Mold and mildew can present a significant issue to indoor growers, no matter what crop they’re cultivating. Even with a careful protocol in place, these common pathogens can make an unwanted appearance – and without quick and careful management, can lead to several more severe and costly issues later on.


Let’s start with a brief overview of what mold is. After all, the Chinese philosopher Sun Tzu advised, “Know your enemy and know yourself.” In this case, we’re going to get to know mold a little better – perhaps this will strengthen our defenses against it.

Mold is a fungus, requiring nutrients and certain growing conditions, just like mushrooms or yeast. While many types of fungi naturally occur in nature and can present mutual benefits for certain types of plants, there are a couple species cultivators need to look out for: powdery mildew and white mold. These are considered plant pathogens, meaning they can swiftly kill even the healthiest plants. Spores enter the plant’s leaves through the stomata, blocking cellular respiration – basically throwing a wrench in the plant’s ability to survive.

These plant pathogens can wipe out an entire crop. All your hard work could go down the drain because of these devastating spores.

Not only is mold harmful to plants, it can also cause adverse reactions and other health issues in humans. Because mold exposure can pose a serious risk to both healthy and immunodeficient individuals, legal markets need to take it seriously. Michigan recalled 48 pounds of medical marijuana in January 2019, partially due to mold contamination. In late 2018, a Canadian company recalled several cannabis productsdue to complaints from customers about moldy flower. These examples are two among many, emphasizing the need for sufficient regulation, growing standards and independent testing across the industry.


The good news is that white mold and powdery mildew is relatively easy to spot – white on green should immediately raise some red flags. Additionally, there are a few sure-fire ways growers can prevent this issue from popping up in the first place.

  • Balance temperature and humidity. Any indoor grower knows that striking the ideal balance between temperature and humidity can present a challenge. Mold spores thrive in warm, moist conditions. Removing its preferred environment stops mold in its tracks. But, between managing light spectrum, watering schedule and soil pH balances, finding this balance may be harder than it seems – and take time and effort to perfect. Read more about managing humidity here.
  • Prevent spikes in humidity. Temperature swings between hot and cold (often from lights being suddenly turned off and on) can result in spiking humidity, and therefore, more condensation on your plants. Mildew thrives in these damp conditions. Growers can keep this from happening with dimmable LED fixtures. They run cooler and are capable of gradually getting darker or lighter. Simply put, LEDs give the grower more comprehensive control over the environment at their indoor facility.
  • Ensure there’s enough airflow. This one is especially important as plant pathogens tend to do well in stagnant, damp areas. Installing fans to ensure the appropriate amount of airflow in your facility is one of the first (and easiest) ways to prevent mold or mildew growth.
  • Enforce strict protocol. Anytime you walk through a field of damp grass, there’s the potential you’re carrying spores. Cannabis businesses need to prevent contamination from the outside world – even a careless mistake can lead to pricey consequences, like a full-blown white mold issue. The best way to avoid contamination is by establishing vigorous protocol and strict hygiene standards.
  • Experiment with spectral tuning possibilities. Beyond eliciting incredible physical responses from your plants, adjusting the light spectrum could introduce a novel defense against plant pathogens as well. Early research is promising; a 2016 study found red light spectrum kills powdery mildew. Blue light was shown to slow down or reduce the severity of certain plant diseases, leading some to believe spectral tuning could play a role in holistic agricultural disease management.

While mold and mildew can present a formidable challenge for any grower, it is preventable and swiftly managed with the right tools, approach and mindset.