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How To Avoid Cannabis Mold



As a grower, one of your worst nightmares would be discovering the growth of mold on your weed plants. Once an infestation gains access into your garden, it will most likely spread at the speed of lightning, leaving destruction in its wake. 

The best way to prevent this is to learn how to avoid it, because it really does not have a cure of any kind. In this article, we will give you helpful tips that will enable you to keep this phenomenon at bay.  

Can Weed Grow Mold?

For most weed growers, mold is the furthest thing from their minds.

Unfortunately, mold has an uncanny way of creeping in when least expected! 

Mold can be gotten at any time in your cannabis plant's life and sometimes when you think you’ve successfully gotten through the grow cycle…boom! You get a mold infestation two weeks before, or a few weeks after harvest. Actually, this is the time you are most likely to be affected. 

This is very frustrating because it can render your whole crop unusable and you could incur huge losses if you are growing commercially. All your months of hard work and dedication could go down the drain, just like that. 

Mold on Weed

Whether you are cultivating your weed plants indoors or outdoors, several types of mold could still find their way in. Though several types of mold exist, the two most common ones are mildew and botrytis (bud rot). 

Other less frequent molds that affect cannabis are sooty mold, fusarium, as well as mold in soil. Let's take a closer look at each of these molds. 

White Powdery Mildew 

This white powdery layer initially starts its growth in the foliage but it progressively spreads throughout the plant. The leaves of the cannabis plant will then start to turn brown and yellow, withering till they die. 

Though White Powdery Mildew can affect your plant at any time, even when they are quite small, most incidences happen when your cannabis plants develop big leafy plants as they reduce airflow thus increasing humidity. This is also more likely to occur in small spaces such as a grow tent. WPM is also likely to strike in higher temperatures than lower ones. 

The denser the vegetation on a plant is, the more moisture it will release into the air, especially if you keep watering your plants. This explains why rainforests are usually humid and misty.

Badly infected marijuana plants will develop black spots signifying an acceleration of the reproduction as well as transfer of spores. The coating that it has over the leaves will eventually inhibit the plant from photosynthesizing which leads to the death of the plant. 

How can you avoid WPM?

  • Smart fan placement goes a long way in the prevention of WPM because it simply is not able to grow in a breezy environment. The gentle breeze that the smart fan will blow over your leaves will not only prevent WPM, the plants will also love it and grow faster as a result. 
  • In extreme cases, smart fans might not be adequate to push out the excess humidity. In these instances, investing in a powerful exhaust system that has a strong exhaust fan will ensure all the hot and humid air is vented out and replaced with drier and cooler air from outside of the grow space. 
  • Another way to ensure fresh air gets to all your plants is by defoliating excess leaf cover and creating free passage for air, which will greatly reduce the humidity. 
  • A dehumidifier can also be used to suck the humidity out of your space as well.
  • Last but not least, always maintain the temperature in your grow space at below 80°F (27°C) , or at most, 85°F (30°C) . Any temperature higher than this and you have created the perfect environment for WPM to go crazy! Under these conditions, WPM can cover an entire plant in just a matter of days.

Bud Rot: Botrytis 

 This mold initially grows around the branches and stems of the cannabis plant. This makes it very difficult to detect, which is why you should inspect your cannabis plants every day. Though it is more of a risk during the flowering stage, it can affect the cannabis plant at any time. 

Bud rot typically appears as a white or gray fluffy web though it could also grow in shades of green and blue. It consumes the plant matter of the cannabis plant from the inside out, and what is left behind is a “broken down mush”. 

Black mold on weed

“Black mold” generally refers to many types of mold which have a black or dark green appearance. In cannabis, this mold is usually caused by pests and it affects the leaves of the cannabis plant mainly. To prevent the growth of black mold, constantly check for pests and ensure your grow has proper ventilation.

Why does Cannabis mold happen?

Given the right conditions discussed above, mold is able to thrive in most matter that is organic, which explains why cannabis is also a victim. 

The periods in the life cycle of a cannabis plant when they are most susceptible to mold are:

In the vegetative stage when leaves are big and bushy, As discussed above, the lack of airflow creates the perfect environment for fungus to flourish.

  • In the flowering stage when there is increased enzyme activity as well as increased levels of transpiration. Humid air gets trapped within the cannabis plant around the buds creating the perfect environment for fungus to flourish.
  • Another time fungus can flourish is after harvesting, during the curing period. The biggest risk at this stage is accumulating moisture in the curing jars which will naturally lead to mold developing. To avoid this, dry and cure your buds properly and periodically check the moisture content using a hygrometer to keep these sneaky spores at bay. 

How to Prevent Weed Mold

If you have never had to contend with mold, count yourself lucky and let’s keep it that way!

As preventing mold makes the difference between you having a successful harvest or failed one, employing strict measures will ensure that you keep this catastrophe at bay. 

The simple answer of how you can prevent mold is simply by providing adequate ventilation and fresh air for your cannabis plants. As mold thrives in humid, stagnant conditions, if the air around your plants is constantly moving the mold will be unable to “take root.+”

Tips for Preventing Mold Indoors

  • Fresh Air – Having an adequate exhaust system ensures the air within your grow space is replenished every so often, say every 5 minutes. Measured in Cubic Feet per Metre (CFM), this system should be able to keep your plants free of excess humidity. 
  • Ventilation – Installing a few constantly oscillating fans all-round the grow will prevent the air from being stagnant. The circulating air will reduce the chances of spores landing on an infesting your plants and buds.  
  • Low Humidity – You can use a dehumidifier as well as a hygrometer to ensure the humidity levels of your plants are below 55 or 60%. Humidity higher than this is bound to trigger a fungal infestation. 
  • Monitor your overall leaf mass and defoliate where necessary. 
  • Regularly inspect your plants and especially any fat buds. Noticing that the leaves off your bud are curling in and suddenly drying up is a clear indicator that your plants might have mold, even if the rest of the plant looks good. 
  • If you notice moldy buds, try to harvest the whole grow as soon as you can as y all indications, the whole of it may be compromised. Start the during and curing process to ensure any growth is stopped in its tracks and you save at least some part of your harvest.
  • Maintain your plants at the optimum temperature as leaving your room too hot will encourage some mold like WPM and too cold, others like bud rot and fuzzy white mold. An ideal temperature to set would be 75°F (24°C)  especially in humid situations.
  • Defoliation – If your grow space’s bottom is not getting any light, you may consider removing the larger leaves to ensure that your cannabis plant receives both freely circulating air and adequate light. This process can also get rid of sparse duds that are not developing well to enable the plant to focus “its energies” on growing the healthy ones. 

Mold-Resistant Cannabis Strains for Indoors

Although mold will flourish where the conditions will allow it, some strains are more susceptible to it than others. If you think the chances of your cannabis crop encountering mold are higher than average due to your space or the climate of your location, it might be wise to gravitate towards strains that are a bit more mold-resistant.

Tip: Strains that have shorter flowering periods are less likely to develop mold as their buds spend a relatively shorter period of time in the flowering stage.

A few mold resistant strains that can do well indoors are: 

  • Moby Dick – This strain is a sure winner. It is easy to grow, mold resistant and very potent. It smells like peppermint with old school skunky undertones reminiscent of sativa strains from the 90’s. Oh! One more thing, it has great yields too. 
  • Sweet Tooth – This is another mold resistant strain which has a sweet flavor reminiscent of chocolate and laden with powerful effects. It is very popular and usually fetches pretty high prices. 

Preventing Marijuana Mold Outdoors

Though it is easier to keep outdoor cannabis plants mold free, they are not free from the threat. Just like with indoor plants, allowing too much humidity could do you in. Here are a few things you can do to prevent mold in your cannabis:

Shake your dewy or wet plants thoroughly to rid them of excess moisture especially in the morning or after the rain. Ensuring your buds don’t stay wet goes a long way in preventing mold as well as bud rot. 

When selecting where to plant your cannabis, if possible pick an area that is breezy, and receives adequate sunlight especially in the morning when you need it to dry off any dew or rain. 

Although some factors are beyond your control and starkly in nature’s lap, try as much as possible to protect your plants from cold and wet. Outdoor plants are usually affected in the fall when the buds are dense and fat, creating the perfect atmosphere for mold to thrive.

If the weather does not favor you and it gets particularly cool and wet, or if just one plant happens to get bud rot, harvest your entire crop immediately. Harvesting a little early will be a better scenario than losing your whole harvest!

Mold-Resistant Cannabis Strains for Outdoors

If you are going to grow your cannabis outdoors and the climate conditions you live under are not very conducive in the prevention of mold, the following mold-resistant weed strains may be a good idea: 

  • Frisian Dew – This strain is perfectly suited for outdoor growing, even in the Northern areas and has great resistance to mold. It has incredibly beautiful buds and a great smoke. 
  • Jamaican Pearl – This strain that is fruity-smelling has other great attributes apart from it being mold resistant. It grows well outdoors and also has great yields. It has a great cerebral high that lasts long and will not put you to sleep. Its buds also have beautiful amber trichomes at harvest. 

What to do if you have mold on your weed plants?

No cure will help cannabis that has gone totally moldy, though if caught early you can stop it from spreading to the rest of your crop by early harvest of the unaffected buds. 

In some cases, mild symptoms can be treated by fungicides which have their own disadvantage of altering taste and smell and probably having an effect on the end user, especially if they are applied at the flowering stage. 

If short, buds which have started growing mold are generally not worth saving and should definitely not be smoked as they are very likely to have adverse health effects. 

In most instances, it is best to cut your losses and gather enough experience and knowledge to handle your next grow better. 

If faced with a situation of mold, first ensure you protect yourself when you are dealing with moldy buds or plants. Put on gloves as well as face mask to ensure you don’t breathe in the mold and also don’t spread it from one plant to another. 

Immediate removal of any infected plants is recommended while being careful to not spread the spores to uninfected plants. While dealing with an infestation, consider discarding the whole grow if it is severe. 


Avoiding cannabis mold can be a very tricky issue. Mold’s biggest problem is that it is sneaky and can appear at any time. Mold spores always lurk about in the air, waiting for the opportune environment to land on your cannabis and thrive. It can also be very difficult to detect especially in the early stages, which means it will have spread quite significantly before it is spotted. 

However, it is not all doom and gloom. The solution is quite simple. The best way to prevent mold infestation in your cannabis plants is by preventing excess humidity and providing conducive temperatures. We hope we have shed some light on what you should do to avoid this devastating phenomenon and keep your crop healthy and profitable. 


Sebastian is a passionate advocate of CBD's therapeutic potential, dedicating himself to exploring its diverse benefits. As a seasoned writer, he eloquently shares his insights and personal experiences with CBD, aiming to educate readers about its transformative power. His life's mission is promoting holistic wellness, with CBD at the heart of his advocacy.