How to deal with root rot in cannabis plants

How to deal with root rot in cannabis plants
Steven Voser

Root rot is a difficult fungal disease to treat, and it can devastate a cannabis crop. Be sure to look out for the symptoms of this condition, and carry out the necessary preventative measures to keep your plants safe.

Growing cannabis is thoroughly enjoyable and highly rewarding, but comes along with various challenges. Growers need to constantly be on the lookout for invasive pests and the onset of disease, as these factors can damage plants and result in an overall decrease in yields. One such disease is known as root rot.


Root rot is a condition that can affect both indoor and outdoor plants, and often results from poor soil drainage. The disease can be inflicted by various species of fungi such as Fusarium, Pythium, and Rhizoctonia.

These fungi especially target seeds and seedlings, meaning your youngsters are the most vulnerable to an attack.

Root rot fungi develop from spores and can dwell within the topsoil for long periods of time, and may have even been there before you ever planted your crop. The disease can also strike hydroponic plants and survive within hydroponic reservoirs.


Root rot starts to develop under a set of specific conditions. One environmental factor that can really set it off is dampness. Overwatering soil-grown plants is a definite contributor to the condition. Temperature also plays a large role in the development of root rot, with the fungi flourishing between 20–34ºC. When it comes to hydroponic systems, heat in the reservoir makes it very easy for the fungi to reproduce.

Light leaks within hydroponic systems can also encourage root rot, giving rise to the conditions for unwanted populations. A lack of oxygen can also contribute to its formation. Be sure that your aeration pump is running correctly.

Also, be sure to check your reservoir for any organic matter that may be floating around in there. If this starts to decompose, then root rot may set in.


Symptoms of root rot

Root rot can manifest in many ways, with symptoms occurring in various parts of the plant’s anatomy. The leaves will start to present brown or burnt edges, pale colors, and brown spots. The tips and edges of leaves may start to burn and curl upwards or downwards. Old leaves may die-off, and abnormal or slowed growth may occur.

Overall, plants will start to look generally weak and may wilt or fall over entirely. In hydroponic systems, roots will turn brown and mushy and may give off an unpleasant smell.


Once root rot has set in, it is extremely hard to deal with. The spores of the fungi are tiny and impossible to see without a microscope, making it hard to detect its spread. Basically, if a plant has root rot, it’s a lost cause. Prevention is the best approach a grower can take.

The first port of call is to test the growing medium. Before you start growing plants outdoors, it would be wise to make sure the fungi isn’t present within the soil. Because it can lay dormant within media for a long time, you may be transplanting your herbs right into an infested spot.

Be sure to use soil that has good drainage. If you are growing your plants in pots, perlite can be used to boost aeration. Maintaining healthy amounts of microorganisms in the soil can help to combat root rot. High-quality compost and various products can be used to achieve this.

Pest control is also an important preventative measure to take. Fungus gnats can carry root rot, so repelling them is key. Hitting the watering sweet spot is a good way to keep both fungus gnats and root rot at bay. Make sure the topsoil is dry before watering your plants to prevent overwatering.

If working with a hydroponic system, prioritize cleanliness. Keeping all of your equipment clean will minimize the occurrence of root rot. Adding beneficial bacteria into your reservoir can also help to combat the condition.

If a plant does unfortunately fall victim to root rot, be sure to immediately discard the affected specimen and substrate. What’s most important is that the spores don’t spread to nearby plants and infect the entire grow-op.

Steven Voser
Steven Voser

Steven is a long-time veteran of cannabis journalism, having delved into every aspect of the subject. His particular interests lie in cannabis culture, the emerging science of cannabis, and how it is shaping the legal landscape across the globe.