Root Rot In Your Hydroponic System: 4 Reasons (+ Solutions)

As a hydroponic gardener myself, I can attest that root rot is a major pain. Perhaps, that is the reason why you are here! I’ve struggled for some time until I discovered that the secret to combating root rot lies in removing the conditions required for its development on your hydroponic system.

Root rot in hydroponic systems is caused by 1) wounded plants, 2) oxygen-poor environment, 3) hot nutrient solution and heat, and 4) unclean hydroponic system.

What specific measures can I do to remove root rot in my system? This was the repeating question I had back then. Now, I am enjoying a bountiful harvest and of course, I will not let you finish this article without any gold hacks. Let’s dive in!

Causes of Root Rot in Hydroponic

Root rot emerges because of poor management practices related to oxygen level in the hydroponic system, water temperature, pH, and even sanitation. This causes fungi and oomycetes, the main causes of root rot, to proliferate.

Several studies enumerated specific pathogens causing root rot. Rhizoctonia solani is a fungus infesting tomatoes while Thielaviopsis basicola causes lettuce root rot.

Oomycetes are another group of pathogens that somehow resemble fungi-like growth mechanisms, but they are different in evolution. Phytophthora spp. is an example from this group which affects strawberries, peppers, raspberries, and tomatoes.

Now that we’ve tackled the biological causes, proper cultural management practices is what we need to understand deeper. This will lead us to the question: What exactly does root rot like in a hydroponic system?

1. Wounded Plants

Wounded roots when transplanting increases disease susceptibility. Thus, more chances of being infected with fungi, oomycetes, bacteria, and even viruses.

This factor brings us back to the transplanting process. Remember that any wound in your plant, either in the roots or the plant itself, is a passageway for plant diseases. Wounds can be cuts in the stem, an injury in the roots, or accidentally pinched leaves.

When roots are injured, you provide pathogens with nutrients to eat. They savor these until they invade the whole plant. This is the reason why most root rot symptoms are visible in the upper plant. Some of these are wilting, curling leaves, slow growth, and yellowing of leaves.

2. Low Oxygen Levels

Lack of oxygen is the major cause of hydroponic root rot. A foul odor in the tank and brown slimy roots are common symptoms. These are signs that oxygen is being prevented from going to the plant’s roots.

This is common in passive deep water culture (DWC) and kratky systems wherein roots are submerged in water for a long period. Because the roots are suffocated with stagnant water, oxygen cannot move into the roots which is needed for aerobic respiration—an important process in plants.

This principle holds the common hydroponic question:

Does a small air pump cause root rot?

Air pumps that are too small compared to the size of the hydroponic system will indirectly cause root rot due to the insufficient oxygen level in the tank.

Small air pumps are those that give less bubbles, thus less oxygen. With less oxygen, roots cannot respire sufficiently, therefore leading to root rot.

Imagine using a small fan in a big classroom. Would it provide enough air for everyone? No. The same principle goes with hydroponics. If you have big hydroponic containers, you must choose bigger and stronger water pumps to provide enough oxygen for the roots. Small air pumps must be used for smaller hydroponic systems such as DWC.

Another way to solve this is to add airstones. Airstones create more and finer bubbles, thus increasing the oxygen level in your system. If this solution is still not enough, you may opt to add more water pumps.

3. Heat

A hydroponic nutrient solution above 72°F is one of the main causes of root rot. Hot water and heat create the ideal environment for root-rotting bacteria to thrive.

Temperature plays a vital role in hydroponics. Extreme high or low nutrient solution temperatures affect plant cell membrane integrity and heighten chances of root diseases.

In the case of hotter temperatures, there will be a lower amount of dissolved oxygen (DO) in the solution. And as we tackled a while back, lower oxygen supply leads to root rot. Thus most growers recommend maintaining the dissolved oxygen level at 6 ppm (mg/L).

However, if you are just a hydroponic beginner or someone who gardens for leisure, buying a DO meter is not necessary. This tool would be more applicable for commercial growers. For you, knowing to keep your nutrient water cooler is already sufficient!

4. Unclean System or Tools

Root rot in the hydroponic system can be caused by the use of contaminated hydroponic nutrient, buckets, and even garden apparatus.

Having a consistent cleaning regimen is an effective strategy in hydroponic gardening. Regardless of your hydroponic system, it is essential to keep your tools and containers tidy because they can also be a channel for pathogens.

Active Hydroponic Systems and Root Rot

Root rot can spread in hydroponics. Indeed, in cases of active hydroponic systems, the recirculation nutrient solution provides a faster mechanism for root rot to spread, making the whole hydroponic garden plants affected by the same disease.

This factor now looks at the macro scale of hydroponic gardening. If you noticed, we started discussing a micro factor, which is the plant itself.

Root rot, even pathogens in general, loves a mechanism to fastly reproduce. And in hydroponics, infecting the water is the fastest way to reproduce.

Your nutrient solution is a conduit of the pathogen. Deoxygenated solution leads to root rot. Hot solution gives us root rot. Unclean solution and apparatus result in root rot. All are components of the hydroponic system, right?

Thus at this point, we need to acknowledge that root rot infestation is also a reflection of the system itself. When one part of the system fails to prevent root rot, the whole system suffers.

That is why to end this article, here are the gold hacks I promised. These tips and remedies prevent root rot from infesting your whole hydroponic system!

Gold Hacks to Combat Hydroponic Root Rot

Achieving healthy roots is one of the things every gardener wants. Enumerated below are tried and tested tips to make sure root rot will not thrive in hydroponic systems.

Make Sure Your Hydroponic System Has Lots of Bubbles

Root rot cannot develop in an oxygenated environment, thus having air stones, more and stronger water pumps is essential. It is essential in passive hydroponic systems such as DWC and Kratky, to make sure you do not submerge the roots completely in water.

Having an air space between the roots and nutrient solution will give your plant roots room to breathe.

Have a Cooler Grow Site

A clean hydroponic solution needs to be maintained at 62 to 68°F, 72°F being the highest acceptable temperature.

If you are growing using hydroponic tuna boxes or DWC buckets, painting it white or wrapping it with an insulator can help to lower the temperature. Used clothes are a cheap insulator option.

In commercial production, investing in a water chiller or cooling fans will lessen cases of root rot.

Clean Everything, Yes—Everything

Trowels, buckets, garden gloves, reservoirs, hoses, and net pots should be cleaned consistently every growing season.

Sanitation is key to a successful gardening experience. This includes sweeping and mopping you grow room floors, eradicating dead plants in the system, cleaning filters and hoses, scrubbing your hydroponic water reservoirs, keeping your harvesting area and equipment tidy.

Some agents usually used by hydroponic growers are bleach and food-grade hydrogen peroxide. If you want an organic option, vinegar is also a great sanitizing agent!

This is beneficial to prevent the major causes of diseases in your garden—microorganisms such as fungi and bacteria.

A Beginners Guide: Hydroponic Sanitation & Sterilization

How to Treat Infected Roots?

Trimming the infected part of the root and adding food-grade hydrogen peroxide in the nutrient solution is an effective way to promote root regrowth and health.

If the whole root system exhibits a sign of root rot, do not think twice and dispose of the plant immediately. We have discussed that root rot can affect the whole garden, more especially in hydroponic systems with multiple plants per reservoir.

Meanwhile, for cases with root rot that did not spread that much, you can just cut the infected part off. After this, you will need to replace your nutrient water and mix 2-3 teaspoons of food-grade hydrogen peroxide before putting the plant back in your system.

Hydrogen peroxide disinfects your nutrient solution without any adverse effect on your plants.

Another additive you can add is root builders. These will promote stronger root regrowth as they are high in good bacteria and also help in the aeration in your system.

Further Questions

Why are my hydroponic plants dying?

Plants submerged in water without any oxygen supply are more likely to die. They also need a means and space to breathe. This could be solved by adding an air pump or simply assuring that the whole root system is not completely submerged in water.


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