Medically Reviewed by
Jason Crawford

Article Last Updated on January 18, 2023

The appeal of weed among cannabis consumers is a direct result of its two most important cannabinoids, THC and CBD, which are responsible for the psychoactive, sedative, and anti-inflammatory effects of weed, among others. Moldy weed, however, is not as appealing.

Moldy cannabis buds are often present among illicitly produced weed – which can also contain residual pesticides, fertilizers, fungicides, and pathogens. However, moldy marijuana isn’t a problem only for marijuana cultivators who sell on the black market. Even legal dispensaries and licensed cannabis growers can have a problem with moldy cannabis buds which may be dangerous to the health of cannabis users.

This article will focus on all you need to know about moldy cannabis and how you can spot mold on your stash as a user, as well as prevent mold growth on your cannabis buds as a grower, so read on.

What Is Mold?

Mold is a fungus which reproduces fast via airborne spores. Ingesting mold in small quantities isn’t dangerous to your health as your immune system will prevent any damage, although larger quantities of mold can be detrimental.

The most common mold types are:

  • Botrytis cinerea (bud rot);
  • Powdery mildew;
  • Cladosporium;
  • Penicillium (Penicillin).

Mold is common to a lot of flowers and plants, and it’s the same with cannabis plants, so stick with us to find out how you can prevent it.

How Does Mold Develop in Cannabis Plants?

The reasons for growing moldy weed are various and are often a result of increased humidity and improper ventilation systems in grow rooms. The ideal breeding ground for mold is often created as a result of overly humid rooms and improperly dried weed placed in airtight containers or mason jars. And if you think that getting rid of mold is no big deal, think again! Eliminating mold spores isn’t an easy task since they can survive intense heat and reproduce fast. Moreover, some molds produce mycotoxins which are carcinogenic.

What Happens if You Consume Moldy Weed?

As we already mentioned, poor air circulation and humid conditions in the grow room together with improper ventilation create the ideal breeding ground for mold spores, a cannabis grower’s worst nightmare. And given that mold spores aren’t destroyed at high heat, decarbing won’t get rid of them. 

Moldy cannabis can cause an allergic reaction in people who are allergic to penicillin, and some molds may even produce carcinogenic mycotoxins.

Moldy marijuana may also cause immunocompromised people to develop lung infections, which can be a huge problem for medical marijuana users. Other molds can cause a fungal infection and other health problems which is why moldy weed needs to be thrown out immediately.

What Types of Mold Can You Find in Cannabis?

The most common types of mold found in weed include:

  • Powdery mildew;
  • Bud rot.

Powdery Mildew (White Mold)

Powdery mildew resembles young trichomes which is why it can be mistaken for trichomes by inexperienced cannabis growers. Powdery mildew or white mold thrives in grow rooms where there’s not enough airflow. Powdery mildew spreads quickly and can spread to your whole yield if you don’t get rid of the infected cannabis plants immediately. 

Botrytis Cinerea (Grey Mold) 

Botrytis cinerea, bud rot, or grey mold as it is often called, is a type of mold that develops from the inside out. Grey mold occurs as a result of too much moisture being trapped inside the colas. Signs of mold development can be limp colas, dying leaves, and parts of the cannabis plant not thriving.

As opposed to powdery mildew, bud rot doesn’t require you to throw away your whole plant if it gets infected. You only need to remove the affected parts and save the rest of your cannabis plant.

In indoor cultivation, grey mold is a side effect of overly moist and humid cultivating conditions, while white mold in outdoor cultivation can be caused by heavy rainfall.

How Can You Check for Moldy Weed?

To see whether or not your cannabis plants are mold-free, you can use some of the following methods.

Look at Your Stash Carefully

To figure out if you have moldy weed on your hand, you need to carefully look through your stash. Generally, moldy cannabis can be spotted by the naked eye. The presence of powdery mildew can look like kief, and common signs of mold can also include dark spots on your buds and some slimy parts on your cannabis plant. Weed flowers covered with webbing should also be thrown out as it can be caused by spider mites. 

Smell Your Stash

Terpenes are the aromatic compounds in weed responsible for your weed smelling like an exotic fruit, a pine tree, or a whole array of other scents produced by terpenes. However, moldy weed smells musty, wet, and leaves a sour taste when you smoke it. 

Even though sniffing your stash isn’t a foolproof way to detect mold since some molds don’t produce a smell, and others don’t cause a foul smell in the first few days after the infestation, it can be a helpful way to figure out if you have bad cannabis on your hands.

Use a Microscope or a Magnifying Glass

Mold on cannabis that has been recently infested can’t be seen with the naked eye, which is why you may need to use a magnifying glass or a microscope to check for mold spores in the buds. It’s also useful to place your buds under a black light since mold looks very green once it’s illuminated by black light.

You can also browse the Internet to find out what different types of molds look like so you can have a reference when comparing with what you see under the microscope.

Final Thoughts and Preventing Moldy Cannabis

There are a few steps you can take to ensure you grow mold-free cannabis. One of them includes growing your cannabis plants under the right conditions. That means optimum humidity levels, an appropriate temperature, proper nutrition and lighting, and regular mold inspections throughout the growing process. The optimum humidity levels in your grow room should be between 59% to 63%, and they should be tailored depending on the strain you’re growing.  

Mold can also appear on improperly cured and dried weed, which is why you need to allow your flower to dry off completely before you place it in an airtight container or a glass jar for curing. To get properly dried weed which has preserved the terpene and cannabinoid content, the drying process should last at least seven days.

Dried and cured weed should be stored in a cool, dry place which isn’t the fridge or the freezer (since they can both produce mold as a result of extensive moisture). The adequate storage temperature for cannabis plants is below 77 degrees Fahrenheit.

Finally, make sure that you check your cannabis regularly for the presence of mold as it can cause serious health problems to marijuana users.

A passionate advocate for the benefits of cannabis. Fraser Horton, who has a background in botany and a strong love of nature, has spent years researching how cannabis affects the body and mind. He established Leaf Nation in 2020, where he has devoted himself to educating people about the legalisation of marijuana and its safe and responsible use. Fraser is committed to highlighting cannabis’ potential for improving wellness and working to dispel the stigma associated with its use.


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