, rain and wind must be taken into consideration.
Equipment such as black screens and lighting
Humidity is intertwined with other climate factors. To understand the climate inside the growing space it’s important to know how it’s affected by additional equipment. Screens and lighting affect the temperature, which determines the level of relative humidity. Without taking these into consideration, the dehumidification may be insufficient to control humidity. Screens and lighting affect the temperature, which determines the level of relative humidity. Without taking these into consideration, the dehumidification may be insufficient to control humidity.
Additionally, black or thermal screens are a necessary part of climate control. In order to achieve the best results for humidity control, the space should be closed as best as possible, when necessary. This allows maximum control and provides the best results.
Additional machinery such as HVAC or heating pipes
Heating and cooling are an essential part of greenhouse and indoor cultivation. As temperature determines relative humidity, these greatly affect humidity as well. In order to tailor humidity control to the facility, it’s extremely important to factor in the operation and capacity of these systems.
Controlling humidity with DryGair
DryGair is a leading dehumidifier manufacturer, with years of experience in horticulture and in the cannabis industry. To ensure the best results, DryGair tailors the number of dehumidifiers, as well as their models, to the growing space. This is done by factoring in each of the aforementioned parameters, in order to accurately match the airflow capacity and water removal rate the space and grow requires.
Growers around the world use DryGair to control humidity in various climates, growing methods and crops. These are a few real-life examples of cannabis greenhouses that use DG to successfully control humidity:
1.A 1,500 square meter cannabis greenhouse located in a desert climate manages to maintain a relative humidity level of 60-70 by using two standard DG12 units. The greenhouse is not heated or cooled but excess heat is removed at dusk.
2.A California cannabis grower uses one DG12 unit per 1,000 square meters in one greenhouse, with the others left untreated. While the untreated greenhouses experienced fungal outbreaks, the greenhouse treated with DryGair was unaffected. The greenhouses are located in a climate with cold winters and hot summers.
3.A 2,600 square meter Oregon greenhouse that was retrofitted from flower to cannabis cultivation uses 3 DG-6 heating and cooling units as its main climate control system. It’s not only used to control humidity, but to provide an extra increase or decrease in temperatures, when necessary. The greenhouse is located in a cold climate, but during the winter, manages to maintain a comfortable temperature 15oF warmer than outdoors. The fact that the unit utilizes hot water from a preexisting boiler makes it simple to utilize and very efficient.