5 Marijuana Cultivation Risk Factors - Humidity

Greenhouse Growing Environments, the Future for Cannabis

Leading modern Greenhouses use similar technology to Tantalus Labs

Growing Cannabis (marijuana) is not simple. Growers are faced with managing a multitude of factors to ensure the growth of their crops into healthy mature plants, reflected by the final quality of the buds. This article is part of a series addressing some of the challenges growers face in cultivating high-quality Cannabis. In the concluding article of the series, we will address some of the solutions Tantalus Labs is implementing to ensure an environment supporting the plant’s ability to thrive in an ideal way.


Excess humidity pollutes Cannabis with mould and disease. When designing a Cannabis cultivation system, humidity and its associated risk of mould can threaten crops. This has recently been topic of contention in the Canadian Cannabis cultivation industry, with several product recalls from highly specialized commercial producers. These risks can be mitigated through cultural protocols, but they also hang on the design of the cultivation environment itself.

When growing cannabis indoors, many factors need to be considered to optimize the cultivation environment. This is true with any approach to growing Cannabis, but it is particularly important for indoor environments, as the grower is playing mother nature. The plants are reliant on that grower for every element of environmental support. Modern cultivators are beginning to implement sophisticated software models that include sensor-based data collection. This modern grower is achieving a deeper understanding of how swings in humidity can create a climate that allows moulds to proliferate.

Swings in humidity lead to a climate that allows moulds to get a foothold and proliferate.

There is an innately greater humidity risk when cultivating indoors. At a commercial scale, huge investment in specialized equipment is needed to maintain a stable climate for growth. When using multi-ton HVAC units, lighting, cooling, heating, and dehumidifying, the issues that cause excess humidity compound greatly.

Air Conditioning (AC) units are used to stabilize temperature while the lights are on, and constant cycling of this unit is required for cooling. This pulls humidity from the air as it moves across the fan coil, lowering Relative Humidity (RH), which then needs to be artificially raised via a fog system (depending on humidity targets). Large banks of High Intensity Discharge (HID) lighting are needed to attempt to replicate sunlight indoors, and when these lights shut off daily there is a latent spike in humidity.

This spike is due to the fact that the high thermal energy radiating from the bulbs represents a cooling burden for the AC. Once this heat is removed (ie the lights shut off and the air cools) RH that may have been 45% can double to 90%. This all happens without a change in the amount of moisture in the air.

Trying to combat this daily occurrence with very large dehumidifiers or a heating and venting strategy is a struggle on its own. That struggle is augmented when accounting for the other pieces of equipment that encourage humidity in a closed room.

Plants are constantly transpiring, which also releases water vapor. Every watering adds humidity through evaporation. Factor in Natural Gas burners to boost CO2 levels and an indoor grower is effectively adding 2 cubic feet of water vapor for every cubic foot of natural gas burned. This is on top of an already highly humid environment.

These humidity-intensive practices lead to high humidity and its related risk in sealed rooms. Spores are everywhere. Closed indoor environments are always at risk for moulds such as Powdery Mildew.

This pathogen is most likely to grow in high nighttime RH and low daytime RH, with temperatures in the 22 - 27c range. It quickly spreads in areas of low light and poor air circulation. Indoor rooms that exhibit these conditions in conjunction with high risk microclimates, the issue of humidity is likely to become a persistent problem. For growers that are entrenched in the indoor environments that confine their cultivation programs to these limitations, the options are limited. Some have been forced into hostile remediation methods such as irradiation, as opposed to a more preventative and design-oriented approach.

Some have been forced into hostile remediation methods such as irradiation

Contamination risk minimization and humidity minimization go hand in hand. High humidity levels and equipment that risks sudden humidity spikes often contribute to moulds such as powdery mildew. In an environment that consistently exposes plants to these risks, often irradiation is the only option. Tantalus Labs believes that a design built to passively minimize such risk is the best first line of defence.