Hydroponic Root Rot (Roots Turning Brown)


Hydroponic gardening is gaining in popularity, but novice members of the hydroponic community may panic and wonder what to do when they see plant roots turning brown.

The leading cause of hydroponic roots turning brown is root rot, and this guide will explain how to detect it, why it happens, and ways to prevent it before it kills all your plants.

Losing a hydroponic crop to root rot is preventable, so stay here to learn the best way to maintain a healthy hydroponic garden!

What Causes Root Rot In Hydroponics?

Root rot in hydroponics happens when fungus, bacteria, and algae start to grow in the water supply. Typically this occurs when the nutrient solution becomes unbalanced.

The fungus Phytophthora is a genus of water-borne molds with over 170 species identified by scientists. This fungus is the main culprit that turns plant roots brown in hydroponic gardening and destroys soil-grown crops with potato blight and other plant diseases.

The pathogen attaches to the plant when fungal-contaminated water passes the roots. As the mold reproduces, it becomes slimy and covers the roots, choking off the plant’s ability to absorb nutrients.

As the plant becomes weaker from lack of food, more of the roots turn brown until it eventually dies.

Root rot develops from pathogens in the water/nutrient supply because conditions like warm water temperature and low oxygen or pH levels allow the Phytophthora to flourish as it recycles through your hydroponic system.

Will Root Rot Go Away On Its Own?

Not only will root rot never go away on its own, but it can quickly move to other plants sharing the same nutrient solution inside a hydroponic planter.

Problems with root rot are most prevalent when using the Kratky Method or Deep Water Culture (DWC) hydroponic systems that don’t always allow roots contact with the air or the nutrient solution to be properly aerated.

To fix your hydroponic system when you spot plants with root rot, you’ll need to follow these steps:

  1. Turn off the flow of nutrient solution
  2. Inspect all plants and remove dead or diseased specimens
  3. Wash healthy plants in clean running water for several minutes
  4. For plants with minimal root damage, clip off bad roots and wash the plant
  5. Drain the nutrient solution and rinse the system
  6. Turn on the system and add a new nutrient solution
  7. Set thermometer to 70°F
  8. Run air pump for three or four days

It’s smart to remove plants showing a lot of root rot, even if you still see viable roots. You don’t want to chance not properly clearing off the fungus and reintroducing it to your hydroponic system.

What Does Root Rot Look Like?

Root rot detection requires looking at root color and feeling and smelling them. However, you may spot signs on plant foliage first, such as yellow or curling leaves, stunted development, or wilting that will indicate you need to inspect below the water line.

healthy hydroponic roots

Healthy plant roots are usually white or cream with a firm texture, but it’s common for the nutrient solution to turn them into a tan, brown, or rusty shade.

Plants with root rot from Phytophthora will have a tan or brown color, and affected roots will feel slimy and mushy to the touch.

Plants can also have root rot from brown slime algae (cyanobacteria). So if you see slime rapidly multiplying on plant roots and it changes color from clear to thick yellow mucus, brown slime algae are the pathogen you’ll need to treat.

How Fast Does Root Rot Happen?

Root rot can kill plants in as fast as seven to ten days once the pathogens take over.

This timeframe means you must keep a keen eye out for plants that show distress, so you can remove the ones that have root rot and hopefully save the rest of your crop.

In a soil-based garden, you can often fix root rot by allowing the planting soil to dry out. However, in a hydroponic system (especially a DWC), plant roots must continually stay moist, so drying out the roots is not a workable solution.

The onset of root rot is more common in younger plants, especially right after you change the nutrient solution in the planter.

This is because young plants have a delicate root system susceptible to pathogens, whereas established plants develop a biofilm of protective bacteria on their roots that can thwart root rot.

What Does Root Rot Smell Like?

Healthy hydroponic plant roots should have a slight earthy scent that is pleasant.

However, when root rot sets in, you should expect the plants to emit a strong odor of decayed plant matter or mildew.

As the rot becomes more extensive, the aroma moves toward a sulfur-like stench of rotten eggs or takes on the odor of sewage.

How To Prevent Root Rot In Hydroponics

Whenever you use a water-based system to grow plants, the nutrient solution must always have the correct pH and oxygen levels to deter pathogens or algae from blooming.

You must also keep the temperature of the solution cool and follow strict sanitation and maintenance practices to keep root rot at bay.

Oxygen Levels In The Nutrient Solution

Keeping your nutrient solution aerated with enough oxygen in the water is critical for maintaining a healthy hydroponic system. You can add more hoses and air stones to the planter to properly oxygenate the solution to help prevent root rot from developing.

pH Level Of Nutrient Solution

You should test the nutrient solution pH daily to have a record of average readings. A good pH range for hydroponic plants is between 6.0-6.5 at the root level.

measuring ph hydroponic system

If you see pH levels drop quickly, it’s a sign that root rot pathogens could be taking over. Most gardeners see root rot when the pH level in their system is in the 3.0-5.0 range.

Use the appropriate acid or base amendments to your nutrient solution to keep the pH level in the ideal range to deter the development of root rot in your system.

Nutrient Solution Temperature Control

Cool temperatures inhibit the growth of pathogens in both the air and water, so keeping your nutrient solution around 70°F is ideal, but anything under 75°F is sufficient.

Most people use a hydroponic chiller to maintain a cool supply of water to their plants, so invest in one if root rot from warm water temps is a problem in your system.

Sanitation And Maintenance

To stop pathogens from getting into your nutrient solution and harming your plants, you should always follow these practices:

  • Remove or filter out any dead plant matter
  • Trim dying foliage from plants
  • Eradicate flies or gnats from the hydroponic room
  • Inspect and clip unhealthy or too long roots
  • Add beneficial bacteria to the nutrient solution
  • Always wash hands and sterilize tools before working with the plants or hydroponic components

In Summary

If you see the roots of your hydroponic plants turning brown, feel slippery, and have an odor, then you’ll need to follow the guide above on how to fix root rot on hydroponic plants and prevent it from returning in new crops.

Growing plants hydroponically takes time to master, but with experience and knowledge, you’ll be on your way to success!

Share This Article