how to cure moldy weed

How to Avoid Mouldy Weed During Drying and Curing

Ahhh, harvest time! It’s easily the most exciting time on your calendar. Unfortunately, a tiny little mould spore can ruin all your hard work if you’re not careful. In this article, we’ll show you how to avoid mould while drying, curing and storing your weed, so you can enjoy your buds safely.

Don’t let your guard down after harvest—learn how to protect your buds from mould during the final stages of the growing process.


What Makes Cannabis Buds Mouldy?

The mould that can develop on cannabis flowers, colloquially called “bud rot” by growers, is caused by Botrytis cinerea, a necrotrophic fungus that also grows on grapes, strawberries, tomatoes, and other fruits and vegetables.

Botrytis thrives in warm, humid climates and attacks the living cells of plants or fruit, while feeding on the dead matter. It develops on the stems of live cannabis plants or harvested flowers and slowly grows outwards, which makes it particularly hard to spot. Usually, by the time you spot botrytis on the surface of a bud, it will have almost completely destroyed its insides, leaving it wet, slimy, and smelly.

How to Prevent Mould after Harvest

In the grow room, the principles of preventing mould are maintaining optimal temperature and relative humidity, as well as proper air circulation. Post-harvest, you’ll want to follow the exact same principles to avoid losing your hard-earned buds to mould.


Cannabis flowers have a high water content when they are harvested. Therefore, before you light up your buds, you need to be patient and let them dry till they contain only about 10–15% of water.

Drying your buds is as simple as hanging them upside down from a piece of string or clothesline. Where you hang them is completely up to you, just make sure they are in a dry, dark place where the air circulates freely. Growers typically dry their buds in a designated room or a cupboard/closet. If you’re short on space, you can even hang your buds inside a cardboard box; just make sure to poke some holes in the box for the air to circulate.

Creating the Perfect Drying Environment

Ideally, you’ll want to dry your buds at 18–20°C and 50–60% relative humidity. Some growers like to keep the temperature at the higher end of the spectrum during the first 3 days to dry their buds a little faster, before drawing the temperature back down to slow the process. You’ll know your buds are ready to be cured once their stems snap easily. This can take up to 2 weeks, but it will vary depending on the temperatures and humidity levels you’re drying your flowers at.

If it’s hot, we recommend drying your buds in a lightly air-conditioned room. You can also use air-conditioning to drive down the humidity if you live in a particularly humid area. Finally, remember to use fans to circulate the air around your buds to dry them evenly and further prevent mould from forming.


Once your buds are nice and dry, you’ll want to cure them in airtight jars for at least 2–3 weeks (or more, if you have the patience).

As buds cure, they continue to lose moisture, but at a much slower rate. This slow release of moisture helps bring out the aromas and flavours in your flowers and also purges any impurities. Unfortunately, the build-up of moisture inside your curing jars can also create the perfect conditions for botrytis spores to grow.

Trim Like a Pro and Keep Things Clean

Before you cure your buds, you must ensure they’ve been trimmed to perfection. Old foliage like leaves and stems can trap humidity and create the ideal environment for mould. Whether you prefer trimming wet or dry, make sure your harvested flowers are free of unnecessary plant matter before you pack them into your curing jars.

Another key step to preventing mould when curing weed is cleanliness. Make sure your jars are sterile and dry before you start filling them with flowers. Also, only fill your jars to 3/4 of their capacity. Keep your jars in a cool, dry, and dark place (light degrades THC and can drive down the potency of your buds).

The Art of Burping

To further prevent mould when curing weed, we recommend you open (or “burp”) your jars 2–4 times a day to remove and replace the old, humid air. After about 1 week, you can start burping your jars less frequently (1–2 times per day), as the flowers will be dryer and release less moisture.

If you’re worried you’ll forget to burp your jars (or you’re lucky enough to have a huge harvest on your hands), you can use humidity packs to control moisture levels inside your jars. For curing cannabis, we recommend using packs that help maintain 62% humidity.

Keep a Watchful Eye

Finally, the best protection against mould is a keen eye. Make sure to regularly inspect your buds during the curing process. If you suspect some of your buds to be developing mould, separate them from the rest as quickly as possible to avoid the fungus spreading even further.


Once you’ve cured your weed for at least 2–3 weeks, it’s officially ready to be smoked. You can continue storing your flowers in your curing jars, using humidity packs to avoid them drying out too much over time and to maintain humidity inside the jars at optimal level. Remember that your buds will continue curing and their flavours should intensify as they mature, so don’t smoke your way through the stash too quickly!

Keeping Mould at Bay—Bottom Line

It’s vital that you don’t rush your way through the final stages of the growing process. While we know you’ll be anxious to sample your home-grown buds, taking the time to properly trim, dry, and cure your flowers will take them to the next level in terms of flavour, aroma, and potency, all the while keeping them safe from mould.

And if you do find buds that are affected by the dreaded fungus, make sure you remove them and closely inspect the rest, as smoking mouldy weed is dangerous for your body!

Humidity Packs Protect Against Mould

Humidity packs are small and simple tools that pull in moisture from the surrounding environment. When the moisture level starts to climb, they’ll absorb water particles that would otherwise serve as a breeding ground for mould.

Moisture Fighters Offer Two-Way Control

At Royal Queen Seeds, we engineered our own humidity packs specifically for curing cannabis buds. Our Moisture Fighters possess a two-way control mechanism that allows them to both trap and release moisture. This enables them to take in excess moisture while also preventing your flowers from becoming too dry and losing their flavour.

Humidity Control Pack

A Plant-Based Product With No Preservatives

Our Moisture Fighters are crafted with the health of the environment and your buds in mind. Each packet derives entirely from plant-based materials and contains absolutely zero preservatives. You don’t have to worry about any unwanted chemicals leaching out and contaminating your pristine organic flowers.

Humidity Indicators Keep You Informed

Moisture Fighters remove any guesswork from the curing process. Each pack features a card that houses a humidity indicator. This reusable piece of kit will let you know when you need to swap out your Moisture Fighters. Knowing exactly when to do this means you’ll keep the curing environment perfect during the entire process.

How to Use Moisture Fighters

Moisture Fighters are extremely easy to use. Keep your flowers juicy and terpene-rich using the steps below.

  1. Remove Moisture Fighters from their packaging, making sure not to open the Fighter itself.
  2. Place a Moisture Fighter and the humidity indicator alongside your buds in their curing jar.
  3. Let the Fighter do its thing. When the dot on the humidity card turns from pink to blue, swap out the Humidity Fighter for a fresh one.
  4. Reset the reusable indicator back to the pink setting to keep track of the new Fighter.

Afraid of losing your precious buds to mould? Click and read everything you need to know on preventing mould when drying and curing cannabis flowers.

How to identify and avoid buying moldy weed

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  1. What is mold?
  2. What happens if you smoke moldy weed?
  3. How to check for moldy weed
  4. How to keep your cannabis mold-free

Mold is never a welcome sight. Not in bread or cheese, and certainly not in your cannabis. Moldy weed is not only disgusting, it’s dangerous. Consuming mold-infested weed can have some serious adverse effects. But how do you know if your bud’s been infected?

Nearly every legal state has some sort of microbial lab testing requirement for regulated cannabis sales. These tests check for mold and mildew in batches of marijuana. However, even legal markets have seen their share of moldy cannabis over the years.

Read on to learn how to identify and avoid buying moldy weed and how to store weed so it doesn’t get moldy.

What is mold?

Mold is a catchall term for fungus that reproduces via lightweight, airborne spores. Humans inhale or ingest minuscule amounts of mold every day. It is typically harmless in small quantities since a healthy immune system can successfully prevent any damage.

Mold found on marijuana buds, or flower, is the same kind that grows on other plants. Botrytis (responsible for bud rot ), Mucor, Cladosporium, Rhizopus, and Penicillium (the mold responsible for penicillin) are the most common. Mold thrives in humid or moist environments that lack proper air ventilation.

Mold found on marijuana buds, or flower, is the same kind that grows on other plants. Photo by: Gina Coleman/Weedmaps

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In cannabis mold most often develops when the bud isn’t dried correctly, though it can form in earlier stages of cultivation, such as in a too-humid grow room. Improperly dried weed stored in an airtight container for curing creates an ideal breeding ground for mold.

Mold spores are tricky to eliminate. They can survive the intense heat of a lighter when smoking a hit and they don’t burn off in the oven when weed is decarbed. Some molds produce mycotoxins too, which can be carcinogenic.

What happens if you smoke moldy weed?

When you smoke moldy weed, you inhale the fungus directly into your lungs. Those with compromised immune systems are at risk of developing a lung infection. Smoking moldy weed is also dangerous for those with allergies to mold-based antibiotics such as penicillin.

A study published in “ Clinical Microbiology and Infection” 2017 found molds such as Aspergillus, Mucor, and other potentially harmful fungi in cannabis samples procured from northern California dispensaries. By smoking moldy weed medical marijuana patients risk fungal infections and other problems.

The bottom line is moldy weed cannot be made fit for use once contaminated. Always throw away moldy weed, even if your risk for infection is low.

How to check for moldy weed

Thankfully, there are several ways to determine if your flower is mold-free.

Use the naked eye method

Eyeballing your weed is by far the easiest way to check for mold.

Healthy cannabis should be covered in spindly, glittering trichomes. Trichomes are sparkly glands with tiny hairs that appear almost crystalline in structure, separated by distinct trichome nodules with space in between them.

These are significant signs to keep in mind as you visually examine your bud.

Some mold looks like cobwebs in the bud, leaving behind a cotton candy-like webbing that’s gray or white in appearance. This could also be caused by spider mites, but you don’t want to smoke bug-infested weed either.

Another type of mold looks suspiciously like kief but is far from the real thing. Powdery mildew is a form of fungus that leaves a gray or white powder-like appearance. It is usually dull and muted in color, and looks like dust compared to the sparkle of trichomes or kief.

Other mold signs are dark spots, gray or yellow fuzz, or a slimy residue. If you find mildew in your marijuana, quickly dispose of it and check the facility or container where it was stored to make sure it hasn’t spread to other buds.

Use your nose

The countless terpene combinations in cannabis present a wide array of aromas, from dank to exotic fruit to skunk. Moldy weed, however, has a very distinct and unpleasant aroma. Moldy marijuana smells like human sweat, urine, or musty hay, all of which are typically repulsive to the human nose. A quick whiff should tell you whether your weed’s been infected with mildew.

Moldy weed has a very distinct and unpleasant aroma. Photo by: Gina Coleman/Weedmaps

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Sniffing isn’t foolproof, however. Some people are more sensitive to cannabis’ aromatic nuances than others, and some users who are allergic to mold may have a reaction if they sniff too closely. And some molds don’t produce a smell, especially infestations that have only just taken root.

Use tools to check for mold

Consumers can also detect mold in their weed using low-powered microscopes, many of which are cheaply available online. Under a lens, mold produces filaments that look nothing like bubbly trichomes. If it doesn’t look like weed, it might be mold.

Black lights also can help reveal mold spores in your bud. Most mold glows an eerie green when illuminated by a black light, making it easier to identify.

Review brand websites and media for recalls

The best way to protect yourself from smoking moldy bud is to purchase lab-tested cannabis from a licensed dispensary. However, the legal marijuana market is expanding more rapidly than testing facilities and regulations can keep up with. And where legal restrictions still exist, illicitly produced marijuana products can still contain residual pesticides, fungicides, and microbial substances.

Keep an eye on local media, brand websites, and state and city websites for recalls of particular batches of products to help you discover unfit bud.

How to keep your cannabis mold-free

Storage is of the utmost importance when it comes to keeping your bud free from mold. Marijuana exposed to improper temperature, light, humidity, and air risks mold development, but there are things you can do to extend your weed’s shelf life and health.

Storage is of the utmost importance when it comes to keeping your bud free from mold. Photo by: Gina Coleman/Weedmaps

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First, make sure your weed is properly dried and cured. Most professional cultivators should do this right, but when growing your own bud, it’s essential to allow the flowers to dry correctly . The process can take up to seven days and should be done with care in proper environmental conditions. Correctly dried weed will cure successfully, maintaining the perfect balance between dry enough to smoke and moist enough to preserve the terpenes and trichomes. .

Store your bud in a cool, dry place but not in the freezer or refrigerator. It’s too cold, and the exposure to moisture is potentially mold-inducing. The ideal storage temperature for your flower is just below 77 degrees Fahrenheit.

Keep buds in airtight containers made of dark-colored glass. Mason jars and the like limit air and humidity exposure that could encourage mold development. Many dispensaries sell containers precisely for this purpose.

Finally, cannabis requires precise humidity levels to maintain its dry-but-not-too-dry, smokeable goodness . The humidity in your storage jars should stay between 59% and 63% to keep things perfect. You can buy disposable humidity packs, such as Boveda packs, to add to your jars.

How to identify and avoid buying moldy weed Copy article link to clipboard. Link copied to clipboard. Contents What is mold? What happens if you smoke moldy weed? How to