Root rot is caused by a fungal infection that attacks the plant under the soil's surface, making the roots soft and discolored. Most plants are vulnerable to this condition, unless they are hybrids that are bred to resist the pathogens that cause it. Acute forms of root rot are not treatable and eventually lead to the death of the plant. Chronic or mild forms are treatable. Plants with chronic root rot have yellowed leaves that curl during the day but recover at night. Acute forms of the disease cause blackening of the roots and stems at soil level.
Stop watering the plant. Excess soil moisture leaves plants vulnerable to the pathogens that cause root rot. Unless the plant requires a lot of water (such as those that grow naturally in bogs and marshes), do not water it unless the top inch or two of soil is dry to the touch.
Water away from the base of the plant or tree trunk. A plant's feeder roots are aligned directly under the farthest-reaching branches. This perimeter in the soil is called the drip line. Water the soil in this area. Water poured on or near the main stem or trunk leads to pooling.
Remove the mulch around the base of the plant. Mulch makes soil retain moisture. In the case of root rot, the goal is to dry out the roots as much as possible, and removing the mulch is essential to enabling the sun to help dry out the soil.
Avoid fertilizing while treating root rot. Plants with root rot have compromised systems that do not absorb water or fertilizer correctly.
Drill 18-inch-deep, 2-inch-diameter holes into the soil along the drip line of the plant or tree. Fill these holes with a 1:1 mixture of peat and pumice or baked clay pieces. This mixture will help aerate the soil and drain away excess moisture.