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Preventative Measures for Microbial Growth

What Are Microbes & What Do They Do?

Microbial growth in cannabis can be a dangerous thing. “Microbes” don’t just mean bacteria – they can be yeast, mold, fungus, and more.

cannabis growhouse with lights
Image by JR Byron from Pixabay

Aspergillus, a type of mold, is one particularly focused on microbial as it is known for its harmful effect on humans (Centers for Disease Control and Prevention, 2019). When inhaled by someone with a compromised immune system, aspergillus spores “can cause an infection in the lungs or sinuses which can spread to other parts of the body” (Centers for Disease Control and Prevention, 2021).

However, there are so many other types of harmful microbes that focusing on Aspergillus doesn’t entirely protect humans (Ross, 2020). Yes, aspergillus is an important thing to test cannabis for, but so are the other dangerous yeasts, molds, and funguses like penicillium, fusarium, E. coli, and more (Montoya et al., 2020).

Ideal Conditions for Microbial Growth

Humidity and temperature are hugely important when it comes to microbial growth. In truth, when tested, about 10% of cultivated cannabis fails the microbial contamination test (Kern & Green, 2019). This could happen at any point in the cannabis’ lifetime – microbial growth could happen during growing, drying, curing, storage, and transport, and can even happen inside the product’s final packaging while on the retail shelf or sitting in a consumer’s home (Kern & Green, 2019),

“There are two points in the cannabis supply chain when failure of the microbial contamination test is most likely:

  • Testing that occurs post-harvest on cured products that have not yet been packaged

  • Testing THAT occurs on products after they have been packaged. They may have even passed the microbial contamination tests before packaging” (Kern & Green, 2019).

Essentially, a passing grade on the microbial analysis test is meaningless if the cannabis is packaged and stored in a way that allows for microbial growth, which may happen more often than we think (Kern & Green, 2019). The City of Denver proved just this – they conducted random assessments at about 25 dispensaries to test for yeast and mold issues in store-bought cannabis products (Mitchell, 2019). They have reported that out of the 25 dispensary samples, 20 had “at least one or more hold and quarantine orders for cannabis flower, shake or pre-rolled joints” (Mitchell, 2019). It was an 80% failure rate (Mitchell, 2019).

As Jacklyn Green and Roger Kern argue, “When you consider the large-scale environmental conditions in which the cannabis is grown, harvested, dried, cured, and stored and compare it to the internal microenvironment of the packaging, it makes sense that similar environmental conditions would affect the packaged products in the same way” (2019).

Basically, it is vital to ensure that cannabis is packaged to maintain its quality and potency.

How to Prevent Microbial Growth in Cannabis

So the next natural question is - how does one prevent (or at least, minimize) microbial growth in cannabis?

Well, because there are so many opportunities for microbial growth within cannabis’ lifespan, the answer is complicated. For growing specifically, Bart Schaneman with MJBizDaily recommends maintaining a clean growing environment, ensuring the humidity, temperature, and airflow are all at ideal levels, and checking your plants regularly for signs of microbial growth (2022). If there is an outbreak, he writes that it’s important to “contain the spread or destroy all the plants, sanitize the facility, and start over” (Schaneman, 2022).

Once cannabis leaves its growing environment, other similar measures must be upheld to maintain its quality and potency. That applies to the trucks it’s transported on, the rooms it’s kept in, the packages it is packaged in, and more.

The Importance of Testing for Microbial Growth

However, testing for microbial growth is what helps guarantee that a safe, reliable product reaches the consumer's hands. Even if all of the proper standards are met in cannabis’ cultivation, transportation, packaging, and storage, an untested piece of cannabis runs a huge risk of maintaining unsafe levels of microbial growth.

Trust in Steep Hill Illinois

We are proud to be a part of a network of Steep Hill labs that consistently use science to help build a safe cannabis community. Whether you are interested in laboratory testing, data analysis, or consulting services, you can always rely on Steep Hill Illinois to assist you with accurate, reliable results on the latest cannabis production practices. Email us today at to get started!


Centers for Disease Control and Prevention. (2019, December 5). Aspergillosis statistics. Centers for Disease Control and Prevention. Retrieved March 31, 2023, from

Centers for Disease Control and Prevention. (2021, January 8). Where aspergillosis comes from. Centers for Disease Control and Prevention. Retrieved March 31, 2023, from,other%20parts%20of%20the%20body.

Kern, R., & Green, J. (2019, December 29). It's not too late: Post-Harvest Solutions to microbial contamination issues. Cannabis Science Tech. Retrieved March 31, 2023, from

Mitchell, T. (2019, November 4). In random mold tests at 25 Denver dispensaries, 80 percent fail. Westword. Retrieved April 2, 2023, from

Montoya, Z., Conroy, M., Vanden Heuvel, B. D., Pauli, C. S., & Park, S.-H. (2020, August 25). Cannabis contaminants limit pharmacological use of cannabidiol. Frontiers. Retrieved March 31, 2023, from

Ross, Kimberly. (2020, March 31). How to detect and prevent microbial contamination in cannabis: Going beyond compliance testing. Analytical Cannabis. Retrieved March 31, 2023, from

Schaneman, B. (2022, March 22). Best practices: Microbial matters. MJBizDaily. Retrieved April 4, 2023, from

Image by <a href="">JR Byron</a> from <a href="">Pixabay</a>



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