Is It Time to Say Goodbye to Your Cannabis Fan Leaves?

By Cory Hughes
Published: November 26, 2018 | Last updated: December 8, 2021 06:32:28
Key Takeaways

​Dense canopies can cause a variety of problems in your growroom. By taking the time to get hands-on with your plants and removing excess fan leaves, you can save yourself a ton of heat and moisture related problems.

By far, one of the most overlooked practices in maintaining a pest and mildew free environment for your cannabis plants is the manual removal of fan leaves.


Removing excess fan leaves and creating airflow to the central, denser areas of your canopy is essential in maximizing yields.

Balancing your temperature and humidity is a good start, but it’s not enough to produce the end results you are looking for. You need proper ventilation and air circulation in order to optimize your plants’ ability to take in the rich atmosphere around them.


Sometimes, however, due to the density of your canopy, airflow can become restricted, despite having a good HVAC and ventilation system.

Cannabis plants infected with powdery mildewCannabis grow infected with powdery mildew. - Credit: GreenBox Grown

If your plants are in late stage and looking great, but you find pockets of powdery mildew when you dig into the dense canopy, manual removal could have probably saved you some heartache. Powdery mildew is a fungal disease that at a glance looks like baking flour dusted on your plants. It thrives in warm, moist conditions.


(Read also: Managing Cannabis Fan Leaves)

Sometimes this “dust” can be ejected from the plant, resulting in a small puff. Gross. The manual removal of fan leaves located deep in your canopy opens tunnels through which fresh air can flow. Why do you need tunnels of air? Opening up your canopy keeps temperatures cool in those deep, dark places.


When the density of your canopy reaches a certain point, temperatures and humidity can rise. The fresh, cool air from your HVAC just can’t efficiently reach the central dense areas.

Having pockets of warmer, moist air doesn’t always lead to problems with powdery mildew. If the spores aren’t there, then they just aren’t there, but to not find powdery mildew, and to some degree mites, in a home or commercial grow, is rare.

Cannabis plant infested with spider mites Cannabis plant infested with spider mites - Pong Pong/Shutterstock

Another problem that may arise is an infestation of spider mites. Spider mites, much like powdery mildew, love warm, humid conditions. These are pests that are hard to completely remove. As a friend of mine once put it, it’s about integrated pest management, not integrated pest eradication.

(Read also: Integrated Pest Management (IPM) for Small-scale Growers)

The time you really want to watch for dense pockets of fan leaves is in the mid to late stages. In early stages, density is not a problem. Plus, in early stages you want your plants to grow up and out, using as many fan leaves as possible to suck up energy from your lights.

Now, this might be obvious, but I have to say it anyway: if you are not concerned with maximizing weight through plant count, and are growing for more aficionado purposes, then odds are you are not going to have many of the same problems with your canopy.

The only manual removal that should probably have been done in this instance is your basic bottom pruning. But if weight is your goal, plant count will get you there, and manual removal is your friend.

Here is my strategy for manual fan removal: I like to imagine a point deep in the canopy—one I obviously cannot see. From there it is as simple as removing the fan leaves that are blocking my view.

Cannabis fan leaf removed from the canopyCannabis fan leaf removed from the canopy. - Cascade Creatives/ShutterstockWalk along the side of your tray or growing space and look between each cola. If you can’t see into the heart of the canopy, feel free to start plucking leaves, but be careful not to remove the precious sugar leaves that circle your colas.

Those tiny crystalline beauties can go on to make extractions, so you might want to leave them. At first you should only be concerned about removing the large fan leaves that are obstructing airflow to the core of your canopy, and then approach the removal process from different angles.

Stand above your plants and look down. Are there any colas being blocked from the light by excess fan leaves? They should be removed to not only open airflow, but to clear paths of light to areas that may have fallen into the shadows.

Grower removing fan leaf from flowering cannabis plant.Removing fan leaf from flowering cannabis plant. - OpenRangeStock/Shutterstock

If you have to manually remove powdery mildew-covered leaves, it won’t entirely remove the problem, but it’s a start. You are really only removing the leaves to prevent the mildew from spreading further.

At this point, you really should have tackled the problem sooner. Not much consolation, I know, but I’m here to help you prevent these problems in the future. Monitoring your canopy and tackling fan leaf removal early enough will save you a headache later on.

Growing cannabis is one heck of a balancing act. The manual removal of fan leaves to control pockets of humidity and prevent fungal infections is just one part of a larger pest management program.

Keeping away the critters and the mildews may seem challenging, but putting to use best practices of an integrated pest management system works. Manual fan removal is one of the easiest and best ways to boost the health of your plants.

(Read next: 10 Common Marijuana Leaf Problems and How to Fix Them)


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Written by Cory Hughes | Commercial Grower

Profile Picture of Cory Hughes

Cory Hughes is a former police officer turned full-time commercial grower in Denver, Colorado.

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