The Kalanchoe is a popular succulent houseplant known for its thick leaves and vibrant blooms. When these robust plants display leaf discoloration, it signals underlying distress. The most common symptom is chlorosis, which is the technical term for leaf yellowing caused by a lack of chlorophyll. Diagnosing the precise cause requires observing the plant’s environment and the specific pattern of yellowing.
Imbalance in Water Management
Improper watering is the most frequent cause of yellowing leaves in Kalanchoe plants, which are adapted to arid conditions. Symptoms of overwatering and underwatering are often confused, but they present with distinct differences necessary for accurate diagnosis.
Overwatering deprives roots of oxygen in saturated soil, often resulting in fungal root rot. This typically causes the leaves to turn yellow and become soft, mushy, or translucent. To prevent this, ensure the pot has drainage holes and use a well-draining succulent mix. Allow the top two to three inches of soil to dry out completely before watering again.
Conversely, an underwatered Kalanchoe experiencing drought stress shows yellowing accompanied by dry, crispy edges or shriveling, particularly in the lower leaves. The leaves might also appear dull or wrinkled as the plant attempts to conserve moisture. The solution is a deep, thorough watering until water flows from the drainage holes. Follow this with a return to a consistent, infrequent schedule.
Light and Environmental Stressors
Kalanchoe plants thrive on bright light, but both extremes of exposure can trigger a stress response that manifests as chlorosis. When a plant does not receive enough light, leaves appear pale and yellow due to insufficient chlorophyll production. A prolonged lack of light also causes etiolation, where stems stretch out weakly toward a light source. Moving the plant to a location with bright, indirect light is necessary to reverse the paleness and prevent further stretching.
Placing the plant in too much direct, intense afternoon sun can result in leaf scorching. This damage appears as bleached yellow or brown patches, often starting at the tips or edges of the leaves. The best placement provides bright, filtered sunlight. Consider a spot near an east-facing window or a few feet away from a south-facing one.
Temperature fluctuations also act as an environmental stressor that can cause sudden leaf yellowing and drop. Kalanchoes are sensitive to cold drafts, and exposure to cold air from windows or air conditioning vents can shock the plant. Maintaining a consistent room temperature, ideally between 65°F and 80°F, helps the plant maintain metabolic stability and prevents cold-induced chlorosis.
Nutrient Imbalances
If watering and light conditions are stable, yellowing leaves may point to a deficiency in essential plant nutrients. Nitrogen deficiency is a common culprit, resulting in a general yellowing that begins with the older, lower leaves. The plant relocates mobile nitrogen from the older foliage to support new growth, causing those leaves to yellow first.
Micronutrient deficiencies, such as those involving iron or magnesium, present as interveinal chlorosis. In this pattern, the veins of the leaf remain green while the tissue between the veins turns yellow. Iron deficiency typically shows on the newest growth. Magnesium deficiency symptoms usually appear on the older leaves first.
Kalanchoes are light feeders, so over-fertilization can cause problems. However, a balanced approach during the growing season can correct deficiencies. Applying a balanced, diluted succulent fertilizer once every four to six weeks during spring and summer is sufficient. Avoid feeding the plant during the dormant winter months when growth slows down.
Diagnosing Pests or Pathogens
Biological threats like pests and diseases can cause yellowing by compromising the plant’s ability to transport water and nutrients. Common sap-sucking pests, such as mealybugs and spider mites, feed on the plant’s juices, leading to localized or widespread yellowing. Mealybugs often appear as small, white, cottony masses in leaf axils or on stems.
Spider mites are harder to spot, but their presence is indicated by fine webbing and a stippled, speckled yellowing pattern on the leaves. Regular inspection of the undersides of the leaves and stems is the first step in pest management. Treating an infestation involves isolating the plant immediately and wiping the foliage with an insecticidal soap or a diluted alcohol solution.
Pathogens, primarily fungal or bacterial diseases, are usually secondary to chronic overwatering and root rot. These issues can cause yellow spots, lesions, or a general decline that eventually turns the entire leaf yellow and mushy. Ensuring the plant is potted in sterile, well-draining media and is not sitting in water is the most effective preventative measure.