Mold in Your Cannabis? Here are the Top Reasons and Solutions

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Moldy weed is every cultivator’s nightmare. Here are the top reasons behind moldy cannabis and some helpful solutions.

[/vc_column_text][vc_row_inner row_inner_height_percent=”0″ overlay_alpha=”50″ gutter_size=”2″ shift_y=”0″ z_index=”0″][vc_column_inner width=”1/1″][vc_single_image dynamic=”yes” media_width_percent=”100″][vc_column_text]Cannabis can play host to a slew of nasty organisms, just like every other living thing on our planet. Don’t let your carefully cultivated plants fall victim to mold. Below you’ll find a few simple measures you can take to prevent and manage parasitic fungus (mold).[/vc_column_text][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column width=”1/1″][vc_column_text]

Know your molds.

Molds are microscopic fungi present in virtually every environment. And they’re essential. Molds break waste and plant matter (fallen leaves and dead trees, for example) into small particles before returning them to the soil to naturally fertilize the earth. 

But for people, molds can be problematic. Molds often cause allergic reactions, and in rare cases, death. Mold is also a scourge for cannabis growers (and consumers – no one wants to consume moldy cannabis). There are two types of mold commonly found on cannabis:

White Powdery Mildew

This is a grayish-white coating often mistaken for the sticky, sugary, glittery hairs of trichomes.

You can use your nose to determine whether it’s white powdery mildew or trichomes covering your plants. Here’s how. Powdery mildew smells as foul as it sounds, like the pungent musty, mildewy scent of a damp basement. Sometimes it can even smell like hay or urine.


Botrytis (aka grey mold or bud rot) is harder to detect, but it’s not impossible to find. Botrytis shows up as lifeless brown patches in the leaves.

This lurking mold spreads fast, often infecting a living plant through a wound or opening, causing rapid cellular death. And once this mycelium has germinated, it’s often too late to save the plant.

The devastation these molds can unleash on your grow room is horrifying, and the fact that they can launch spores into the air at an alarming rate and infect neighboring crops is downright chilling.

You don’t want mold on your cannabis crop. But unless you understand what you’re looking for, spotting molds (particularly bud rot) is tricky. It’s not as simple as spotting the green fuzz on the bread in the back of your fridge. 

When it comes to protecting your cultivation facility, you should prevent the outbreak from attacking your plants in the first place. Botrytis control for marijuana begins with prevention, but you can only be sure your crop is free of this common contaminant by performing regular testing..[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column width=”1/1″][vc_column_text]

How do I stop mold in my grow room?

Cannabis thrives in environments mold and mildew love. Still, keeping parasitic fungi at bay is relatively simple if you maintain the proper environment. You can even grow strains designed to ward off mold.

Your best line of defense in mold prevention is understanding a few primary cannabis cultivation best practices. Keep reading to learn about a few of them. 

Keep the airflow going. 

Mold is present in the air at all times. And it doesn’t require much to proliferate. Containing the spread is an uphill battle once mold starts on its wind-blown path of destruction.

That’s why indoor cultivation facilities can benefit significantly from good airflow. Producing enough airflow to rustle leaves gently can make all the difference in keeping molds from settling and spreading. And if you add fans or an HVAC and air filtration system, you’ll also significantly reduce the chance of mold contamination. 

Control the humidity. 

Mold and mildew only need two elements to grow: moisture and organic material. You must keep humidity in check, especially if you cultivate in particularly moisture-rich environments. You should ensure that your relative humidity is no more than 70% (ideally, somewhere between 59% to 63%).

Anything higher, and you run the risk of trapping the moisture that mold needs to grow. You can use a humidor or dehumidifier to regulate excessive humidity. The only downside is that the equipment is pricey for small-scale cannabis cultivation facilities. But here’s a pro tip if money is tight: use inexpensive humidity packs inside your containers. 

Maintain a consistent temperature

Sixty-eight degrees (20 degrees celsius) is the ideal growing temperature for cannabis, and seventy-seven degrees (25 degrees celsius) is suitable for storage. Excessive heat locks in moisture, which leads to mold, and frigid temps can increase moisture exposure. 

Your grow room needs balance. 

Fans can level out temperatures, but if your grow room is too hot, you should consider venting the hot air outside. Also, you should install an air conditioner or evaporative cooler. Choosing the proper light schedules will also help you keep a consistent temp.

Store cannabis in a dark, dry place

How you store cannabis matters.

A cool, dark, dry storage environment will not only maintain the potency and flavor of your cannabis but will also keep out mold. Clean, airtight mason jars are a simple method to limit oxygen and moisture exposure. 

You should avoid plastic packaging because it can degrade crop quality. We also suggest that you keep your plants out of freezers and refrigerators – they’re an open invitation for moisture and mold. And if it’s in your budget, you can always consider investing in a humidor. 

Prune and trim your plants. 

You should diligently prune and trim your cannabis plants. Growing one large “Christmas tree” shaped bud makes the plant more susceptible to bud rot, especially if flowering during high humidity periods.

Regularly trimming your greens can eliminate the unnecessary plant matter that plays host to molds and mildew. Low-stress training (LST) can improve yields and prevent mold growth. LST is a simple bending/tying technique cultivators use to manipulate the plant’s height and shape. Also, this method is excellent for space and light distribution. [/vc_column_text][/vc_column][/vc_row][vc_row][vc_column width=”1/1″][vc_column_text]

Testing your bud is essential.

Today’s cannabis industry is compliance-driven. Every legal state has regulations to ensure consumers get the cleanest, safest cannabis. Some states even inspect for total yeast and mold counts (TYMC) to detect fungus quantities. 

Of course, ingesting and inhaling moldy weed isn’t ideal. Moldy weed leaves consumers vulnerable to many ailments, from headaches and vomiting to acute lung infections.

Customers need to know that what they are purchasing is safe. And as we’ve noted before, third-party testing isn’t perfect. Breaking into the cannabis industry isn’t easy. Don’t throw your hard work, reputation, and licenses away with contaminant violations. [/vc_column_text][/vc_column][/vc_row][vc_row][vc_column width=”1/1″][vc_column_text]

How to detect mold in cannabis with Gemmacert

As you figure out how to prevent mold in a grow room, GemmaCert can keep your cannabis safe and your business flourishing. By the time you notice mold on your plants, it is too late, but with the GemmaCert Pro, you can mitigate the risk. By taking Water Activity readings during the cultivation process and post-harvest you can determine the risk of mold development in your crop. To perform an accurate Water Activity analysis, use the GemmaCert Pro to test small buds collected from 2-3 different sections of each cannabis plant you’re cultivating.[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column width=”1/1″][vc_column_text]

Cannabis mold FAQ

Can weed mold? Absolutely. You’ll need to know a lot more than that, however, to prevent mold on weed as you cultivate your sticky, aromatic buds. To finish up, let’s answer some common questions regarding marijuana mold prevention and how to identify cannabis mold that may already be present:

1. What does moldy weed look like?

Once a moldy weed plant is far-enough gone, mold becomes easy to visually identify. Before mold on cannabis leaves or buds gets bad, though, moldy weed might look just like normal weed—except under a microscope. If you look at cannabis closely enough, you can learn everything about its chemical composition, and you can even learn if it contains mold you wouldn’t be able to see with the naked eye.

2. Does mold on cannabis smell?

You can’t rely on being able to identify mold on marijuana using smell alone. The fruity aromas of budding cannabis tend to block out other smells that might be wafting through your grow room, making it necessary to use professional analytical tools if you want to be absolutely sure your weed is mold-free.

3. How do I decide what to do with moldy weed?

Most growers simply choose to destroy any parts of their cannabis crops that have become moldy. Decarboxylation does not kill mold in weed, and mycotoxins don’t just go away if you make moldy weed into edibles. In some cases, moldy weed may be fit for extraction into cannabinoid isolates, but professional equipment must be used to avoid contamination.

4. Mold on weed vs. mold in weed: Is there a difference?

Whether you’ve found white mold on weed or any other type of mycotoxin, it doesn’t matter if mold colonies are only visible on the surface of your bud. You can be certain that your cannabis nug is thoroughly contaminated with mycotoxins if mold is noticeable anywhere on its surface. Cutting away just the moldy part of the bud isn’t enough, but it’s sometimes possible to amputate a moldy branch of a cannabis plant while saving the rest.

5. Is mildew on weed common?

Yes, mildew is just as common on weed as mold. Usually not visible in large clusters until it reaches advanced stages, mildew can be even harder to visually identify on cannabis buds and plants than mold, further underscoring the need for effective analytics throughout the cannabis cultivation process.

6. How do you tell powdery mildew vs. trichomes apart?

Powdery mildew and the natural trichomes cannabis produces can look a lot alike. Under even a small handheld magnifying glass, however, trichomes will look like delicate, crystalline balls while mildew will look like clusters of spidery spores. Cannabis analytics devices like the GemmaCert Pro can easily distinguish between mold and trichomes.

7. What is black mold vs. gray mold in cannabis?

Gray mold, or Botrytis, is one of the two types of mycotoxins that commonly attack cannabis plants. Black mold, however, is not a common cannabis pest even though it can sometimes be found in grow rooms. Both types of mold can be prevented via effective climate control and early detection.

8. What is cannabis bud rot?

“Bud rot” is another term for the grayish damage that occurs when a cannabis bud becomes infected with Botrytis mycotoxins. Once Botrytis infection has reached the point of being visually identifiable as “bud rot,” the bud in question is no longer safe, and neighboring buds should also be removed. Any plant that has been affected by Botrytis must be tested regularly throughout the rest of its life cycle to prevent any further infections.

9. What are some final cannabis mold prevention tips?

As you figure out how to prevent mold in a grow room, we’ll leave you with a few final tips:


  • Weed molds come in various forms, so make sure to do your research
  • Effective cannabis cultivation climate control methods prevent mold
  • Don’t wait until mold is visually noticeable—test your plants early and often

[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column width=”1/1″][vc_column_text]GemmaCert can keep your cannabis safe and your business flourishing.[/vc_column_text][vc_button button_color=”color-210407″ size=”btn-lg” border_width=”0″ link=”|title:Contact%20Us”]Get in touch today to learn more![/vc_button][/vc_column][/vc_row][vc_row row_height_percent=”0″ back_image=”23134″ overlay_color=”color-jevc” overlay_alpha=”50″ gutter_size=”3″ column_width_percent=”100″ shift_y=”0″ z_index=”0″ el_id=”book_call”][vc_column width=”1/1″][vc_column_text]

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