What is root rot?
Root rot can have two sources, one is a prolonged exposure to overwatered conditions can cause some of the roots to die back due to a lack of oxygen. As they die, they can start to decay or rot away. The rot can then spread to healthier roots and kill them as well, even if the soil conditions are corrected.. The other source can be from a fungus in the soil. The fungus may lay dormant in soil indefinitely and then may suddenly flourish when the plant is overwatered once or twice. The root rot fungus attacks the roots and causes them to die and rot away.