Root rot is a common affliction that can quickly threaten the health of a plant, often beginning unseen beneath the soil line. It occurs when roots are deprived of oxygen (anoxic conditions), allowing anaerobic organisms and destructive pathogens to replace beneficial soil microbes. Early identification is crucial for saving the affected plant, as the decay involves changes both below and above the ground.
The Definitive Appearance of Rotting Roots
A direct inspection provides the most conclusive diagnosis of root rot. Healthy roots appear firm, flexible, and light-colored, such as white or pale tan. In contrast, rotting roots lose their firm structure, feeling soft, stringy, or mushy to the touch. The outer layer, or cortex, of a severely rotted root may even slough off easily when gently handled. The color of a diseased root shifts dramatically, transitioning to shades of dark brown, gray, or black as the roots decay, often accompanied by a foul, unpleasant odor described as sour, fishy, or sulfurous, produced by anaerobic bacteria.
Visible Signs of Root Distress Above Ground
Before examining the roots, a plant suffering from rot will display several symptoms in its foliage and overall structure. A common, confusing sign is progressive wilting, even when the soil remains moist or saturated. The damaged roots cannot absorb water efficiently, mimicking drought symptoms. This failure causes wilting even when the soil is wet. Leaves show discoloration (chlorosis), typically starting with older or lower leaves turning yellow, then brown, and dropping prematurely. Growth will also slow significantly or become stunted, as the compromised root system cannot transport necessary water and nutrients.
Primary Environmental Causes of Root Rot
The cause is almost always an environment where the soil remains waterlogged for extended periods, leading to oxygen deprivation (anoxia). Soil air pockets, necessary for root respiration, become completely filled with water, effectively suffocating the root tissue. Overwatering is the most frequent action creating this waterlogged environment, especially in potted plants. Poor drainage compounds the issue, which can be caused by using a dense potting mix, heavy soil compaction, or a container lacking adequate drainage holes, thus maintaining the anoxic state. Once waterlogged, the environment becomes a breeding ground for destructive soil-borne pathogens, such as the oomycetes Pythium and Phytophthora, which thrive in low-oxygen conditions and attack stressed roots.
Steps for Treating and Repotting Affected Plants
If root rot is confirmed, immediate action is necessary to salvage the plant. First, carefully remove the plant from its pot and gently loosen the soil from the root ball. All old, contaminated soil must be completely removed, often requiring a gentle rinse under lukewarm running water to fully expose the roots. Next, prune away all affected root material using clean, sterilized shears; any root that is dark, mushy, or soft should be cut back to the point where the tissue is firm and healthy. Repot the remaining healthy root system into a clean or disinfected container using fresh, sterile, and well-draining potting mix, and prune back some above-ground foliage to reduce water demand.