Mold On Cannabis Plants: All You Need To Know

Mold happens on cannabis in warm and humid growing spaces, it can develop on a plant’s leaves, buds or roots.
06 July 2021
9 min read
Mold On Cannabis Plants: All You Need To Know

  • 1. What is mold?
  • 2. Ideal conditions to prevent mold
  • 3. Mold on cannabis
  • 4. Botrytis
  • 4. a. Identification
  • 4. b. Prevention
  • 4. c. Treatment
  • 5. Powdery mildew
  • 5. a. Identification
  • 5. b. Prevention
  • 5. c. Treatment
  • 6. Root rot
  • 6. a. Identification
  • 6. b. Treatment
  • 7. In conclusion

If you want to have a smooth growth cycle without any headaches, it’s essential you do everything you can to avoid moldy weed. From checking and adjusting the growing conditions to applying fungicides as prevention. Mold can happen during veg, flower, and even after harvest, making buds unsafe to smoke, infecting surrounding plants, and even killing them. So here’s everything you need to know about mold on cannabis plants, from identification to prevention, to treatment.

1. What Is Mold?

Mold is a fungus that grows in multicellular filaments (aka hyphae) and there are several different types of fungi species that grow from hyphae, resulting in a fuzzy appearance, almost always being white but sometimes grey in coloration, which is due to the mycelium (which is the mass that forms from a mass of hyphae). 

The fluffy or dusty texture you often see not only in cannabis plants but in all types of plants and foods is caused by the spores formed at the ends of the hyphae, and these spores are what you see when your plant has been infected with mold.


Mold on cannabis plants: what is mold?

Mold releasing spores.

Dealing with mold on cannabis is a grower's nightmare because the spores are so light that even a light breeze can carry them from one plant to the other, contaminating your whole crop in just a couple of days or hours. As mentioned, mold refers to several fungi species but, when talking about cannabis, there are a couple that you should be aware of, they’re:

Common Types Of Mold In Cannabis

Known asScientific nameAffects
Bud RotBotrytis cinereaBuds
Root RotFusarium oxysporumRoots
Powdery MildewGolovinomyces orontii Leaves


There are several ways to treat and prevent these types of mold but the best way is to maintain good growing conditions. These conditions will vary according to the stage your plant is in, this is why it’s highly recommended to have a thermo hygrometer to keep an eye on the humidity levels and temperature. So, what conditions should you keep to avoid mold?

2. Ideal Conditions To Prevent Mold

Checking and adjusting the growing conditions is the best way to prevent mold in your grow space, this may be hard to do without the right equipment. If you don’t have the equipment needed, there’s no need to worry, as long as your growing conditions are as close as possible to 20-24°C and 55-60% relative humidity, there shouldn’t be a problem. Now, growing outside of the ranges mentioned doesn’t mean that your plants will get mold but it’s a guideline to know where the growing conditions should be, approximately.

Apart from the growing conditions, here are a couple of tips that will help you achieve the ideal growing conditions.

Tips To Prevent Mold Indoors

  • Oscillating fans help circulate the air, preventing air from becoming stagnant and reducing the chances of mold spores landing on your plants.
  • If you’re having trouble maintaining the humidity levels within range, make sure you buy a dehumidifier!
  • Keep your grow room clean! Cleaning up dead leaves and other waste reduces the possibility of fungi growing around your plants.
  • Having an exhaust fan allows air exchange, removing mold spores if there are any.

Tips To Prevent Mold Outdoors

  • A greenhouse provides an enclosed environment, giving you the ability to control the growing conditions with fans and heaters.
  • Grow strains with high resistance to pests and mold, this will allow you to identify and deal with mold before it’s too late.
  • Grow in pots because this allows you to move the plants around if you’re expecting bad weather.
  • If you’re growing directly in the ground, cover your plants with a plastic sheet to protect them from heavy rain.
  • Mold loves humid conditions so place your plants where they get as much sunlight as possible.

3. Mold On Cannabis

It is possible to get mold at any stage of the growing cycle, even in the drying and curing process. This is because fungi need a specific condition to develop. Mold is a fungus that can affect cannabis plants when they’re kept in humid and warm conditions. It can be treated with fungicides or other homemade remedies and can be prevented by controlling the environment but because it rots the leaves, roots, or buds it can be untreatable or very hard to treat.

Also, mold produces spores (and there’s a good amount of spores in the air anywhere you go). Mold spores can stick on your clothes and can be brought into your growing room. They need only humidity and a slightly warmer condition to start developing. We recommend keeping a clean growing environment, even if you never got mold or fungi, it is a great way to prevent it. 

4. Botrytis

Botrytis (also known as bud rot or grey mold) is a type of fungus that affects plants in general. In cannabis, it develops inside the buds and slowly starts to grow outwards, making it difficult to spot in the early stages. So if you were wondering what does mold look line on weed, here's an example.


Mold on cannabis plants: botrytis

Botrytis on Cannabis plant.

Bud rot is easier to get when growing outdoors but can affect indoor growers if the temperature and humidity are not controlled. It can also happen when drying and when curing. If the buds haven’t dried properly they can still hold water, increasing the humidity in the curing jar and ultimately developing mold.


If you can’t see signs of mold but you notice the leaves drying or if you think the buds are not growing properly it can be a fungus starting to develop in your buds. 


Mold on cannabis plants: botrytis identification

It’s really hard to detect bud rot in the early stages because the fungus starts infecting your plant from the inside out.

If you spot any of these symptoms, you should try to take a look inside the buds. The inside of the buds should be the same color as the outside, if you see brown or grey spots, it will most likely be bud rot.


This kind of fungus develops in humid and warm places, to avoid this, it’s crucial to have a good growing space. This means you need to provide good airflow, adjust the humidity level for each growth stage, avoid aggressive temperature changes, and keep your growing space clean.


Mold on cannabis plants: ideal conditions

Optimal conditions to prevent bud rot.

For your drying room, in order to prevent bud rot, it is recommended to have a relative humidity of 60% and a temperature of around 20-25°C. This can be achieved not only by controlling the environment but also by pruning or performing LST techniques to keep the branches spaced. By having these elements on point, you can guarantee a healthy plant all throughout the growing cycle.


If your buds are heavily affected you can still treat them, although you should know that this is a way of allowing the plant to finish the growing cycle and it will not get rid of bud rot. The general recommendation is to dispose of the moldy plant to avoid contaminating the other plants in your grow room.

If you still want to save the infected plant, you should start by decreasing the humidity level and temperature, this will cause the mold to grow slowly. After doing this, you’ll need to spray the affected buds with a mold spray. If you see the mold continue to grow, your buds will get mushy and completely gray. At this point, you should remove the buds and if it’s really bad you should consider removing it from the growing space or disposing of it.


Have in mind that the affected buds can be toxic and should not be smoked!

5. Powdery Mildew

Powdery mildew is a kind of fungus that develops on top of the leaves at first. It may look like trichomes to the new growers but it will continue to spread all over your plant.

This fungus is a white powder that can completely cover your plant, especially the leaves, not allowing your plant to perform photosynthesis and ultimately dying it from the lack of energy.

Just like bud rot, powdery mildew produces spores that can easily spread indoors and outdoors and need very specific conditions to develop.   


When powdery mildew first starts growing, it can be hard to spot it. You may see small bumps on the leaves, but because they are so subtle, you’ll most likely know you got powdery mildew when white powder starts appearing on your leaves.


Mold on cannabis plants: powdery mildew identification

Powdery Mildew on a Cannabis plant.

The white powder will start covering the leaves until they’re unable to absorb light, if it gets to this point, the leaves will wrinkle up, start yellowing, brown, and die. Powdery mildew starts growing slowly but it can completely take over your plant real fast, so if you fail to spot it before, be sure to take action as soon as you see the leaves starting to be covered by a white powder.


As said above, fungi grow in very specific conditions, so the best way to prevent it is to maintain a good growing environment. This combined with minimal pruning or LST techniques will effectively prevent it. Growers who foliar feed should be especially careful, leaving drops of water on top of the leaves can easily cause powdery mildew.


Powdery mildew can be a little bit easier to treat. First of all, you should adjust the temperature and humidity in your growing space, and remove affected plants from it. You should also check the other plants, as spores can easily spread to all the plants around. If your plant’s condition is too grave, you should start by removing the affected leaves and buds, and spray with any fungicide of your choice.

Remember, anything you spray on your plant will affect the smell, flavor, and quality of the buds, so you should opt for organic products or even try making your own at home.


Mix 35ml of apple cider vinegar to 1L of water or mix 400ml with 600ml of milk and spray your plant to treat powdery mildew. Have in mind these methods can fail sometimes and are usually recommended if the fungi infection is in its early stages.

6. Root Rot

Root rot is similar to bud rot, although it happens on the roots. This happens in soil when you get fungus gnats or when you overwater for a long time but it is more common in hydroponic setups.

Root rot is also hard to spot when growing in soil because the roots aren’t visible. Even experienced growers might notice it only when the plant can no longer be saved.


Root rot is easy to identify, as bud rot, you will see the roots start to turn brown and mushyHave in mind that you will only see the roots if you completely remove your plant from the soil.


Mold on cannabis plants: root rot identification

Growers usually check the roots in the last instance and in most cases, it is already too late.

When the roots start rotting, your plant will start showing (what looks like) symptoms of overwatering, deficiencies, curling of leaves, or other symptoms that may confuse you into thinking it is something else. Prevention To prevent this fungus, you should not only keep a good growing environment but also make sure to not overwater your plants, as this can attract bugs like fungus gnats and also drown your roots, causing root rot.


Root rot is something that’s not treated in most cases because it will certainly affect your plants' growth, so when growing in soil most growers will dispose of the plant. It is commonly agreed that a plant with severe root rot is not worth it because the roots will not recover to 100%. If you still want to treat it you can clean the roots with a mix of 5-10ml of baking soda or 10ml of bleach with 1L of water.

7. In Conclusion

It is relatively hard to get a fungus to affect your plants if you are keeping them in a good environment but it's essential you know how to tell if your weed has mold. Maintaining a good environment may seem easy to most growers but can be extremely hard for new growers, especially in countries when it’s hard to find growing equipment.

If you’re tired of your plants getting mold, we recommend trying more resilient strain, like our Gorilla Cookies Auto.

Gorilla Cookies Auto
5 out of 5
I got 134g off this gal growing in 3 gal pot with 24 hours of light. i'm stoked with the result! Smells like diesel. Was a great grow overall.
Verified customer
Reviewed 24 June 2020

We also recommend checking your plants every day and start taking action as soon as you see even the smallest sign that something is wrong. Have in mind that even if you can treat mold, it will affect the final yield and can affect flavor, smell, and effect, so the best thing is to prevent it. 


If you have tips and tricks to prevent mold, feel free to help fellow growers by leaving a comment in the comment section below!



This post was most recently updated on July 6, 2021.

06 July 2021