Root Rot: What It Is & How to Prevent It From Destroying Your Plants

cannabis growing

Have you ever encountered a cannabis plant wilting or exhibiting brown spotted leaves after a normal watering? These could be the signs of root rot. Even the best cannabis growers using the industry's leading techniques and growing procedures experience equipment failures, pests, and other problems like root rot. Knowing how to deal with these issues, however, is the difference between a successful harvest and having to throw your plants into the compost.

What is Root Rot?

disease cannabis plant

Root rot is a plant ailment that can be found in almost any method of marijuana growing. Although it is more common in indoor plants, particularly in hydroponic systems, it can affect both indoor and outdoor plants, grown hydroponically or in soil, especially plants potted in heavy soils with poor drainage.

Root rot can be caused by several different organisms such as certain types of algae, bacteria, fungi, and parasitic oomycotes. A particularly common source of root rot is the water mold Phytophthora, whose spores are not only airborne but can be carried by pests in soil.

Although originating from different sources, growers generally refer to all such cases as root rot because they all share the common effects of turning healthy white/cream-colored roots into a twisted, slimy, brown mass of muck.

The resulting muck denies the cannabis plant adequate oxygen and water, thus choking off the plant's food source. Root rot mostly affects hydroponic systems, but in any situation where cannabis roots are sitting in wet conditions without an oxygen source, they are in danger of developing root rot.

What Are the Symptoms?

Root rot can cause a range of symptoms, because without the root system functioning properly, the plant is essentially shutting down. Often times, symptoms will resemble a plant that has been grossly over or under-watered.

Here are some signs your plant may be suffering from root rot:

  • If plant roots turn brown or slimy, or begin to twist or smell bad
  • Plants appearing to be over-watered; plants wilting or drooping overnight
  • If leaves start turning yellow or white or are falling off quickly
  • If the tips of young roots are turning brown early on
  • Lack of water absorption (plants infected with root rot drink much less water than usual)
  • Root rot can also cause a variety of nutrient deficiencies because the plant cannot effectively absorb nutrients through the roots any more.

What Causes Root Rot?

Root rot can be caused by several organisms, but just as they all have similar symptoms, they all develop under the same basic conditions.

For any cannabis plants grown in any soil-like medium, there is one major condition needed for root rot to manifest itself: stagnant water at the roots. If you are growing your plants hydroponically, particularly in Deep-Water Culture systems (DWC), root rot can be a major problem.

Here are some of the most common factors affecting root rot development:

  • Lack of oxygen; When roots sit in unoxygenated stagnant water, it creates a breeding ground for all the wrong organisms.
  • Light; Any light – sunlight or artificial light – that leaks into your reservoir will promote unwanted algae and fungal growth inside the tank.
  • High Temperature; A warm, nutrient-rich water reservoir makes fungal, bacterial, and algae reproduction much easier.
  • Debris; Any additional organic matter in the reservoir should be removed as soon as possible, as the decay can lead to harmful organism development.
  • Young Root Disruption; Young roots need time to develop a healthy biofilm for defense against invasive organisms. Avoid shocking the roots by handling them or changing DWC reservoir water earlier than you might think is necessary.

Reversing the Rot

Just as root rot can be introduced by many different parasitic organisms, there are many different solutions to the problem as well! There are several common root rot culprits and solutions that are more area-specific, depending on where you're growing your plants. The good news is, though, no matter what pathogen you have, there are two main approaches when fighting root rot:

  1. Directly treat and protect the cannabis plant's roots with an agent specifically for killing root rot.
  2. Change the cannabis plant's root growing environment, thereby removing any ideal root rot conditions.

It is also important to note that, similar to other plant deficiencies and diseases, some cannabis roots infected with root rot may never recover. If you see any new root growth coming out of the previously sick roots that is pearly white, slime-free, untangled, and overall healthy-looking, that is definitely a hopeful sign for your plant.

How to Avoid Root Rot

cannabis grow pots

Below is a list of some recommended steps and procedures to explore in order to prevent root rot from developing or coming back and hopefully permanently getting rid of it:

  • Beneficial Root Bacterial; Adding beneficial bacteria to the water is highly recommended as prevention and treatment for many root-related plant diseases. Most products on the market can be used for both soil and hydroponic grow systems. A few of the more popular ones include Hydroguard, Great White, or Rooters.
  • Amend Soil for Drainage; This only applies to soil growers. Add an aerating aggregate, such as perlite, to the bottom of a pot or mix it into your soil to trap oxygen for root absorption.
  • Air Supply/Bubbles; If you are planning on growing in soil, make sure that your mix has sufficient drainage to allow the roots to access oxygen. If you are growing hydroponically, it is tremendously beneficial to dissolve as much oxygen into your water as possible. Make sure to use an air pump and air stone that is big enough to feed your plants and try to find black, light-proof tubing.
  • No Light Leaks; The fact that cannabis roots don't like the light should be reason enough for this to be a priority of any grower. In the case of root rot, though, many of the harmful organisms cause it thrive in the light and heat provided from a light source.

This is especially important for DWC hydroponic growers; you want your water reservoir to be pitch black and light proof. No amount of Hydroguard or Great White can reverse the damaging effects of a light leak in a DWC system.

  • Keep It Cool; Lowering the grow space temperature will also lower the temperature of the water reservoir. Strive to stay under 80 degrees Fahrenheit. Additionally, as the reservoir water temperature rises, its capacity to hold the dissolved oxygen your cannabis plants need drops significantly.
  • Avoid Distressing the Roots; This is a primary focus for the vulnerable roots of any young plants. Moving, jostling, checking, handling, and transplanting young roots can damage fragile root hairs, which stunts potential growth and reduces natural defenses to root rot.

If you are growing using a Deep-Water Culture system and routinely struggle with root rot, it is recommended to hold off on a full reservoir change for the first three to four weeks of your plant's life, or until the roots have grown and developed a healthy layer of biofilm.

  • Keep Equipment Clean and Sterile; This is an excellent rule of thumb to follow regardless of how you are growing your plants. If you are growing in a hydroponic system, make sure to sterilize all your equipment to kill any lingering fungus or bacteria. You should also be sure to keep your reservoir water free of dead roots and other debris to avoid providing a food source for any dangerous organisms.

If you are using soil-filled pots to grow, make sure to clean and dry any excess water left in the drain pans after watering. Pots sitting in stagnant nutrient filled water can be a breeding ground for harmful bacteria and fungus.

You now have all the information you need to prevent and get rid of any root rot that might be hampering your plants. You should now be much better equipped to keep your cannabis roots and plants healthy for successful grows in the future!