Cannabis Mold: How to Disinfect Indoor Grows

Battling mold is one of cannabis cultivation’s greatest ongoing challenges. Today, with testing requirements becoming more widespread and stringent as the legal market progresses, growers are being held to an ever-higher standard to protect consumer safety.

With thousands of potential microbial threats ready to take root in your crop, it’s critical to take a strategic, upstream view of cleaning and disinfection protocols.

Indoor growing: a perfect environment for mold

Indoor grows and greenhouses of any kind are hotbeds of microbial activity due to the warm, moist air they create. Adding cannabis to this environment – a crop whose flower is especially susceptible to mold – makes for a unique challenge.

What’s more, the process of harvesting cannabis adds to a grower’s risk for outbreaks. Trimming and drying flower, employees that move from room to room to manage plants, these are all common triggers for fungal spread.

Cleaning vs. disinfection vs. sterilization

Growers know they should clean their rooms between harvests to prevent issues. They may disinfect tabletops, maybe even wash the floors and walls. These are good processes and important to avoid buildup. But cleaning alone is just removal of mostly dirt and debris. It doesn’t kill pathogens that lead to disease, pests, or contamination.

Disinfection, which destroys pathogens or potential pathogens on surfaces and objects, is required to decontaminate cultivation facilities and crops, and more fully avoid mold outbreaks.

Sterilization goes one step further than disinfection. It works to achieve a quantifiable level of disinfection making an object or space suitable for specific use, such as medical tools that will be used in human surgery. This is rarely necessary for a grow. Instead, decreasing hazards through proper cleaning and disinfection will ensure a safe cannabis product.

Three cleaning best practices

A regular cleaning schedule, properly communicated and managed by staff, is a great standard operating procedure (SOP) for an indoor grow or greenhouse. Consider a few best practices in developing your cleaning protocols:

1. Remove soil, dirt, dust and organic material regularly. If using a vacuum cleaner, use a high-efficiency particulate air (HEPA) filter to avoid mold spread.
2. Clean from the top down. After removing larger material, begin at the top of your space to remove debris. Remove big piles as they build up, so they don’t spread.
3. Remove biofilm from irrigation systems. These important tools for cultivation are also one of the biggest culprits for mold outbreaks. Clean with a selective oxidizer like chlorine dioxide (ClO₂) at a concentration as low as 50 ppm, or products with hydrogen peroxide (H₂O₂) mixed with peracetic acid (CH₃CO₃H) at 800 ppm.

Above all, remember that timing is everything. Cleaning between harvests is one of the best ways to ensure a new crop isn’t carrying mold baggage from crops past.

Top disinfection protocols

The critical step of disinfection can be more time consuming than simply cleaning, but as mentioned above, it’s crucial to the mitigation of mold.

In any disinfection process, of course, pre-cleaning is required. Removing organic material on surfaces or objects treated will allow the disinfectant to do its job.

Some tips:

1. Start with the end in mind. Are you trying to prevent mold or mitigate an outbreak? That answer should guide your disinfection protocols.
2. Consider your surface. Your disinfectant will need a period of contact time to impact the pathogens it is trying to kill. A porous surface may not hold a liquid in one place as long and should be treated differently. The risk of corrosion should also be factored in. Common disinfectants like bleach can cause corrosion over time on stainless steel tables favored by many indoor grows.
3. Know the disinfectant types. Not all disinfectants are created equal. You’ll want to know which microorganisms you’re trying to kill so you can match it to the disinfectant.

Most of all, ideally buy products based on efficacy and safety. Your products for disinfection should be approved by the Environmental Protection Agency, for example, and include a label that you can read for specific kill claims and instructions for use. Otherwise, you run the risk of losing a crop you tried to disinfect, simply by using something not effective, or by using an effective product incorrectly.

Integrated pest management

An integrated pest management (IPM) strategy is an ongoing way to manage mold within a cannabis cultivation facility.

On top of the protocols already mentioned, consider additional methodologies if mold continues to be an issue.

Fungal monitoring, for example, can help identify problem areas of a grow. Spore traps are set around a facility and tested by a lab to see what kinds of molds are growing. These insights are critical to developing specific protocols tailored to a unique grow.

Avoiding cross contamination is also key. Controlling who enters a room, ensuring proper protective equipment is worn, and carefully managing trim rooms will help keep mold from spreading.

In addition to liquid cleaning and disinfection, growers are also using gas products to clean rooms between harvests. Products that include ClO₂, for example, can work to improve air quality overall.

Consumer safety at the forefront

The cannabis market is growing, and with it comes more regulation aimed at protecting consumers. Growers must be able to leverage professional, proactive facility management to meet compliance.

And the investment is worth it. Effective IPM programs work to prevent problems before they start.

Avoiding the destruction of a harvest due to mold outbreak can save thousands and even millions worth of product to your grow. Even more importantly, prevention keeps you and your customers safe.

Bernie Lorenz, PhD, is chief science officer for ProKure Solutions, and an industry advocate for sustainable, transparent and clean cannabis grow methods. As one of the industry’s most seasoned experts on IPM programs, he led the effort to develop a new ASTM International standard aimed at establishing cleaning and disinfecting protocols for indoor and greenhouse cannabis cultivation facilities.