How To Prevent Mold When Storing Cannabis

Whether growing your cannabis indoors or outdoors, the arrival of harvest time is extremely rewarding and celebratory. You have overcome all of the challenges facing you. You battled back the pests, maintained decent humidity, pruned your marijuana plants to perfection and gave them all of the light, nutrients and water they needed to survive. However, the final stages are not yet complete.

You must now successfully dry out your cannabis and cure it correctly in order to store it safely. This part of the process must not be underestimated or rushed due to the excitement of harvest time. Doing it right will stop any nasty mold or mildew from forming on your valuable buds and potentially ruining your stash.

Mold can be a massive hassle for growers throughout the entire process of growing a crop, from the seedling stage all the way through to bloom and harvest. Because mold has a preference for damp and wet conditions, crops cultivated within humid and warm environments are more predisposed to mold infestation. However, the dreaded threat of mold does not cease when harvest has ended. Mold can still strike, perhaps even more heartbreakingly, when cannabis crop is in storage. Imagine seeing your plants through an entire grow season, only to pull out your stash jar to find a large network of mold growing over all of your hard work.

Causes of Cannabis Mold During Storage


When cannabis is taken from the curing room, it is generally free from mold as long as the producer has taken the necessary precautions in preventing it. At this point, however, the cannabis will be transferred to containers and this is when it can be exposed to higher humidity levels. This exposure to humidity will persist for the life of your product as you continually open and close the product’s container. This will also put your product at risk of mold.

There are two types of mold you hear about when discussing impacts to consumer’s health. The first, more commonly found while your cannabis is in production, is known as “bud rot” or Botrytis cinerea. The second is Aspergillus.

  • Botrytis cinerea is known for its destruction of the cannabis plant itself. It works from the stem outwards, starting as grayish-white wisps that eventually kill the bud, turning a dense cola into squishy, moist plant matter. Bud rot is only found on the plants and is most common in dense colas that receive little airflow and can retain moisture. It cannot develop on cannabis plants after they have been harvested.
  • Aspergillus is a very common mold that can be found on more than just the buds of the plant. When found in high concentrations in the air, Aspergillus spores can wreak havoc on those with damaged lungs or weakened immune systems. It is commonly found in soil or anywhere with a high moisture content, including the buds of a cannabis plant. Unlike bud rot, Aspergillus can affect cannabis plants during storage.

How To Spot Mold On Your Harvest

The most common way mold is recognized on cannabis is though hyphae.
Hyphae are long white/gray web looking strands that can appear anywhere on the bud or stem. Once mold spores land they use hyphae to spread a root system for more nutrient/moisture absorption.

Mold spores are present in each part of the grow process. Since cannabis is organic matter, it is impossible to completely insure that it will always be protected from mold or bacteria.

All cannabis will eventually begin to decompose, which is why aged cannabis is often avoided. Decomposition cannot be completely stoped, but you can make buds last longer by controlling humidity. Common methods include dehumidifiers, regulating temperature through ventilation, and keeping light exposure to a minimum.

Mold’s Effects on Cannabis and Human Health

When your cannabis is exposed to mold, it is rendered useless. Smoking a cannabis product with mold can cause serious harm to the consumer, especially if they have a compromised immune system. As cannabis pushes forward as a medical product, the concern surrounding mold and contaminants is of utmost importance. Cannabis with mold should be discarded in its entirety to protect consumer health.

Cannabis with high levels of Aspergillus can result in harmful infections. High concentrations can lead to the development of an aspergilloma, which can cause symptoms ranging from a basic cough to severe fatigue and hemoptysis. To those with weakened immune systems, Aspergillus exposure can turn into invasive pulmonary aspergillosis, which can spread to other parts of the body besides the lungs, and is capable of resulting in death if not treated properly.

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Cannabis with bud rot also contains spores that can cause damage to your lungs, yet bud rot is not associated with risks as severe as Aspergillus.

How To Prevent Mold

One of the most important things to consider when storing cannabis is how to prevent mold. Mold can occur in any phase of cannabis and hemp cultivation due to how mold reproduces. It sends microscopic spores up into the air in hopes they will find a nice damp place to land and grow.

Since mold spores are airborne, be sure to take special precautions in each step of the growing process. HEPA filters and ventilation for grow rooms or storage locations is recommended to prevent mold. These filters are highly effective, but can be costly in certain applications. Luckily, they aren’t the only line of defense again mold growth in storing cannabis.

Dry Container

Keeping the storage container clean and dry is key to preventing mold or mildew. The most common storage containers are glass or bpa free plastic.

Lids with rubber seals or air lock features that allow them to remain self contained and air tight. Containers are recommended to be clear/transparent so that the buds can be inspected without having to open the container. This can go a long way in extending the duration of how long they can remain in usable condition.

After a container is empty, it should be cleaned with soap and water. Allow the container to dry completely before using for storage again.

[PRO TIP] Glass is a common choice for storage container because it has less likelihood of scratching. This minimizes the surface area where spores can take hold, which also helps to prevent mold.

Oxygen Absorbers / RH Packs

Oxygen absorbers, or rH packs (Relative Humidity Packets), help prolong the life of stored buds.

Oxygen abosorbers control the moisture content within the container used for storage. These pack maintain moisture within one percent of the rating on the label. Most commonly 55% or 62% for organic consumable goods.

This allows for optimum storage humidity levels and lowers the likelihood of mold growth especially in humid areas.

[PRO TIP] Some growers prefer to vacuum seal their cured buds. This works for short term storage, but does not allow for proper ventilation. If the amount of moisture within the bud is still too high, mold can occur.


A cool, dry, dark place is ideal for storing cannabis long term. The cool (below 75°F) temperature, absence of moisture, and lack of UV light reduces the likelihood of bacterial or fungal growth to prevent mold.

Given that the buds are organic matter, they can not be stored indefinitely. After 6 months in the best conditions they begin to decompose. So it is recommended that they are used before the 4-6 month mark.

Frequency Of Checking

Occasionally, if a foggy film or condensation is noticed within the storage containers they will need to be opened and vented. The more frequently the storage containers are opened the more likely chance mold has to form.
Opening the containers creates a change in pressure and humidity between the open air of the room and the container. Mold spores descend from the open air in the room into the container, landing on the buds, raising the likelihood for mold growth.

This is the primary reason that a clear glass or plastic container is recommended for storage purposes and easy inspection. This will allow you to observe the buds conditions without opening the container.

Warning Signs

If you notice any water droplets, fog, or condensation build up on the inside of the storage jar, take immediate action. The container should be opened for proper ventilation. This is the the last chance you will have to save the buds.

Inspect the buds for white powdery mineral deposits, or white/grey web-like fuzzy growth. This is a sign of mold/mildew growth and buds should be disregarded.

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Salvaging Tips


If you notice any of the above warning signs then you have a few option in salvaging the buds before mold sets in.

  • Quarantine the moist/foggy container
  • Open container for ventilation
  • Remove buds, set aside for further drying/clipping
  • Clean container with soap/water or alcohol
  • Allow container to dry completely, or use a new dry container
  • Clip away any viable signs of white mold (if any other color dispose of bud)
  • Increase airflow on the buds by small fan (preferably near a HEPA filter)
  • Once the buds are dry to the touch place back in dry clean container
  • Store in a separate cool dry dark place
  • Monitor 3-4 times a day to watch for signs of moisture build up
  • Clean all equipment (sheers, trays, gloves) and dispose of any contaminated material (trash bags, gloves, clippings)

Can’t I Just Freeze My Cannabis Buds

Cannabis buds can be frozen for long term storage solution, but this comes with it’s own assortment of problems.

Freezing separates the trichomes from the buds themselves. This drastically lowers the quality of your product. However, Frozen buds are still great for making kief, especially for hash production.

Freezing can also increase the harshness of the taste. Freezer burn can also occur if containers are not sealed 100% securely.

Freezing is possible,but is not a recommended solution due to these factors. A more effective option would be proper crop cycling. Allowing for a constant crop of cannabis in each stage of the growing process. This allows for a consistent stream of production and allows for higher quality control when it comes times for maintaining inventory.

Good Cure Is Easier Storage

A major factor in keeping your buds stored successfully is managing the curing process. Curing takes the majority of moisture out of the buds; thus promoting an environment that will keep for a longer, more sustained period of time. And even though mold will eventually occur in all buds, by following these simple steps you can insure the maximum shelf life for your crop.

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