If you grow cannabis, you probably savor its familiar, pungent scent. Your neighbors? Not so much. Whether you’re growing a few cannabis plants for personal use, or you’re a commercial cultivator with an indoor facility or outdoor farm, odor mitigation is an important issue.
Cannabis derives its odor from terpenes, volatile organic compounds that comprise the plants’ resin. These compounds easily convert from a liquid to a gas which can travel and permeate the air. The scent is strongest during flowering, harvesting, and processing.
Here, Oaksterdam University horticulture experts share insight on how to mitigate that “skunky” smell. While we find this odor pleasant some find it extremely noxious. This should not be overlooked but managed.
Managing Odor in Indoor Cannabis Grows
Controlling odor relies on maintaining the temperature of your facility, scrubbing the air to remove volatile particles, and potentially sealing the garden area where plants are present to keep the compounds in place.
Terpenes begin to release into the air at about 68°F. The higher the temperature, the more terpenes are released. In indoor facilities, keeping the temperature down helps keep more of these terpenes in the plant material, which helps reduce odor as well as preserve the quality of your flower.
Controlling airflow not only helps maintain proper temperature but assists with odor mitigation. The goal is to use fans, filters, and ductwork to direct air and trap odors before they are exhausted. OU Instructor Jeff Hickey recommends grow tents for home growers who are just starting out or who only need to grow a limited number of plants.
“Grow tents come with much of this equipment in place, making it easy,” he says. For larger-scale growers, Oaksterdam’s horticulture program goes in-depth on how to build both open- and closed-loop ventilation systems, and calculate the size of the equipment you need for optimum airflow.
Use Carbon Filters
Regardless of the size of your grow, the tried-and-true component in odor control is the carbon air filter. As air passes through the filter, odor-causing compounds are trapped, while clean, odorless air escapes.
The size of the carbon filter you need depends on the amount of airflow required. For carbon filters to be effective, the air that needs to be “cleaned” must move through the filters at an appropriate rate and at the proper humidity. Filters must be checked and changed frequently to remain effective.
Seal Your Space
Even when using carbon filters and best practices, odors can still escape through small cracks in doors, windows, walls, floors, and ceilings. Completely sealing a grow space is difficult, which is yet another advantage of using a grow tent if possible. Odor-eliminating or absorbing gels, such as ONA, can also help cut down on lingering smells. These materials come in small containers that can be placed near exterior doors or in places where visitors might be able to detect the smell of cannabis. However, these gels cannot be placed near the plants, because they will neutralize the odors of the flower itself.
Dealing With Odor Outdoors
Odor control is far more challenging for outdoor cultivators. In most cases, the best you can do is place the garden as far from adjacent public roadways and neighboring properties as possible. This can significantly reduce the risk of odor nuisance, complaints, and violations.
Catch the Drift
According to OU Horticulture Instructor Eric Brandstad, commercial growers often hire odor control companies to analyze where odor drifts and pools, and who it might affect most, then concentrate on odor control in those areas.
“The idea isn’t to clean the air completely or try to work so hard at getting rid of the smell. It’s really dealing with where the smell goes and who it bugs the most,” he said during a recent Oaksterdam Clubhouse Plant Talk.
Outdoors and in greenhouses, fogging systems and aerosol-type air handlers deal with the smell on a larger scale.
New Techniques in Odor Mitigation
As cannabis is legalized across the country, more commercial growers are focusing on odor control. This is leading to new technologies, says Oaksterdam Horticulture Instructor Jeff Jones. Some technology to watch is the use of biofilters (stockpiles of organic material) and enzyme treatments in exhausted air for large-scale gardens.
Other techniques tie into closed HVAC systems and use ultraviolet light in the UV-C band, which has a neutralizing effect on odor as well as plant pathogens. Ozone, deionization machines, and electrostatic filters are further options.
On a small scale, Jones has considered using hypochlorous acid in a water dunk treatment during harvest to lower odors produced. During Oaksterdam’s Friday Night Hort Labs, OU students have mentioned using mineral oil stretched across fine filament screens that can mine out terpenes. Another technique is to direct air from multiple rooms into a “lung room,” where scrubbing and air purification take place.
No matter the size of your cannabis grow, it’s important to stem the smell.
“I think we need to understand that on a commercial level you can lose your license if you don’t have an effective odor mitigation plan, but even a home grower can cause neighborhood concerns, from what we feel are pleasant odors,” Jones says.
For a deeper dive into setting up ventilation systems, check out Oaksterdam’s Horticulture Program. Classes include Friday Hort Labs, where participants share video tours of their grows and get advice from faculty in real-time.