Slime-covered roots indicate a larger problem in a hydroponic growing system, usually a disease known as root rot. Root rot is caused by an imbalance in the system that needs to be corrected or the disease will just continue. Removing root rot isn't as easy as cleaning off slime, although treatment will result in clean roots.
Symptoms of Rot
Some types of root rot, also known as dampening-off, produce slime. Fusarium causes a white slime, while pythium is usually brown or black. It is difficult to fully eradicate either one, although pythium is particularly stubborn. Root rot begins in the root system but works its way up the entire plant. Shortly after the infection spreads, plants wilt under the light of day but stand up at night. Roots eventually become brittle and die off and then the plant dies.
Pull dead roots off by hand, if they are accessible. Dead roots will only rot further, making the disease more difficult to cure. Add an air pump or air stone -- or additional ones -- to your reservoir to add more oxygen to the system. If possible, isolate infected plants into their own reservoir so they don't spread the infection to healthy plants. After removing them, flush the system and start fresh with your healthy plants.
The Oxygen Key
Low oxygen is a major cause of rot. Fight the disease by adding oxygen to the system. One of the easiest ways to add oxygen is with the addition of hydrogen peroxide (H2O2). When this unstable element is added to the plants, it breaks down and releases the extra oxygen unit into the medium that water alone doesn't have. There are various concentrations of H2O2 on the market, and any you choose should be labeled "food grade," which means that there are no toxic impurities. It can be found at a hydroponics specialty store, a local feed mill or even at the hairdresser supply store where it is used as a bleaching agent.
How to Use the Solution
The most economical option for purchasing food grade H2O2 is 35-percent concentration, but it needs to be diluted down to a 3-percent solution to use on plants. Wear long pants, sleeves, gloves and protective eyewear while mixing, since it can burn and bleach your skin. Add one part of 35-percent H2O2 to 11 parts water to create a solution that is safe for plants. The optimal amount of solution to use is 2.5 teaspoons per gallon of water, and then replace 25 percent of that total amount every day. For example, in a 4-gallon reservoir, add 10 teaspoons of 3-percent H2O2. Each day thereafter, add 2.5 teaspoons. For the first few weeks, begin with 1 teaspoon per gallon and work your way up to the recommended dose.
Prevention is Best
As with most plant ailments, prevention of root rot is the best medicine, but excellent prevention practices can also help to cure current diseases. High temperatures over 80 degrees Fahrenheit encourage rot growth. The ideal temperature for a hydroponic garden is 68 to 72 degrees F. Constant aeration from a pump or air stone is also important to keep the all-important oxygen flowing. High pH can also be a factor and ideally should be 6.2 or less. Keeping a lid on the reservoir will keep out light as well as any foreign materials that could contaminate the water.
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