Cannabis and Mould: How to Spot and Prevent it

Mould spores are literally everywhere (even the astronauts on the International Space Station have to deal with it) but for cannabis growers, they can mean the destruction of an entire crop. For consumers, mouldy cannabis could cause respiratory problems or nausea. It’s not life-threatening but it’s not great for your health, especially for immunocompromised individuals. Learn more about mouldy cannabis facts here.

How to Spot Mouldy Cannabis

While sticky cannabis is good, wet cannabis is not. Legal cannabis goes through stringent testing to ensure that mould and microbes are not present, so the final product shouldn’t contain any harmful mould. Mould is usually visible to the naked eye, so if you’re buying cannabis from any source, not just government-regulated channels, then you should be able to spot anything that’s cause for concern. Often dense trichome coverage can be mistaken for mould. If the flower you’re inspecting has a wet feel to it and has patches of white that’s more on the fuzzy side of frosty, it could be cannabis better suited for the compost bin than your lungs. In addition to white fuzzy white spots, brown, black, or gray patches as it could also be a sign of mould. Here are some other tips for spotting quality cannabis.

Sky Pilot densely covered in trichomes with no mould in sight.

How Does Cannabis Get Mouldy?

Moisture lock was historically an issue for illicit market cannabis as improperly packaged products can develop mould in the jar, especially if extra water has been added to increase the weight pre-sale. Health Canada sets moisture limits on legal cannabis that are lower than the norm in the unregulated market. This is to ensure that mould can not grow post-packaging.

Mould is carried by spores and it can appear any time in the growing, harvesting, and curing process, but the last two weeks before harvest are the most critical time. There are two main types of mould that affect cannabis: white powdery mildew and botrytis cinerea (aka bud rot).

Just like the mildew that can develop in under-ventilated bathrooms, mildew appears on cannabis under hot and humid conditions when there is not sufficient ventilation. It appears as a fuzzy white powder with a consistency of flour versus the juicy looking opaque or white trichomes that we want to see.

Plants with lots of leaves tend to be more prone to this type of mould as it’s harder for the air to flow to all parts of the plant, especially the lower leaves. Cramped growing conditions can also contribute to mildew. Careful temperature and airflow control along with pruning can all help to keep mildew in check.

Botrytis cinerea is also known as ‘bud rot’ due to the way that the mould spreads. Instead of being visible on the surface like mildew, bud rot comes from inside the bud and spreads outwards, making it hard to spot until leaves start dying around the bud-- it will appear wet and could fall apart when handled. Bud rot can spread quickly through a plant (even overnight), so it must be harvested as soon as possible to save the plant, and potentially the entire crop. Bud rot occurs in lower temperatures when the buds are too wet. It first appears as a white wispy mould (not to be confused with the flower’s pistils) and turns from gray to black - giving the bud a mushy and slimy appearance.

Mould is generally caused by high humidity, mild temperatures, and poor ventilation in the growing process but can also be caused by factors within the plants such as dense buds and leaves and a weak plant immune system - giving cultivar genetics a role to play in the prevention of mould.

How do Growers Prevent and Treat Mould?

Licensed Producers use a range of techniques to ensure that cannabis is mould-free. While clean growing practises and prevention are the best way to do this, there are various ways to ‘cold pasteurize’ cannabis using radiation. Although this sounds alarming, radiation is used in our everyday life - it’s what makes the radio, TV, cell phones, and microwaves work. Irradiation, using gamma rays, is used on cannabis and also on other food items such as potatoes, onions, wheat, ground meat, and dried spices. It can result in a small loss of terpenes but is a Health Canada approved method of removing any traces of mould. The goal here is safety, and we support that.

Here at Tantalus Labs, we employ growing practices that naturally control humidity, temperature, and airflow. SunLab’s active air filtration allows for maximum airflow and cools the growing environment while preventing stagnant moisture.  We also select strong cultivars that are as mould-resistant as possible.

Airflow is constantly being cycled through SunLab to ensure mould doesn't develop. 

In order to protect immunocompromised consumers, we use e-beams to sterilize our cannabis during the curing process. E-beams (electron beams) are used in the medical field and are safe for food sterilization. There are several differences between gamma rays (irradiation) and e-beams. E-beam sterilization is quicker and has a lower penetration into the materials, and doesn’t cause oxidation, which can occur with irradiation. Oxidation is not harmful but can speed up the degradation of cannabis and affect THC and terpene levels.  

Prevention is better than cure and our goal is to grow clean cannabis, with the additional use of e-beam technology to protect immunocompromised consumers, while protecting the delicate terpene profile of each individual flower.

Tantalus Labs

Tantalus Labs

Tantalus Labs is leading Sungrown, BC cannabis. We created SunLab¹, a facility using natural inputs to grow elite cannabis products.