Root Rot

Cannabis Root Rot – Slimy, brown, twisted or unhealthy roots are caused by unwanted pathogens in your hydroponic tank!

The marijuana plant on the left is healthy, and the plant on the right has root rot. The curled, drooping, unhealthy leaves are the result of the plant not being able to get enough oxygen through the roots. Root rot symptoms often look like a soil plant that has been severely over or under-watered.

Example of the effects of root rot on a cannabis plant

Straight to the Solutions for Root Rot!

An example of what cannabis root rot can look like ‘under the hood’. Every infection looks a little different, but brown roots are usually the main symptom. It may affect all or just parts of the roots, and the sick sections usually become slimy or mushy and start twisting together.

These cannabis roots are brown with root rot - they're slimy, smelly, and will kill your plant if not treated immediately!

Healthy Cannabis Roots Are White or Cream Colored!

Example of white, healthy cannabis roots

Root rot can be caused by several different organisms including types of bacteria, fungi, algae and parasitic oomycotes. Although the symptoms are similar between different types, they don’t always look exactly the same.
However, growers generally refer to all types of unhealthy root browning as just ‘root rot’.

Root Rot causes droopiness and other symptoms similar to over or under-watering

Cannabis plant in an Aerogarden with root rot (DWC / Hydroponics)
Example of DWC (hydro) root rot on a cannabis plant in an Aerogarden

The Most Common Triggers for Root Rot Are Light Leaks, Heat & Lack of Oxygen in the Water

Because cannabis root rot can be caused by different pathogens, a solution that solves the symptoms of root rot for one grower may not necessarily work for another grower. What’s attacking your roots in California might be completely different from what’s attacking the roots of a grower in Australia. That being said, there are tools to fight against root rot no matter what kind you have!

The brown tinge on these young roots is the first sign of root rot.

Example of the roots of a hydroponic marijuana plant with the first sign of root rot

Some varieties of root rot mostly affect the roots below the surface of the water while the roots located above the waterline stay white and healthy. This phenomenon is part of why it’s often recommended that hydro growers maintain at least a small amount of air gap under the net pots. Oxygen-rich moist environments (including that misty air gap) make it very difficult for root pathogens to grow.

Sometimes even the roots above the waterline appear brown. The white strands you see in this picture are actually new roots coming out of the old unhealthy stuff. When new white roots are growing, it’s a sign the plant may be getting better! Even after roots have recovered, you may see the brown for a while until it’s completely covered by new white roots again.

Brown, infected roots often appear twisted

The twisting/bunching together is the result of infection. Healthy roots have individual ‘strands’ that tend to stay separated even when they’re all floating together in a reservoir.

Example of twisted brown roots that are the result of cannabis root rot

A mass of root rot. The grower believes that the water level in the reservoir was too high

Root rot on this cannabis plant was caused by the water level being too high

Cannabis roots with root rot sometimes look mushy or slimy and can almost look like they’re covered in snot

Slimy, snotty cannabis roots with a bad case of root rot and possibly an algae bloom

This case of root rot was caused by a brown algae bloom. Brown or green algae is especially common in hot temperatures or when there are light leaks!

Important: The Following Roots Are Stained from Nutrients – They Are NOT Brown from Root Rot

Cannabis plant - roots are brown because they're stained from nutrients, not because of root rot!

Nutrient-stained roots are not slimy or smelly and all the roots are evenly dyed the same color. You’ll be able to see each individual ‘strand’ on healthy cannabis roots, as they won’t be twisted together. You also won’t see leaf symptoms or wilting on the plant itself.

The first sign of root rot is usually wilting or drooping, though sometimes you won’t have any symptoms at first. Root rot often strikes immediately after disturbing the roots or completing a reservoir change, especially with young plants. It’s a good idea to avoid disturbing young seedling roots when possible! This gives roots time to build up a biofilm that protects them against root rot.

This cannabis plant was completely healthy the day before, but started looking weak after being transferred from one hydroponic reservoir to a different one. The thin, light colored plastic of the reservoir may have been letting light through, making the reservoir a haven for root rot. Additionally, the temperature was about 85°F (30°C) in the grow space!

Example of the clawing, curling leaves caused by cannabis root rot (root problems)

Cannabis root rot can cause leaf symptoms that can look like almost anything: cannabis leaves get burnt edges or tips; yellow / bronze / brown spots or stripes; nutrient deficiencies; clawing and curled edges; and other unusual leaf symptoms.

Curling and other typical signs of root problems are often present

Example of curling leaves from root rot on a marijuana seedling in a hydroponic / DWC setup

Root rot can cause curling leaves and brown or burnt patches

Sometimes you’ll have a plant with root rot that looks completely healthy other than the roots. Don’t ignore this problem as you will likely start getting symptoms!

What Causes Root Rot in the First Place?

The plant ailment we think of as ‘Root Rot’ is actually a bunch of similar symptoms caused by many different types of organisms. Since these organisms all cause thesame problem ‘gross, brown roots’ we group them together. In addition to these harmful organisms all causing similar symptoms, they also show up for the same reasons.

So what causes root rot? If you’re growing in soil or coco coir, there’s one main cause: stagnant water at the roots. If your plants are sitting in old water that’s getting light (from the sun or otherwise), their roots are connected to a breeding ground for unwelcome organisms.

These cannabis roots are brown with root rot. Sick roots often look wound up or twisted like this, and the individual "strands" sort of meld together with slime

Root rot is a major problem to look out for in DWC many factors can cause it to show up. The most common are:

  • Heat: A warm reservoir makes it easier for bacteria to reproduce. In fact, keeping a cool reservoir makes for an environment in which harmful bacteria/fungi/etc. just can’t survive.
  • Light leaks: Light in your reservoir equates to a population boom for some of the smaller, unwanted populations living.
  • Lack of oxygen in the water: When you remove the air and agitation from your reservoir water, it’s party time! A gross, smelly, sad party.
  • Agitating young roots: Young roots need time to build up their defenses. Moving them not only weakens them, but it potentially exposes them to new pathogens.
  • Decaying matter in the reservoir: Old bits of dead leaves can be the start of something bad. Make sure you fish any plant matter out of your reservoir when you see it. Except for your roots leave those in there.

Your cannabis plant has started drooping, leaves are getting sick, and roots are brown, twisted, smelly and/or slimy. These are all signs you have cannabis root rot

The first sign of root rot in hydro cannabis plants (besides brown roots) is usually wilting

When a plant is wilting or drooping, whether it is in soil, coco or hydro, it is almost always a sign that’s something is going on at the roots.

The wilting is often soon followed by other symptoms to the leaves, especially burning, brown spots, nutrient deficiencies, spotting, and other unusual leaf symptoms.

Root rot can cause a wide range of symptoms, because without the roots the plant is shutting down!

This is an example of what cannabis leaves can look like after the plant starts suffering from cannabis root rot

Plants with root rot often start drinking less water. If you notice symptoms in your cannabis plant, make sure to take precautions to stop root rot from getting worse!

A cannabis plant affected by root rot - leaves are turning brown, discolored, burnt white tips and edges, curling
A cannabis plant affected by root rot - leaves have spots, burnt yellow tips and edges, curling

Some brown roots may eventually turn white again after the root rot is gone, but it’s important to note that damage is permanent on the leaves. Brown leaves will never turn green again. You need to watch the roots and the new leaf growth for signs of root rot recovery.

Root rot mostly affects marijuana plants in hydroponic systems, but roots can also get pathogens as a result of over watering your plants in soil or other medium. Basically, anytime the roots are sitting in wet conditions for too long without any oxygen, they are at risk of developing root rot.

  • Cannabis plants with root rot almost always appear overwatered or droopy (sometimes plants wilt overnight!)
  • Brown, slimy or smelly roots
  • Plant leaves often start turning yellow or white
  • Leaves may start dying and falling off rapidly
  • Oftentimes you’ll see what appears to be a random mix of nutrient deficiencies on the leaves ‘“ this is due to the fact that the plant can’t absorb nutrients properly at the roots even if they’re there
  • Plants may drink much less water than usual
A gross, slimey case of brown roots - caused by a pathogen known as "root rot." Yuck!

Now that you know what root rot looks like and how to get it, it’s time for cannabis root rot solutions!

Solution: What to Do About Marijuana Root Rot, Algae Growth & Slime in the Reservoir

It can be tough to get rid of root rot and many growers feel it’s easier to just scrap the plant and start over. However, if you’re growing in the same spot you’re likely to get it again unless you find a true solution, and there are proven techniques that will cure your plant of root rot problems!

In order to get rid of root rot successfully, you need to take a two-pronged approach. You will need to:

  1. Treat the plant’s root directly with something that will help protect them against root rot
  2. Change the plant’s environment so that root rot no longer has a good place to grow.

Go through the below list and make sure you’re covering all your bases to get rid of root rot permanently and prevent a re-occurrence. It’s also important to note that affected roots will likely never recover, just like how discolored leaves on the plant will never recover. What you’re looking for is new, healthy white root growth coming out of the old sick roots.

Learn how to prevent and treat cannabis root rot

1.) Add Beneficial Root Bacteria – Crucial!

Some people (like me) add beneficial bacteria to their water to help prevent and treat root-related plant diseases and help make nutrients available to the plant. Some of the formulas available are Hydroguard, VooDoo Juice, Great White, and Rooters. Most of these can be used with both hydro and soil grows.


I personally recommend Hydroguard because I’ve used it successfully to treat root rot in hydro, and I’ve also seen it work for many other hydroponic cannabis growers, too! It’s pretty inexpensive, and concentrated enough that a single small bottle can last throughout your grow.

The ‘secret sauce’ in Hydroguard is a specific type of bacteria called Bacillus amyloliquefaciens. It survives in hydroponic reservoirs better than other types of Bacillus bacteria and fights many root ailments including different types of fungi, bacteria, and oomycotes. It not only gets rid of and prevents root rot, but there’s some evidence Bacillus a. may actually help lower salt concentration in the plant tissue itself!

Great White Root Powder

Great White is another root supplement that works by giving your plant roots lots of good stuff to help it be more resistant to root rot. Some growers (myself included) have tried Great White without seeing any root rot recovery. However, other growers have had great results with this supplement!

It all depends on exactly which organism is growing in your tank! What was growing in mine might not be the same as what’s growing in yours, so when it comes to ‘good bacteria’ supplements it can’t hurt to try more than one if the first one doesn’t work.

A small sample of Great White doesn’t cost much, so if you’re still struggling with root rot after trying everything else, it’s worth giving it a try to see if it works for you!

2.) Lots of Bubbles

As I mentioned, it is incredibly beneficial to try to get as much oxygen as possible dissolved in your water. Therefore, it’s a good idea to buy a medium sized air pump and big air stones for your hydroponic system.

Up to a point, the more bubbles and surface agitation, the better, as this dissolves more oxygen into the water. As long as the roots are not being very disturbed, you can’t really go wrong with adding more oxygen.

Root rot cannot thrive in an oxygen-rich environment and your plants will grow faster with lots of oxygen. I use one EcoPlus 2 Air Pump w/ 2 Outlets for each 10 gallon container (which each hold 5 gallons of water), which I have connected to 2 large air stones per air pump since this one has 2 outlets; this helps make sure there’s plenty of oxygen in the water healthy roots and faster growth.

You need 3/16-inch standard aquarium tubing to hook everything together. Try to get tubing in black if possible, to ensure light can’t get through.

This has worked great for me, I haven’t had root rot since I started using this air pump/air stone combination with Hydroguard. But lots of different pumps and types of air stones will work great, the important thing is to make sure that you’re seeing lots of bubbles!

Make sure there are lots of bubbles in your plant reservoir to help protect your cannabis from root rot!

3.) No Light Leaks in the Reservoir!

Your roots don’t like light, which is reason enough, but the bad organisms that attack cannabis roots love the heat and light they receive from your grow lights!

Therefore, hydro growers want it to be completely pitch black in their DWC reservoirs. You should not be able to see even a tiny bit of light where your roots are!

You don’t need to worry as much about repairing light leaks when using a dark, thick and sturdy tub as your water reservoir

In order to accomplish a totally dark reservoir for your marijuana plants, here are some things to keep in mind!

  1. Consider the Material & Thickness of the Reservoir Tub: Darker and thicker material will let less light through to the reservoir.
  2. Consider Reflectivity: Pale colors tend to reflect back more light and heat, but you can always increase the reflectivity later by covering the lid with a reflective material!
  3. Check Thoroughly for Light Leaks! You may need to get down low and look up to see them!
  4. Use Opaque Tape to Cover Any Light Leaks ‘“ Electrical tape and reflective tape are great options for covering up places where light is getting through.
  5. Use Dark (Light-Proof) Tubing: Another way to protect the water from light exposure
  6. Light-Proof Your Net Pots. Neoprene net pot inserts are great to fill in the net pot instead of using clay pebbles, and won’t let any light get through. Other great options include net pot covers.

All the Hydroguard, Great White, H2O2 or other root supplements in the world often won’t solve a root rot problem if there’s a light leak!

4.) Keep Grow Room Cool

Lower the temperature of the grow space under 80°F, and even better under 75°F. This also lowers the temperature of the water in your reservoir. Water can’t hold much dissolved oxygen at higher temperatures and your plants need oxygen to ‘breathe.’

Getting more oxygen to the roots not only helps fight root rot, it makes your plants grow much faster. If it’s too hot in the grow space, you’re much more likely to run into root rot as well as overall droopiness.

In an ideal world, the maximum recommended temperature for the water in your reservoir is around 72°F (22°C) and some growers will go to great lengths to keep their reservoirs very cool. However, when using a great supplement like Hydroguard that fights root pathogens directly, you can often keep the temperature quite a few degrees higher without as a problem.

5.) Avoid Disturbing Roots, Especially Young Plants

When it comes to nutrients and plant growth in a hydroponic setup, it’s important to watch over your roots and change your reservoir water regularly. This is especially important in the flowering stage when the plant is very sensitive to nutrients and pH. Regularly changing your water every 7-10 days will help your plants get better access to nutrients, and help prevent deficiencies and toxicities.

However, when your young seedling or clone is first getting established in your hydroponic system, it doesn’t have an established a colony of good bacteria around the roots, and has not yet grown a biofilm that protects the roots against pathogens.

During this initial period, a full reservoir change can throw everything off balance, and your roots have to sort of ‘start over’ from the beginning.

That’s why if you historically struggle with root rot, it’s recommended for the first 3-4 weeks of your cannabis plant’s life to only top off the reservoir with additional nutrient water, and hold off on a full reservoir change until your plants have grown lots of roots with a healthy layer of biofilm over all the roots and sides/bottoms of the tank.

6.) Keep Everything Extremely Clean & Sterile

In a hydroponic system, make sure that any dead roots, dead leaves or other types of plant debris doesn’t get into the reservoir because they will provide a breeding ground for bad bacteria as they start rotting. If you do notice organic matter in the reservoir, fish it out as soon as possible.

You also want to keep your grow area as clean as possible at all times to stop bacteria before it starts. Before you begin your grow, it’s a great idea to clean all grow-related items to kill any bacteria or fungus.

Hydrogen Peroxide (H2O2) Is Only a Temporary Solution: Use alongside something else for more long-lasting prevention!

Some people recommend treating cannabis root rot with H2O2, also known as hydrogen peroxide. While adding hydrogen peroxide to your water will kill most bacteria and pathogens, including the ones that cause root rot, it is only effective in your system for a day or so or since the H2O2 is quickly converted to oxygen and water.

Therefore, if you use hydrogen peroxide as a treatment for root rot, you will need to treat your water daily to prevent re-occurrences until you actually fix the problem that is causing your root rot in the first place. I have used commercial grade H2O2 against root rot more than once, and I never saw any noticeable difference, so I would NOT RECOMMEND H202 as any type of long term cure!

Why Not Use Hydrogen Peroxide? H2O2 is only temporarily effective at best when it comes to getting rid of root rot. It makes me so sad when people tell growers to use H2O2 (hydrogen peroxide) to kill root rot because I know they will continue to struggle with it. Even the commercial grade stuff just doesn’t work most of the time (and I’ve tried)!

All H2O2 does is cause bubbling near the dead brown roots (or any organic matter), which is why I think people believe it’s helping. In my experience, it doesn’t help the plants themselves (they don’t look any better), and what’s worse, all the H2O2 will be completely gone from the water within 24 hours.

H2O2 kills most of the bacteria in the reservoir, including any good bacteria you’ve added, and does nothing to address the underlying problem. You can’t sterilize away root rot, it attacks people everywhere! Although H2O2 does kill bad organisms, it leaves enough of it there to repopulate your reservoir.

I personally recommend Botanicare Hydroguard the newer, improved version of Botanicare’s popular ‘Aquashield’ root supplement) for marijuana root problems because I’ve used it successfully to get rid of more than once case of Root Rot (and by ‘successful’ I mean new white roots exploded out of the old mushy brown ones and I was able to eventually harvest the buds – look at the pics below).

Hydroguard (and their old supplement Aquashield) are also much cheaper than most other similar root treatments, and in my experience more effective.

Take a look at what happens with the roots from using a supplement like Hydroguard.

What you are looking for is new healthy white roots growing out of the old brown roots. Eventually, as the root ball gets bigger, you will no longer be able to see the old brown roots. After you start noticing a recovery, some growers will snip off old dead roots, but I often don’t.

Canabis plant with root rot - hydroponics - deep water culture DWC

Roots are beginning to recover

Notice the new white roots growing out of the old brown dead ones within just a day or two of receiving Hydroguard in the reservoir. By this point, the plant has stopped showing any new symptoms and appears to be growing normally.

This cannabis plant is beginning to recover from root rot - notice the new white roots growing out of the old sickly brown ones

Roots are now mostly recovered below

Notice that you can barely see any signs of the old brown, and all the new roots generally appear white and healthy. The plants on top are lush, healthy, and fast-growing, though the old burnt leaves never recovered.

Root rot in cannabis - post recovery

In addition to treating root rot, I like to use Hydroguard or as a preventative. It is surprisingly effective even in warm reservoirs. Hydroguard have definitely gotten me through a hot summer before.

Since I first started using Hydroguard in DWC, bubbleponics, and other hydroponics, it has successfully prevented me from getting root rot as long as I keep using it. I also use it when growing in soil if I suspect root problems.

Sometimes it's only the roots above the water that are being affected, and the roots in the water itself are still relatively healthy

Original Article