Behind the Label: Mold scare in cannabis

Behind the Label: Mold scare in cannabis


What’s with all the new ruckus surrounding mold?

Recently, a lot of consumers seem to be worried about moldy product coming from Missouri’s licensed marijuana cultivators.

The origination point of the increased concerns seems to be coming from some individuals testing various products out on the market, that were tested by licensed cannabis testing facilities, like GCA Labs, and showing mold growth similar to the pictures below.

These tests are often being done utilizing the most accessible and affordable option, such as DIY mold test kits that you can purchase online. These kits are not nearly as accurate as the qPCR testing methods used by laboratories. The qPCR methods look for specific mold DNA and extract it from the sample.

Some DIY kits test for “viable”, or living, spores only. These kits use a growth medium that is added to a petri dish. A mixture of growth medium and the sample are mixed and “extracted”.

This product is then placed in the petri dish and set aside for a determined amount of time to allow for microbial growth. These plates are designed to grow mold spores and since there are mold spores in the air everywhere all the time unless you are in a controlled, sterile environment, growth on these plates should be expected, even when extracting from a particular product.

Mold growth on plate

What does the growth on the plates actually mean?

It means there are mold spores in the air where the test is conducted, or possibly the product was contaminated after the official test was completed. The volume of growth on the plate is not indicative of anything beyond how fast that particular spore grows in the type of culture plate provided.

These DIY mold test kit options come with more than a few drawbacks to their use, often including no accredited lab certification or chain of custody for legal verification, inconsistent laboratory results from location choice, uncontrolled shipping/handling, and not being able to account for the environment the test is performed in. As mentioned above, “viable” mold spore sampling media, such as agar, can easily become contaminated when prepared outside of a laboratory setting by individuals without proper training. These samples are also being shipped across the country without the proper chain of custody and quality control protocols, meaning the results, at best, should be taken with a grain of salt, and at worst, are completely unreliable.

What else do these types of tests not tell you, that licensed testing facilities do?

It does not tell you what spores are responsible for what you are seeing. The state has strict guidelines on what type of spores are being tested and which ones aren’t. These types of tests make it nearly impossible to distinguish what is being shown, and where it may have been introduced in the test.

The location of the mold growth, or where the contamination came from. Was this growth due to the area of testing, how it was stored after purchase? All of these play a factor into accurate testing.


These also do not show the mold is producing mycotoxins or other mold toxins. Since mold is naturally occurring in many biomes and is beneficial, tests like this do not distinguish between the good and the bad, or if it is potentially harmful. In fact, individuals can buy microbes to add to cannabis in order to make the plants healthier.

With all these issues are the results from plates useless or misleading?

Yes and no.

While they are not proof of a problem (or of safety) and can’t be determined if action is needed, they do indicate mold was introduced somewhere. They just don’t when, where, how, or why.

These types of tests are not advised by trade organizations within the mold industry. Mold industry trade groups, such as the American Industrial Hygiene Association (AIHA) and the American Conference of Government Industrial Hygienists (ACGIH), do not recommend DIY mold testing kits.

The EPA recommends that “Sampling for mold should be conducted by professionals who have specific experience in designing mold sampling protocols, sampling methods, and interpreting results.”

Even organizations such as Consumer Reports, have consistently advised against the use of DIY mold testing kits, finding them to be unreliable.

It is great to see so many cannabis consumers worried about their health and paying more attention to their products, the safety, and testing!

The cannabis testing facilities can always test products for consumers, and answer questions related to the testing.

With many individuals trying to enter into the industry in any way possible, make sure to vet any potential vendor or tester to help ensure you are getting the most accurate and safe products and results.

If you have any questions regarding mold testing feel free to reach out to us at or find us online at