Here’s a headline that caught our eye recently:
“Cannabis flower recalled due to mold contamination.”
Don’t get us wrong, we were glad to see that officials in California were on the case, and we’ve been happy to see similar stories from other legal states.
But we couldn’t help thinking that ten or twenty years ago it would have been a fantasy to imagine state agencies issuing recall notices for hazardous batches of cannabis.
In the past, consumers were always on their own when it came to finding and tossing moldy weed. And to be completely honest, most of us still are.
Whether you live in an “illegal” state or you buy from dealers in legal states; whether you grow your own plants or simply keep your stash around for a while, mold is enemy #1.
So it’s still important to know how to spot moldy weed and what to do if you find it.
Why Does Weed Grow Mold?
Mold spores are just about everywhere, and mold grows everywhere there’s a welcoming host. It’s even appeared on plants grown on the International Space Station .
But one of the plants extremely susceptible to mold growth is cannabis.
Mold loves to grow in moist conditions — and cannabis is full of moisture, particularly while it’s still growing and has just been harvested. Most types of mold also flourish in high humidity, which can be an issue in grow rooms, many outdoor climates, and stash boxes.
How common is moldy weed? Very common.
One study published in the Journal of Allergy and Clinical Immunology found that 13 out of 14 samples of cannabis purchased from dealers contained mold. Another study summarized in the journal Clinical Microbiology and Infection found a laundry list of fungi growing on 20 samples of medical marijuana purchased at dispensaries in Northern California.
That means, to paraphrase a cliché made famous by ESPN anchor Dan Patrick many years ago: You can’t stop mold, you can only hope to contain it.
We’ll talk about ways to do that shortly.
How to Recognize Moldy Weed
The best way to avoid winding up with moldy weed is to buy your flower at a dispensary, which should inspect its product before selling it. However, even that approach isn’t foolproof. Always look for the telltale signs of mold before buying, and before using.
The most common mold that grows on weed is powdery mildew. It can initially look like kief dust but it’s thinner; you can even blow some of it off the bud. Powdery mildew can also look a bit thicker, like confectioner’s sugar.
Other types of mold can have different appearances: gray, white, brown, or yellow fuzz; dark spots that look out of place in the buds’ natural colors; gray or white threads that look like spider webs. Slime may also be detectable on the flower.
Some forms of mold can be problematic to detect because they look much like the trichomes you want to see on your weed. The best way to be sure if you have a problem is to use a black light, which will highlight the green glow of mold. (You can use a microscope too, but who has one of those?)
There’s one other way to know if your stash is moldy: smell it. It if has the unpleasant aroma of urine, sweat, or the clothes from your grandmother’s closet, the odor is probably coming from mold. Don’t try this if you’re allergic to penicillin, though. Penicillin and similar antibiotics are made from mold, so you could experience an allergic reaction just from smelling moldy weed.
That may sound like a pain to bother with when all you want to do is smoke up. Here’s why it’s important.
What Happens When You Smoke Moldy Weed?
We’ve already mentioned the danger that mold can pose to those who are allergic to mold-derived antibiotics. But just as many people are allergic to mold in general, they may end up developing a nasty fungal infection in their lungs or throat if they use moldy weed
A study published by the Centers for Disease Control (CDC) found that weed smokers were more than three times as likely as non-smokers to contract fungal infections. And infected smokers who were immunocompromised were more likely to die. Other possible side effects could include lung congestion, wheezing, and sinus pain.
Most of us aren’t allergic to mold, of course, so it’s not usually that serious. Even so, smoking moldy weed often causes sore throats, sneezing, and coughing that is more serious than you might experience after a prolonged smoke sesh. Some people also experience nausea or vomiting.
Two final notes.
First, moldy weed can be just as big a problem for those who are vaping it or making edibles with it.
Second, you don’t have to smoke a lot of moldy weed to experience these problems. Some people may not be affected at all, but others can begin suffering issues after just a few tokes.
We promised to discuss ways to “contain” mold — or in other words, make the environment inhospitable to its growth. Let’s do that now.
How to Prevent Mold Growth
We’ll split this section into two parts, one for growers and one for smokers.
Tips to Prevent Mold in Your Marijuana Grow
It’s important to inspect your plants regularly for early signs of mold growth. It’s by far the best way to protect your crop.
Here are other steps you can take to discourage mold growth on your cannabis plants.
- Buy strains that are suitable for growing in your climate. Environmental stress on plants can hasten mold growth.
- Consider mold-resistant strains like Pineapple Express, Cannatonic, and Hashberry.
- Erect tarps overhead to shield the plants from rainfall, and shake off accumulated dew each morning. Excess moisture encourages mold growth.
- Place windbreaks around your plants. Too much wind can also be an environmental stressor.
- Pay careful attention to the temperature and humidity in your grow room. Relative humidity higher than 60-70% during the vegetative stage will encourage mold to grow; it should be even lower during the flowering stage. Room temperatures should be maintained throughout the growing period.
- Ensure proper air circulation and ventilation. Mold is more likely to grow when air is stagnant.
- Trim large leaves once the plants are large. Too much foliage obstructs airflow and creates a humid environment around the plant.
- Don’t overwater.
- Dry and cure harvested plants properly, ensuring they’re exposed to fresh air regularly.
Tips to Keep Your Stash From Going Moldy
- Forget storing your bud in baggies; use a glass container (like a mason jar) with a sealed cover.
- Keep the stash jar in a dark, dry area where temperatures don’t get above 75° or below 65°.
- Humidity in the stash should be right around 60%. Putting a humidity pack into your jar is your best defense against mold. (Don’t worry, they’re inexpensive.)
Moldy Weed: FAQ
Q: If you discover mold on your weed, should you throw it out?
A: If it’s in your stash, yes. You may think you’ve isolated the problem buds, but mold spores spread quickly and the chances are excellent that there’s more growing — you just can’t see it yet. If you discover mold on a plant you’re growing, try removing the moldy areas and hitting the rest with an organic, all-natural fungicide before tossing the whole plant.
Q: Can mold grow in weed vape juice?
A: It’s not extremely common but it can happen, particularly if your cartridges or juice are old. Expiration dates on some packaged products may not be hard-and-fast, but pay attention to them on your weed and weed carts.
- Punja, Z. K., Collyer, D., Scott, C., Lung, S., Holmes, J., & Sutton, D. (2019). Pathogens and molds affecting production and quality of Cannabis sativa L. Frontiers in plant science, 10, 1120 .
- Kagen, S. L., Kurup, V. P., Sohnle, P. G., & Fink, J. N. (1983). Marijuana smoking and fungal sensitization. Journal of allergy and clinical immunology, 71(4), 389-393 .
- Thompson, G. R., Tuscano, J. M., Dennis, M., Singapuri, A., Libertini, S., Gaudino, R., … & Engelthaler, D. M. (2017). A microbiome assessment of medical marijuana. Clinical Microbiology and Infection, 23(4), 269-270 .
- Benedict, K., Thompson III, G. R., & Jackson, B. R. (2020). Cannabis use and fungal infections in a commercially insured population, United States, 2016. Emerging infectious diseases, 26(6), 1308 .