The Pothos plant (Epipremnum aureum) is a popular houseplant prized for its vibrant foliage. When the green or variegated leaves of this tropical vine begin to turn black, it is a clear sign that the plant is experiencing significant stress. This color change signals cellular collapse and requires immediate attention to diagnose the underlying cause. Understanding the specific nature of the blackening is the first step toward restoring your Pothos to health.
Excessive Moisture and Root Distress
The most frequent cause of black leaves on a Pothos is overwatering, which leads to root rot. When the soil remains saturated for extended periods, the oxygen necessary for healthy root function is displaced, creating anaerobic conditions where roots essentially suffocate and begin to decay. This decay is often caused by water mold pathogens like Pythium, which thrive in overly wet environments.
The blackening caused by root distress typically appears as mushy, soft spots that often start near the base of the leaf or stem and spread quickly. If the root rot is advanced, the stems themselves may become brown and mushy, indicating the rot has traveled up from the root system. Healthy Pothos roots are firm and white or light tan, but rotting roots will be dark, soft, and sometimes emit a foul, sulfurous odor. Using a dense potting mix or a container without adequate drainage holes increases the risk of soil saturation and root failure.
Immediate Damage from Cold Exposure
Pothos are susceptible to cold damage, which causes rapid leaf blackening. This damage occurs when the plant is exposed to temperatures below 50°F (10°C) or is placed near cold drafts from windows or air conditioning units. The sudden drop in temperature causes the water inside the plant cells to expand and rupture the cell walls, leading to immediate tissue death.
This type of injury appears quickly, often within hours of exposure, manifesting as black, water-soaked, or transparent areas on the leaves, particularly along the edges or tips. Unlike gradual blackening from root rot, cold damage is usually a sharply demarcated symptom of localized cellular collapse. Any leaves or vines that have turned completely black from cold are permanently damaged and will not recover.
Identifying Pathogenic Black Spots
Blackening can also be caused by bacterial or fungal leaf spot diseases. These diseases typically affect the leaf surface and are often encouraged by high humidity and poor air circulation. Fungal diseases, such as those caused by Rhizoctonia, may appear as irregular, dark, necrotic spots on the leaves.
Bacterial leaf spots, often caused by organisms like Pseudomonas cichorii, present as distinct, water-soaked lesions that turn brown or black. These spots can sometimes be surrounded by a yellow halo, distinguishing them from the larger, mushier areas associated with root rot or the widespread damage from cold. The disease may cause premature leaf drop and can be spread by splashing water, which is why avoiding overhead watering is often recommended.
Steps for Pothos Recovery and Prevention
Once the cause is identified, immediate action is necessary. If root distress is suspected, remove the Pothos from its pot and inspect the roots, pruning away all dark, soft, or slimy sections with sterilized scissors. Repot the plant into a new, well-draining soil mix in a container with confirmed drainage holes to ensure proper soil aeration.
For leaves damaged by cold or disease, prune off all blackened foliage, as this tissue is dead and cannot be revived. Move the plant to a warmer location, ensuring it is away from any drafts or vents that could cause temperature fluctuations. Moving forward, only water the Pothos when the top one to two inches of soil are completely dry to prevent future moisture-related issues.