From cannabis to cantaloupe, hydroponic growers face unique challenges that traditional farmers don’t. If you’re unfamiliar with hydroponics, it’s a method of growing crops without soil or natural sunlight. Plants grow in trays or cups suspended over a water-based nutrient solution, not dirt. The roots grow into the water to absorb oxygen and nutrients.
Hydroponics is a sustainable method of growing food indoors, such as on rooftops, basements, converted buildings, or outdoors in covered greenhouses. It allows growers to control the entire ecosystem, including temperature, nutrients, pH, and light. Hydroponics works in outer space too. The International Space Station crew successfully grew two crops of mixed greens using two hydroponic facilities.
Root rot is the most significant challenge growers face because the roots remain continuously immersed in a nutrient-rich water solution. As we’ll see, it’s not the water but other factors that lead to rotting.
This article will reveal the causes and the best ways to prevent hydroponic root rot. Although there are different hydroponic gardening methods, they all face the same challenge of maintaining healthy plant roots.
Six Types of Hydroponic Systems
There are six fundamental types of hydroponic systems gardeners can choose.
- Deep Water Culture (DWC) – The plants stay suspended over a stationary reservoir with the roots touching the water’s surface.
- Nutrient Film Technique (NFT) – The plants’ roots sit in a constantly flowing stream of nutrient solution. It requires a water pump and a tilted bed so that the water flows back to the reservoir.
- Ebb and Flow system – This system floods the roots and continuously drains the water.
- Wicking system – This system uses a wicking action like a kerosene lamp. The water absorbs into rope or felt where it climbs into the growing medium from a reservoir below the plants.
- Drip system – This type of hydroponics uses water pumps to push the growing solution through tubes where it drips down on top of the individual plants.
- Aeroponics system – Aeroponics sprays water and nutrients directly on the roots as a mist instead of dripping on the leaves.
Most commercial growers use the DWC or NFT systems depending on the crop. Regardless of which method you use, the plant is susceptible to hydroponic root rot.
Why Do Roots Not Rot in Hydroponics Although They Sit In Water?
Most plants will die if their roots stay submerged for prolonged periods, so what makes hydroponics different? There are two reasons, clean water, and oxygen.
A plant’s roots require oxygen. There are microscopic air pockets in the soil, and rainwater contains dissolved oxygen that the roots absorb to survive. Plant roots that sit in stagnant water become starved of oxygen and die.
In hydroponic systems, an aerator adds oxygen to the water simulating the oxygen levels in nature. Aerators, a.k.a. air stones or air diffusers, use pumps that force air through fine pores to help the oxygen dissolve in water.
The other reason roots die if they sit in contaminated water. Pathogens will destroy the roots in nature and an infected hydroponic system.
What Causes Root Rot in Hydroponics?
A plant’s roots can survive long-term submersion with enough dissolved oxygen. There are two primary reasons for hydroponic root rot. It is the lack of oxygen or the presence of Pythium fungus or another pathogen like bacteria or mold.
Causes of rotting roots in hydroponic systems include:
- Insufficient root exposure to air
- Contaminated nutrient solutions
- Contaminated equipment
- Water molds and pathogens, especially the Pythium species of fungus
- High water temperature reduces oxygen levels
Sources of pathogens often come from infected transplants. The Pythium dissotocum species can thrive in water temperatures of 60 to 85°F (15.5 to 29.4°C). To avoid crops from dying, try keeping roots healthy with a hydroponic water chiller.
How to Identify Root Rot in DWS Systems and Other Hydroponics
Most commercial hydroponics use Deep Water Culture (DWC), but root rot has the same symptoms no matter the growing method.
The roots of a plant are essential for its health. The first sign of the problem is the leaves. Leaves may start to wither and droop, depending on the plant. They may have yellow spots or brown edges. In other words, if the plant does not look healthy in a hydroponic system, check the roots immediately.
Some symptoms of hydroponic root rot include:
- Blackened roots that smell like mushrooms
- “Damping off” or collapse of the seedlings
- Reduced root mass
- Root discoloration, typically yellow or brown
- The plants grow unevenly across the growing platform
Note: Too high chlorine or salts can also look like Pythium root rot. Commercial growers should have their water tested professionally to find the exact cause.
During the first stages of root rot, a slime coating forms around the roots, and it is strong enough to block oxygen from reaching them. The plant’s roots become suffocated and die, while spores from the fungus attach themselves to the dead roots waiting to infect a new area.
Treating Hydroponic Root Rot Problems
If there is an existing problem with pathogens such as Pythium and Phytophthora, the entire system will need to be dismantled and sanitized. Sanitizing everything between cycles should be part of your SOP.
The spores of Pythium and Phytophthora can survive for several months, residing in the dying roots of infected plants. If infected plants contact the nutrient solution, they can contaminate the entire system. People handling diseased plants or parts from a contaminated hydroponic system can reintroduce these spores into a clean system. Growers and visitors should sanitize their hands before entering the area.
To kill the fungus, the nutrient water needs to be changed or treated with a biological fungicide. A biological fungicide introduces “good” microbes into the system, where they destroy the harmful microbes. It is a natural solution, unlike a synthetic fungicide. Currently, there are no synthetic fungicides approved for edible plants.
Another safe method uses ultraviolet light or ozone to kill bacteria and fungus in the water circulation system.
There are riskier chlorine and hydrogen peroxide treatments available, but they can also kill the plants. Laboratory tests show that chlorine levels at 0.5 ppm or higher can cause phytotoxicity.
Unfortunately, if root rot is already in the system, there is little you can do to cure it. Usually, you need to sanitize, start over, and use preventative measures to keep it from reoccurring.
How to Prevent Root Rot in DWC Hydroponics?
Since treating plants that already suffer from hydroponic root rot is usually futile, prevention is your best plan moving forward with future crops. When it comes to hydroponic growing rooms, you must start and stay clean.
Think of your grow room as a hospital operating room. Any pathogens that make their way inside can infect the entire room.
Clean, Sanitize and Inspect
Clean the entire growing area from top to bottom. Sanitize components that contact the growing solution or the plants, such as the reservoir, tubing, and trays. Workers and visitors must wash and sanitize their hands before handling plants or equipment.
If you notice any dead leaves or plant matter in the reservoir, remove it immediately. They can trigger pathogen growth.
Before adding them to the garden, inspect seedlings for pathogens, especially the roots. One infected plant can wipe out the entire crop.
Biofungicides are cultures of living organisms used to control pathogenic fungi and bacteria. It is mixed with water and applied with a sprayer. The beneficial microorganisms consume or kill the pathogens responsible for root rot and other symptoms.
There are about 20 species registered to control root disease in edible plants.
Adding Oxygen to the Solution
Dissolved oxygen is critical to root health. Using an aerator in the reservoir will add dissolved oxygen. For example, lettuce needs 6 to 8 ppm oxygen to thrive. Your best solution is to use an aerator and chill the water to hold more oxygen.
Change the Water
One rule of thumb about changing the water is if you’ve topped up the reservoir enough times to equal its capacity, it is time to change. Other reasons to change the water include:
- The presence of Pythium
- Adding biofungicides is not effective
- Unable to maintain correct pH levels
- Unable to maintain the right EC (electrical conductivity) levels
The ideal pH levels for plants are 5.5 to 6.5. EC is a measure of nutrients in the water. Plants do best when EC levels are 1.2 to 2.0.
Don’t Disturb the Plants’ Roots
The root system is relatively delicate. Handle the roots as little as possible to prevent breakage or contamination.
Avoid Light from Reaching the Water
It’s good to seal any gaps around the plants to prevent light from entering the growing medium. Sunshine and grow lamps can promote harmful bacteria, molds, and fungus growth. Never use clear tubing or walls on your system.
Preventing Root Rot in Hydroponics with Temperature Control
The main reason for regulating temperature is to prevent the growth of pathogens like Pythium from proliferating and causing root decay. Chilling and maintaining water temperatures at or below 60°F (15.5°C) reduces the ability of the fungus to grow. That can be a challenge for growers in hot climates.
Growing solutions at lower temperatures hold more oxygen. Hydroponic water chillers keep the growing solution at a pre-set temperature for optimal oxygen absorption.
Selecting a Water Chiller
When choosing the best hydroponic water chiller, there are a few elements to consider:
- Purchase a chiller that is the correct size for your system
- It must be easy to clean
- All components must be of non-corrosive materials
- Portability is essential to meet changing grow room configurations
- Use a reliable thermostat controller to maintain temperatures 24/7
- Automated and smart controls to monitor the chiller remotely
- Environmentally acceptable r134a or r404a refrigerants
To properly chill hydroponic reservoirs, North Slope Chillers integrates with a product called Fluxwrap. The Fluxwrap surrounds the reservoir tank like a blanket, and the cooling liquid flows through tubing inside. It is the best method to chill hydroponic reservoirs because the growing solution does not contact the chiller or internal components. The heat radiates through the tank wall and into the Fluxwrap.
The added benefit is that the Fluxwrap keeps light out of opaque plastic reservoir tanks. It comes in standard tank sizes of 5-, 15-, 30-, 55-, and 275-gallon tanks or IBC totes. Custom tank sizes are available.
The Fluxwrap and chiller system uses a multi-channel flow throughout the wrap. Elastic straps ensure a tight fit. The Fluxwrap conforms to irregular surfaces and maintains thermal contact over the entire surface without hotspots. It comes complete with an insulated wrap to prevent condensation, which can be a source of pathogens like Pythium or molds.
You can download the chiller catalog here to determine the correct solution for your growing operation.
Industrial water chillers for hydroponics are an investment. They require electricity and a small space. It’s best to place them outside of the growing room to dissipate the heat and reduce any noise it produces. Depending on the grower’s operational requirements, they can circulate from 1 gallon per minute to 654 gallons per minute.
Controlling Root Rot
There is no magic bullet to control Pythium fungus in grow rooms. It’s all about prevention. Keep an eye on your crops and regularly inspect the roots and leaves.
Biofungicides can help reduce the harmful effects of Pythium and other fungi on edible plants. Keeping water temperatures low is an excellent way to minimize root problems in hydroponic growing operations.
Adding oxygen, cleanliness, and cool growing medium temperature all play a role in a successful hydroponic harvest. Portable chillers and fluid channel cooling blankets make it simple to chill hydroponic water reservoirs. Without disruption, these mobile solutions apply direct, even cooling to your hydroponic process.