how to prevent mold on 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.

PSA: Check Your Cannabis for Mold

Spotting mold on bread or cheese is pretty easy, but on cannabis? Not so much.

Here’s everything you need to know about what to look for, whether it’s safe to smoke moldy cannabis, and how to keep your stash mold-free going forward.

Moldy cannabis usually has a grayish-white coating. If you’re not a seasoned consumer or grower, though, it can be easy to mistake trichomes for mold and vice versa.

Trichomes are those sticky, shiny crystals on the leaves and buds that give cannabis its aroma.

Unlike trichomes, which look like little hairs that almost appear to glitter, mold has a gray or white powdery appearance.

Mold also has a distinct odor to it, so your nose may notice the mold before your eyes do. Moldy weed usually has a musty or mildewy smell, or it may smell kind of like hay.

It probably won’t kill you, but it’s still not recommended.

In healthy people, smoking moldy weed isn’t likely to have a detrimental impact on your health — barring the general risks of smoking, of course.

If you smoke moldy weed, you might experience symptoms like coughing, nausea, and vomiting, which are more unpleasant than dangerous.

But if you’re allergic to mold, you could end up with inflammation of your sinuses or lungs and symptoms like:

  • sinus pain
  • drainage
  • congestion
  • wheezing

In people with weakened immune systems or lung conditions, inhaling smoke from weed that contains certain mold species can have serious health consequences.

Fungi like Aspergillus, Mucor, and Cryptococcus can cause serious and even deadly infections in the lungs, central nervous system (CNS), and the brain in people with compromised immune systems.

A UC Davis study found these and other types of potentially harmful fungi on cannabis samples bought from dispensaries and growers in Northern California.

You may be tempted to cut off the obviously moldy bits and smoke the rest, but it’s not a good idea. Life’s too short for bad bud.

If you can see mold or mildew, you’re better off tossing it. It’s not going to taste or smell good anyway, and could make you feel sick.

Storage is everything when it comes to preventing mold.

Exposing cannabis to the wrong temperature, light, humidity, and oxygen can promote the growth of mold.

Here’s what you need to keep in mind.

Avoid the fridge or freezer

Forget what you’ve been told about storing your green in the fridge or freezer. The temperatures are too low, and the exposure to moisture can result in mold.

The ideal temperature to store cannabis is just below 77°F (25°C).

Use the right container

Glass jars with an airtight seal are the way to go if you want to keep things mold-free.

Mason jars and similar glass containers help limit the exposure to oxygen and moisture, which can prevent mold and keep your nugs fresh longer.

If you want something a little more sophisticated than a Mason jar, most dispensaries sell containers designed for this exact purpose.

Keep it in a dark, dry place

Direct sunlight and moisture are recipes for disaster when it comes to keeping cannabis fresh.

The sun’s rays can heat things up and hold in moisture. A damp environment can also cause too much moisture to build up if your container isn’t properly sealed.

Keep your container in a dark, dry cabinet or closet that doesn’t get too hot.

Mind the humidity

Cannabis is best kept at a relative humidity of 59 to 63 percent. Go any higher and you run the risk of trapping moisture and growing mold.

Adding a humidity pack to your container can help. These are little packets that contain a mix of salts and water that help regulate the humidity in your container. They’re inexpensive and last a couple of months.

Humidors made specifically for cannabis are another option if you want to get fancy and are willing to spend some extra bucks.

Like most green things, cannabis can develop mold under the right conditions. Learn what to look for and whether there's any way to salvage your bud.