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Types Of Mold Affecting Cannabis: Tips To Prevent And Eliminate Mold In Your Cannabis Garden

Added 21 April 2023

Did you know that NASA recently discovered that even plants grown in outer space could develop mold if the conditions are too humid? Experts aren’t sure how mold can get up there, but it does. That’s how notorious mold can be for plants, especially your cannabis plant. 

But even though mold began its life 1.5 billion years ago and experts have discovered over 100,000 species of it, you only have to worry about a few varieties (or species) of it when growing cannabis plants. 

So, what types of mold do you need to worry about when growing cannabis? Learn all about the various types of molds on cannabis and how to deal with them in this article below. 

What is Mold?

What is Mold?

Mold is one of the biggest threats to cannabis plants, and in most cases, it is difficult to spot until it’s too late. But what is it, really? Mold is a type of fungus encompassing a variety of species. 

Mold spreads in spores that multiply rapidly upon finding the right environment to form a network of small filaments called hyphae. However, since mold lacks a digestive system, it relies on external matter for food. 

Once it takes hold of your plant, it starts secreting enzymes that break down the plant matter. This is bad as your plant literally starts rotting. But mold isn’t all that bad — it plays a crucial role in the ecosystem by acting as a natural decomposer for dead plant or animal matter. 

However, when it infects your plant, it’s a recipe for disaster for your plant and yield. You don’t want it to decompose your plant. 

Mold usually grows where there is moisture — high humidity is a breeding ground for it. Therefore, if you don’t maintain your plant’s environment well, you risk a mold infestation. And since it acts quickly, it is often difficult to eradicate it from your plant, and in worst-case scenarios, you may have to toss your plant in the bin. 

What causes mold, its various types, and what you can do about it — learn more on this further in the article.

What Causes Mold on Cannabis?

What Causes Mold on Cannabis?

Humidity is home for mold, so if your cannabis plant or the grow room is humid or moist, mold can grow there. But there is more to this than just high humidity. Here are some reasons mold may grow on your cannabis plant. 

1. Your Plant is Big and Leafy

As a cannabis grower, your goal is to grow the bushiest plant you can — who doesn’t want that? But this is not always a good thing. If your local climate is humid and your cannabis plant grows bushy, i.e., big and leafy, it may not get enough air to reduce the humidity levels.

In such cases, the deep interiors of the canopy can get a little too humid, where mold can start breeding quickly. This also happens in cannabis plants that do not get enough aeration or fresh air in the grow room. 

A big, leafy canopy is one of the primary reasons mold can grow on your plants. So, to avoid this, you must ensure that the relative humidity in your grow room is at ideal levels, the canopy is well aerated, and if required, you should consider pruning your plants to improve aeration. More on this below.

2. Your Plant is in the Late Flowering Stage

When your plant is in the late flowering stage, it will grow many buds that will be close to maturation. When this happens, the buds grow big and bushy — another breeding ground for mold. 

The bigger the buds are, the more prone they are to develop mold. 

Generally, if a mold spore lands on the bud, it makes its way inside and starts developing since it is very moist. Once mold has grown on the buds, it is impossible to get rid of it.

If your buds are riddled with mold, you can easily spot the problem with symptoms like discoloration, white fuzzy formations, or the buds appearing gooey or ugly. 

At the same time, it is not recommended to consume moldy buds in any way. Mold can have nasty health implications, so it is best avoided. It can lead to lung diseases, nausea, vomiting, and much more. 

If your plant experiences bud rot, the best thing you can do is discard the plant immediately while isolating other plants from it. You must also check the other plants for any sign of mold development. Remember, mold is easy to spread, so you must avoid it in any way, especially when your plant is in the flowering stage. 

3. Improper Drying or Curing Stage

Even after the cannabis plant has been harvested, it is not entirely mold-free. During the curing and drying stage, you must ensure your buds dry quickly enough to not develop mold but not so quickly that they get crunchy. 

This is a tricky stage, so you need to first understand the best drying and curing process for your cannabis buds in accordance with your local weather. For instance, if you live in a humid environment, you must dry the buds accordingly in a humidity-controlled environment. On the other hand, in an arid region, you can be a little lax.

What are the Types of Mold Affecting Cannabis?

What are the Types of Mold Affecting Cannabis?

When speaking of mold, most people consider mold to be of a single kind, but as mentioned earlier, there are thousands of species of mold. A few of them are harmful to your cannabis plant. Here is more on the different types of mold you may encounter on your cannabis plant.

1. Botrytis 


Botrytis, also known as bud rot or gray mold, generally develops on buds, especially in outdoor gardens with high humidity levels or rainfall. It can also happen due to poor storage or open wounds on the plant.

Typically, this mold enters the bud and stays dormant until the environment is humid enough to sustain its growth. Once it gets humid, the mold spore starts multiplying rapidly and growing outwards — within a night or two, the mold can completely take over the bud and start rotting it. 

Like many other types of mold, botrytis also secretes enzymes that decompose the cell walls of the buds, and according to experts, this mold even triggers the host plant to self-terminate the cells.

Since it stays dormant and multiplies quickly, this mold is tricky to identify at first, and when you spot it, it is almost always too late. Here are some of the symptoms of bud rot:

  • The leaves near the cola may turn yellow, shrivel or start dying 
  • The buds may look discolored, limp, or develop gray fuzzy specs 
  • Infected plant matter crumbles when touched and feels dry 
  • Dark mold growth within the buds 

Since there is no way to fix this problem — you have to toss the buds in the trash — which is why it is always better to avoid bud rot in the first place. Here are some tips to help you prevent bud rot in your cannabis plants:

  • Keep your grow room and all the equipment clean and disinfected, especially before pruning 
  • Sterilize your tools after every use 
  • Control the indoor humidity levels so the grow room does not get damp 
  • Invest in an air filtration system to keep the air in your grow room as clean as possible
  • Follow the right curing and drying methods so your buds don’t stay exposed to high humidity or take too long to dry 

Follow these tips, and you don’t have to worry about bud rot in your cannabis plants as much. 

2. White Powdery Mildew

White Powdery Mildew

The second most common type of mold that can attack cannabis plants is white powdery mildew. As the name suggests, this mold is white — if your plant suffers from this issue, it may look like someone sprinkled some sugar on it. 

Just like bud rot, powdery mildew also thrives best in high humidity, and can affect cannabis plants in both vegetative and flowering stages. One of the first symptoms of WPM is the formation of white fuzzy spots on your plant along with the leaves wilting or discoloration. 

Generally, you will find this mold on the surface of buds and leaves. But the difference between botrytis and WPM is that the former grows within the buds while the latter grows on the surface. 

At the same time, you mustn’t confuse WPM with trichomes that naturally grow on the buds and leaves. Trichomes glitter and appear like small hairs, whereas mold simply appears fuzzy white or gray. 

Other symptoms of powdery mildew include disfiguration of your plant, stunted growth, distorted leaves, discolored plant tissue, etc. 

Fortunately, this mildew isn’t as bad as bud rot. Yes, it can still kill your plant, but unlike bud rot, mildew can be treated as long as it is in the early stages of infection. Once it takes over your plant, it is not worth treating it. 

The easiest way to deal with WPM on your cannabis plant is to use neem oil as a foliar spray. If required, you should also prune the infected parts to completely eliminate the mold from your plant. 

And to avoid powdery mildew from growing on your plant again, you should follow these steps:

  • Keep adequate distance between your cannabis plants to prevent mildew transmission 
  • Keep your grow room well-ventilated and control the humidity at all times 
  • If required, invest in a dehumidifier to bring down the relative humidity of your grow room 
  • If you are growing cannabis outdoors, use a spot that gets the most amount of sun and a decent amount of air 
  • Ensure the soil has excellent drainage (protip: mix perlite to improve aeration) and avoid overhead irrigation 

3. Root Rot

Root Rot

The third type of mold that you may encounter as a cannabis grower is bud rot, specifically fusarium. This type of mold is common in hydroponic cannabis plants since the root system is almost always drenched in water. But this can also occur in soil-based plants if you overwater them. 

Since this mold affects the roots, it is not as transmissive as other types of mold, but it can significantly affect your plant’s growth. Root rot can render your plant's roots ineffective, making it difficult for your plant to absorb nutrients, eventually leading to death. 

Some symptoms of root rot include wilting of leaves, nutrient deficiencies, brown spots or yellowing of leaves, roots or stems may turn red, and the roots may turn slimy, swollen stem, brown vascular bundles within the stem, etc. 

Unfortunately, root rot is difficult to treat, and while you can try flushing your plant and cleaning the roots, it is often ineffective in treating the problem. In such cases, your best bet is to cut your losses and toss the plant entirely. And if you plan to use the soil again, you must treat it with hydrogen peroxide to completely eliminate any mold spores from the soil. 

While treating it may be difficult, with basic steps, you can easily prevent root rot from affecting your plant in the first place. Here are some tips to prevent root rot in your cannabis plants:

  • Ensure the soil is aerated and is getting enough oxygen 
  • Use fans in your garden to keep the moisture levels in control
  • Keep your grow room clean and sterile at all times
  • Only use high-quality grow mediums that are well-treated and free of contaminants
  • Ensure the soil or the growing medium has enough drainage to prevent the pooling of water
  • Rotate your crops regularly since root rot can also occur in stagnant soil 
  • Check your plants for any signs of mold infestation often

4. Sooty Mold 

Sooty Mold 

The final type of mold that can be commonly found on cannabis plants is sooty mold. However, unlike other molds discussed above, sooty mold does not directly attack your cannabis plants via spores. Instead, this form of mold is spread via the secretions of pests like aphids or whiteflies

Some common symptoms of sooty mold include small black patches on the leaves, slow growth of plants due to impacted photosynthesis, sticky infected areas, yellowing of leaves, etc. 

If you find sooty mold growing on your cannabis plant, you need to look for the pests that are causing it. You then need to eradicate the pest from your garden, followed by flushing and cleaning your cannabis plant. 

In most cases, organic pesticides like neem oil work well enough to eradicate pests from cannabis plants, but sometimes, you may have to use dedicated pesticides if the infestation is severe. 

How to Prevent Mold in Cannabis?

How to Prevent Mold in Cannabis?

As mentioned above, mold is a notorious problem for cannabis plants and is often impossible to eliminate. In most cases, the only thing you can do if your plant is suffering from a mold infestation is to discard your plant and start anew. 

But with the right growing methods and some nifty tricks, you can protect your cannabis plant from mold effectively, so you don’t have to ever throw your plant in the trash can. How do you do that? Follow these tips to prevent mold from getting on your cannabis plants.

1. Maintain Ideal Humidity Levels

Mold grows best in damp conditions with high relative humidity, so the best way to prevent mold on cannabis plants is to keep the humidity levels in check. Ideally, you must maintain the humidity levels at:

  • 65% to 70% during the seedling stage
  • 40% during the vegetative stage, reduced gradually from the seedling stage
  • 30% to 40% during the flowering stage 
  • 50% during the drying stage and 60% during the curing stage

Remember, when changing the humidity levels, only change the RH by 5% per week so you don’t shock your cannabis plant. 

2. Prune Your Cannabis Plants

The next best way to prevent mold on cannabis is to prune your cannabis plants. By pruning off unnecessary parts of your cannabis plant, you can improve light penetration and aeration within the canopy without affecting the plant’s growth — this can effectively prevent mold.

Another benefit of pruning is that it allows your plant to divert the nutrients where they are required the most instead of supporting other parts. The result would be a better yield by a significant margin. 

3. Use a Fan and Ventilation to Keep the Air Fresh

Apart from humidity, the air must also be fresh and clean. So, you must use fans and ventilation to keep the air fresh in your grow room. For small setups, even a small table fan or an oscillating fan works wonders to keep the air fresh, but if you have a more elaborate setup, you can invest in an air conditioner and a dedicated fan and ventilation system designed specifically for plants. 

4. Use Neem Oil

Neem oil is one of the best pesticides and fungicides for your cannabis plant. If you catch the infestation in time, it prevents pests and fungi from growing or multiplying further. 

To prepare a neem oil pesticide at home, use one teaspoon of neem oil for a liter of water, mix the solution well, and use it as a foliar spray. Make sure you do a patch test. If the concoction is too strong, it can cause more harm to the plants. There are many instances of growers losing their plants to neem just because they didn’t mix it well. The oil can remain on the leaves and prevent the leaves from transpiring and may eventually kill them. 

Therefore, mix it properly, and remember not to spray the buds with neem oil since it can leave a harsh aftertaste. You should stop using neem oil three weeks before the harvest. 

5. Grow Mold-Resistant Strains

Genetics plays a major role in your cannabis plant’s health, one of which is how well your plant can resist mold or fungal attacks. So, if you live in a humid or warm climate, you should play it safe by choosing strains that are more resistant to mold. 

Some popular mold-resistant strains are Sweet Tooth, Moby Dick, Frisian Dew, and Jamaican Pearl. But if you can’t find any of these, just choose a strain with a shorter flowering cycle since they are less likely to develop mold. 

Summary: Types of Mold Affecting Cannabis: Tips To Prevent And Eliminate Mold In Your Cannabis Garden

Mold can come into your plant’s life with a surprise. It shows up when you least expect it, and if you don’t act fast enough, it can completely ruin your crop within a few days. 

And what makes it worse is that dealing with mold is difficult, and in many cases, the only option for the grower is to cut their losses and discard the plant. Even if the plant is close to maturity and almost ready for harvest!

This is a frustrating experience. Imagine putting months into growing a perfectly healthy plant, only to have it develop bud rot during the final weeks of flowering. So, if you are growing cannabis and want to keep your cannabis plant safe from mold, you must employ some strategies to avoid it at all costs.

The best way to avoid mold on cannabis is to keep the humidity levels in check as per your plant’s growth stage and local environment. The next thing you must do is ensure the air in your grow room is fresh, and if required, you must also prune your cannabis plant to improve aeration.

At the same time, you must use high-quality substrates with excellent aeration and drainage capabilities so the roots don’t develop root rot or get suffocated. You must also keep your grow room sterile and clean at all times and avoid wearing outdoor clothes indoors as they can carry the spores easily.

Instead, isn’t it easier to prevent mold? So, use the tips mentioned above to prevent mold on your cannabis plant, and don’t forget to regularly check your plant for any signs of mold. 



Excellent information! I had at least 3 crops with mold with two weeks to go before cutting, the relative humidity in Argentina in winter is more than 60%, even with a small dehumidifier it gets complicated! Damn mildew


Nice timing :rolling_on_the_floor_laughing:


unless you amputate, can't get rid of WPM. Even if you do something to clean off the surface of the leaf, there's still a mycellium network that will regrow. You can only slow it down. Removal around the infected plant material early on gives you a fighting chance to avoid it. if you re soilless / hydro, i'd also recommend 60 ppm P or more throughout @ 6,0 ish and 1,4ec or so overall. Rising tide and such...


Thank you