Grow Hack: Odor Control Strategies & Their Best Applications

Sweet, skunky, minty, fruity—the aroma of cannabis is an essential feature of the crop and often our first inclination of its quality and characteristics. Cannabis’ odor is created by terpenes, oil-producing compounds that play a major role its psychotropic effects via complex interactions with cannabinoids.

While an essential part of the plant, terpenes create challenges for commercial cannabis growers. Most municipalities restrict how grow operations handle odors. Particularly in urban areas, regulations may prohibit a growroom or greenhouse from venting untreated air outside. This introduces a major challenge for growers. Ventilation is the primary way growers control heat and humidity. Without it, indoor growrooms and greenhouses are can easily get too hot and humid, increasing the risk of pests, molds and diseases.

As large-scale cannabis operations proliferate, the need for cost-effective odor control methods is mounting. Commercial cannabis growers must provide sufficient cooling and air circulation without exhausting untreated air outside. Home growers, too, typically want to reduce odors to keep their crops discreet. Thus, the need for odor control spans many operations. From time-tested to cutting-edge, here is a roundup of odor control strategies and their best applications.

Carbon Air Filters (The Standard)

Carbon filters (AKA carbon scrubbers) have historically been the go-to method for serious odor control. These use pellets of charcoal to trap terpenes as air passes through the filter. Carbon filters are simple to install, effective and reliable, if changed regularly. The major disadvantage is that they must be replaced frequently, usually every 2-4 months. This is doable for home growers or small-scale commercial producers, but can get quite costly on larger scales. For example, when designing their 120,000 sq. ft. greenhouse near Vancouver, Canada, Tantalus Labs required significant airflow to help reduce their use of chemical pesticides. If using a carbon scrubber system, each bay of the greenhouse would require 17 additional fans with carbon filters The initial investment was significant, but more cumbersome was the maintenance and operational cost of replacing 160 filters and fans every couple of months. The carbon filters also reduce airflow through a fan, necessitating more fans than originally planned. All in all, the system turned out to be impractical for the large greenhouse.

While costly on large scales, carbon filters are still the highly effective for home growers and indoor growrooms. In these cases, the grower installs a carbon scrubber in ducting before air moves through the exhaust fan. Filters should be sized to meet the size of fan (described in cubic feet per minute or CFM). Performance is inhibited by higher humidity, making them better suited for cultivation facilities with some environmental control.

Air Filters

Standard air filters, often called air purifiers, are typically made of densely woven fiber screens. These trap particles as air circulates through the filter, which can either be a stand alone unit or incorporated into a ventilation system. Filters are less effective than carbon scrubbers for odor control. They are primarily employed to trap larger particles, such as dust and molds in the growing environment. Odor control can be a small or moderate secondary benefit. Advanced ones, like HEPA (high-efficiency particulate arrestance) filters can get quite pricey.

Sealed Greenhouses (For Commercial Growers)

Due to the costs of odor control for large-scale grows, some commercial greenhouses are taking another approach entirely: reducing the need for ventilation in the first place. Instead of exhausting air outside, sealed greenhouses circulate air inside. Fans and advanced climate control systems regulate indoor conditions such as temperature, CO2 and humidity, and provide sufficient air circulation.

This strategy has a number of other benefits: it reduces incoming pests and pathogens; saves CO2 and energy; and avoids the possibility of hemp pollen entering the structure and pollinating crops, a recent issue in legal states like Colorado. However, enclosing a greenhouse raises other challenges with controlling over-heating and humidity. Companies are quickly responding with innovative climate control solutions to enable a sealed indoor environment. Ceres Greenhouse Solutions, for example, builds insulated cannabis greenhouses for harsh climates like Colorado. Their Ground to Air Heat Transfer (GAHT) system circulates air through a network of pipes underground. The air is cooled and dehumidified as it passes through the soil, and then exhausted back into the greenhouse cooler and drier.

Creating a super controlled environment with advanced climate controls—including heating, cooling, dehumidification and air movement—is a major trend in commercial cannabis greenhouses. This enables growers to keep odorous air inside, while still providing precise environmental control and sufficient air movement. Back-up ventilation systems with carbon scrubbers can be much smaller, allowing for initial and ongoing savings. You can read more about the pros and cons of a sealed greenhouse on Ceres blog on the topic here.

Odor Neutralizers (For Home Growers)

Odor neutralizers span a broad range of products. These can be as simple and cheap as the air freshener in your car: these products simply cover up the smell, without eradicating it. More effective solutions are gels and oils ,which waft into the air and bind with terpenes.  Ona gel products are popular with home growers. These adsorb terpenes, eliminating cannabis odors. Importantly, they cannot be used directly in the growroom as they will negatively affect the taste and smell of the product. Instead, they should be placed in adjacent living areas. Thus, they are limited to home growers, but considered effective for that application.

Ozone Generators (Not Recommended)

Ozone generators are a longtime tactic to deal with odors, but generally considered risky, if not downright unsafe. Ozone is a gas made of three oxygen atoms that breaks apart and bonds with terpenes. In significant concentrations, it is toxic to both plants and humans. For people, it’s a lung irritant, and can produce a slew of health effects. For those reasons alone, many growers advise against using ozone as an odor control strategy. Others proclaim generators can be used safely because they are limited in how much ozone they can produce over a time period, making high concentrations less likely. (The challenge is that the gas can easily build up in a room if there is not sufficient ventilation.) Regardless of how you interpret the research, ozone generators are a less common strategy for those reasons, and one that demands caution for both the grower and the crop.

Biofilters (One to Watch)

Due to the high cost of odor control on a commercial scale, growers are innovating in the rapidly growing commercial industry. Tantalus Labs turned to the livestock industry for solutions for their large-scale greenhouse. Biofilters are have been used for years as an odor control strategy for farms and municipalities. A biofilter is simply a stockpile of organic material, like woodchips, inoculated with bacteria that naturally consume odorous molecules.

Though this strategy has been proven to reduce odors from methane, Tantalus Labs commercial is undergoing the first tests to evaluate how bacteria process terpenes, and thus eliminate odors. Initial small-scale tests by biofilter companies showed promise. They also assuaged concerns that the bacteria would harm the health of cannabis crops. Currently, the first biofilter application is being tested in the company’s 120,000 sq. ft. greenhouse near Vancouver.

Tantalus Labs’ trial raises an important point: though odor control is not the sexiest topic, it is ripe for innovation. Currently, traditional methods are challenging to implement cost-effectively at scale. In this highly regulated industry, controlling odors of this incredibly aromatic plant is a topic that is here to stay.

Don’t miss our previous Grow Hack: Wind Barriers for Growing in Dry, Breezy Areas