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Humidity in grow rooms is primarily influenced by two factors: transpiration and temperature. As plants grow, they naturally release water vapor into the air through transpiration. In closed environments, this vapor accumulates quickly, potentially reaching saturation levels.

Relative humidity (RH) is the relationship between the amount of water vapor in the air and the temperature. At lower temperatures, air can hold less moisture, causing RH to increase. Even minor temperature drops can lead to humidity spikes, which may result in condensation forming on cool surfaces like railings, pipes, or even the plants themselves.

Maintaining control over humidity is essential for creating the ideal growing environment. By sealing the grow space and utilizing dehumidifiers, growers can regulate their climate more precisely. This helps maintain an optimal Vapor Pressure Deficit (VPD), an important measure of plant health, which should typically range from 0.8 kPa to 1.2 kPa depending on the cannabis strain and its growth stage.
Controlling humidity also prevents condensation and the development of fungal pathogens like botrytis and powdery mildew. Additionally, a controlled climate ensures greater consistency across the growing space, leading to uniform crops in terms of both quality and yield.

By consistently operating in a closed system with optimal climate conditions, 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. 

To achieve the best results with humidity control, it’s important to understand that dehumidifiers have an operating capacity in terms of: 

• Water removal
• Airflow 

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:

• Facility size 

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.

• Plant cultivar

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 (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 (HVAC and heating pipes)
  

Heating and cooling systems have a direct effect on relative humidity. It is crucial to consider the capacity and operation of these systems when designing a humidity control plan.

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. Desert Climate Cannabis DryGair (1500 m2)
Using two DG12 units, this facility maintains a relative humidity of 60-70%, despite being located in a desert. Excess heat is removed at dusk, allowing for stable humidity control.

2.California Cannabis Grower (1000 m2)
One greenhouse, equipped with a DG12 unit, successfully avoided fungal outbreaks while the untreated greenhouses experienced issues. The facility operates in a region with cold winters and hot summers, showcasing DryGair's ability to maintain ideal conditions across climates.

3. Retrofitted Oregon Greenhouse (2600 m2)
This facility, previously used for flower production, was converted to cannabis cultivation using three DG-6 units. In addition to humidity control, the system provides heating and cooling, maintaining a 15°F temperature difference in cold winters, utilizing hot water from an existing boiler system.

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