What is root rot?
Healthy roots on an African violet are white. Roots that are brown have died and must be removed. Violets can look perfectly healthy and have a ton of blooms and yet be dying of root rot. If you violet wobbles or twists in its pot, that might be another sign the roots are rotting.
Root rot can be caused by a number of factors. First, you might be overwatering your violet. You may need to lighten your potting mix with perlite. However, you can also get root rot by not watering enough. If the soil dries out completely between waterings, some of the violets roots might die and start rotting.
To get rid of root rot, remove all the brown roots. You will probably have to cut off the entire root ball. This sounds drastic but it needs to be done. There is a possibility that the root rot has gone into the stem (also called the neck). You will be able to see that after you cut off the root ball. If there is any brown in the cross-section of the stem that you just cut you will need to keep cutting out the stem until you don't see the brown anymore. Root rot is like cancer. If you don't get it all, it will just keep eating the plant.
The outside of the stem will have some callusing on it where the old leaves were attached. Take a knife or your fingernails and scrape off that callus as you would scrape a carrot until you have a nice green stem. Dust the neck lightly with rooting hormone. Place in new potting mix. To prevent the plant from wilting or going into shock from losing part or all of its root system, place the plant under a dome or inside a Ziploc bag to create added humidity. This acts like an ICU. Use toothpicks to keep the bag from touching the leaves. If the leaves touch the bag, it may damage the leaves or cause them to rot.
Put the bagged violet in a well lighted area, but don't let it get any direct sunlight. Direct sunlight will raise the temperature in the bag and cook the violet.
Leave the violet in the bag for two to four weeks or until you are able to tug gently on the violet without it coming out of the soil.
If you don't need to remove all the roots, it's still a good idea to put the violet under a dome or in a bag to prevent shock.
Thanks to larry_b for your contributions to this FAQ!.