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Root Rot in Cannabis Plants – How to Solve and Prevent the Problem

Root rot on cannabis can cause some serious issues, in this article we will look at diagnosing the problem and then solving it.

If you’ve been noticing discoloration and wilting of the leaves on your cannabis lately, consider that it may not simply be a lighting or nutrient issue. Many variables might lead to root rot in marijuana, ranging from temperature issues to light leaks.

Poor soil drainage or even specific fungi or bacteria may also be to blame. Read on for advice on how to diagnose and treat this condition and get your plants back on track to produce some beautiful buds.

What Is Root Rot?

Especially common in hydroponic systems, root rot is a blanket term for any number of issues that may be present below the surface. This should be considered a severe threat to your plants as root rot in cannabis tends to kill off the plant if left untreated.

Cannabis Root Rot Symptoms

As with any ailment, the key to effective treatment begins with an accurate diagnosis. Here are some of the cannabis root rot symptoms that should draw your attention when caring for your plants.

Curling Leaves

Extreme temperature variance often gets blamed for curling or cupped leaves; this may also be a sign of overwatering or poor soil drainage. Curling leaves are a very early indication of a plant in distress and warrant investigation.

Brown Spots on Leaves

Commonly associated with calcium deficiency, brown spots may also be an indicator that your plant is struggling to absorb nutrients through its roots. If you haven’t changed lighting systems or mineral levels lately, ensure you take a look at the roots’ condition.

Brown Slimy Roots

Brown roots may be a clear sign of an unhealthy taproot system, especially if a stench or an oily film accompanies it. These signs indicate a fungal or bacterial infection that you should treat as soon as possible.

Cannabis brown roots slimy
Photograph by Scot Nelson

You’ll want to stop your hydroponic system altogether, as any circulating water will potentially spread any contaminants. In cases like these, it would be best to remove the directly affected plants. Remember to treat the remaining ones and do a complete water change and equipment sterilization.


Wilting leaves are often associated with cold shock. Maintaining a comfortable and constant temperature for your cannabis plant will go a long way in preventing root rot in cannabis. For those of you growing indoor weed, this should not be a problem. If you see this in your outdoor plants, consider moving them to a warmer, sunnier area.

Slow Growth

Weed is called such for an excellent reason. Most varieties grow at a reasonably fast pace, with some autoflower strains reaching full maturity within four months.

If your plant is having root problems, it won’t take in the water and nutrients needed to grow at a reasonable pace. You should investigate further if your plant stays the same size for weeks on end.

What Causes Root Rot?

Now that you have a good idea of the early warning signs let’s look at some of the most common causes of root rot in cannabis plants.

Temperature Too High or Too Low

Working on the Goldilocks principle, setting your temperatures “just right,” and maintaining them goes a long way in the health of your plants’ root systems. If you live in warmer climates and you’re growing indoors, you may need to invest in an extraction system or, in extreme cases, an air conditioner.

Keep in mind that your plants will benefit from warmer temperatures by day and cooler ones by night. Humidity is also an essential factor in plant health and should be maintained accordingly. Always try to think about what the plants would experience in nature to best mimic those conditions.

Poor Drainage

All cannabis plants need to take in oxygen through their roots, and poorly draining soil may be smothering them. If it’s too loamy or if you’ve packed it down too tightly, you may cause the roots to become waterlogged.

Think of stagnating water as the enemy; whether it’s in earth or hydroponics, you never want the liquid to remain static for long.

Container Too Small

As with soil that doesn’t drain well, if your container isn’t big enough to accommodate your plant’s ever-expanding root system, it will begin to overwhelm itself. Make sure that you provide the required space for each stage of your plant’s life cycle.

It’s also better to replant into larger containers as it grows, rather than causing problems by throwing your marijuana seedling in the biggest pot you have. Many newbies make this mistake and end up over or under watering, causing the soil to compact or the roots to dry out.


You should only water your plants when they need it. Overwatering is easily the most common cause of root rot in cannabis, and it also dilutes the nutrients present in the soil. Once your plant is close to maturity, you want to water-cycle the earth.

That is to say that you should water once and then wait a few days until the top of the mix is nearly dry before wetting again. This method promotes healthy root growth and makes sure you’ll never have to deal with rotting taproots due to waterlogging.

Soil Too Dense

If your soil is packed too tightly or has a high volume of clay present, the taproots may soon find themselves oxygen-starved, which will give marijuana root rot just the kind of foothold it needs.

Healthy cannabis roots
Healthy cannabis roots

If you’ve opted to use quality pre-mixed soil, you shouldn’t have this problem. You can add peat, coconut fiber, or even sand to loosen your dirt and allow oxygenation. Loosely packed earth is essential in preventing cannabis root rot in the soil.

Lack of Oxygen

Oxygen plays a massive role in the overall health of your plant, as well as its root system. We’ve already looked at ways of improving oxygenation in your soil. DWC root rot is especially common. If you have a hydroponic setup, make sure that you provide ample oxygenation through the use of air pumps and air stones in all of your containers.

Light Leaks

In a DWC system, you want to keep your growing medium in the dark or, ideally, a blacked-out enclosure. UV-blocking water containers and plumbing will prevent the formation of algae and other potentially harmful bacteria.

Above ground, consistency is once again key. Much like us, cannabis plants need a healthy light cycle to be happy. Your indoor setup needs to allow for at least a few hours of complete darkness during the course of each day.


Poor water circulation and under-oxygenation are the leading causes of root rot in DWC systems. Another cause may be pests or contaminants in the water; ensure all your tools and water are cleaned thoroughly before use.

One of the perks of a hydroponics system is that you can spot root rot quickly, as you’re able to see your plant’s roots at a glance. You should consider including this as part of your weekly routine from the time of setup.

Having a good idea of what healthy roots should look like will equip you to spot any problems and fix root rot in hydroponics. Vigilance will empower you to cure root rot in your DWC system quickly.

How to Solve Root Rot

We’ve already established that several variables may cause root rot. For this reason, there’s no single “catch-all” solution. Here are some good practices that will minimize the chances of root rot taking hold.

Add Beneficial Bacteria

Not all bacteria are damaging, and healthy soil contains microbes beneficial to your cannabis crop. There is a wide range of supplemental products available that serve this purpose. If you’re using a hydroponic system, you’ll want to invest in proper minerals to ensure the healthiest of plants.

Pest Control

It should go without saying that a plant that’s stressed out because of mites, aphids, or whitefly is at risk of developing root rot in cannabis. Neem oil is a staple for this reason as it’s an excellent organic form of pest control.

Fresh aloe vera also helps to boost the plant’s immunity and helps to feed it. You can make a basic solution containing these ingredients and apply it from a spray bottle.

Amend Your Water With Oxygen

In hydroponic systems, you need a good quality circulating pump to keep the nutrients moving and the water from stagnating. You also need an air pump with an airstone or diffuser in each container.

Ensure All Equipment Is Regularly Cleaned

Good practice dictates that all of your equipment is kept clean and ready for use. If you’ve experienced weed root rot causing bacteria, make sure all the containers and tools used are cleaned with bleach and left to dry completely. Likewise, always make sure your pruning scissors are sterilized before any cutting to prevent potential cross-contamination.

Ensure Cannabis Root Rot Is Not a Problem!

By paying close attention to your plants and doing daily checks, you’ll be able to quickly spot the warning signs of a potential root rot case.

Cannabis root system healthy

Quite often, if you catch it early enough and treat it accordingly, you’ll be able to turn things around with minimal impact on your yields. Cannabis root problems don’t need to be the end of your crop.

Do keep in mind that even if it’s an entirely unsalvageable cannabis root system, you’ll still be able to take cuttings and propagate them. What remains essential is that you learn from your experience and take it forward to improve future crops.


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