Most of the time, when root rot sets in, it's too late to save your plant. However, if you catch root rot before it takes hold of the entire root system, you stand a chance of saving the plant. If you don't catch it in time, bacterial overgrowth chokes out the root system, and the dead roots rot and decay.
Wash the Roots
Bacteria and fungus overtake a plant's roots when the plant is over watered or exposed to diseases that lead to root rot. Rinsing the soil away from the plant's roots usually washes away these organisms. Thoroughly rinse your plant's roots once you wash away the soil to remove slimy residue.
Clip Rotted Roots
If rot has not spread to all of the roots, clip off the infected roots. Remove brown, black or mushy roots. Losing a substantial portion of the root system is as dangerous to a plant as root rot; if too many roots have to be pruned, your plant likely won't survive.
Disinfect the Pot
After you've thrown away the infected soil and washed the roots, kill remaining bacteria in the pot before replanting. Soak the pot in a simple bleach solution of one part bleach to nine parts water. This sanitizes the container and helps avoid reinfection.
Change the Soil
Do not re-pot a plant with root rot in the same soil from which it was removed. Root rot-causing organisms thrive in moist soil conditions and attack the root system as soon as you replant. Use a pasteurized soil. If you are not sure if your soil is pasteurized, place it into a glass bowl and microwave it until it is hot enough to kill bacteria and fungus.
Treat With Hydrogen Peroxide
According to Quick Grow South, hydrogen peroxide in a three-percent solution helps fight root rot and encourages new, healthy root growth. Water the plant with peroxide after you re-pot it. Use a mixture of two-and-a-half teaspoons of peroxide per gallon of water; use the mixture at every watering, even after the plant is healthy.