A Kalanchoe is a popular, easy-to-care-for succulent known for its thick, vibrant leaves and colorful blooms. Despite its hardiness, yellowing leaves (chlorosis) are a common sign of distress. This discoloration indicates the plant is struggling to produce chlorophyll, the pigment responsible for its green color and ability to photosynthesize. Determining the cause requires careful observation, as issues range from improper watering to nutrient imbalances.
Root Issues Caused by Watering Imbalances
Improper watering is the most frequent cause of yellowing leaves in Kalanchoe. As a succulent, the Kalanchoe stores water in its fleshy leaves and stems. Overwatering leads to root suffocation because saturated soil displaces the oxygen needed for healthy root function, often resulting in root rot.
When overwatered, the leaves turn a translucent or mushy yellow, starting with the older, lower foliage. The stem may also become soft, and the roots will appear dark brown or black and feel slimy. To correct this, allow the plant to dry out completely, trim any diseased roots, and repot into fresh, well-draining succulent mix.
Conversely, underwatering can also cause chlorosis. A Kalanchoe not receiving enough water draws moisture from its leaves to survive. This causes the foliage to shrivel, wrinkle, and become crispy as they turn yellow or brown, giving the plant a wilted and dry appearance.
Addressing underwatering requires a thorough soaking until water drains freely, ensuring the entire root ball is rehydrated. To maintain balance, allow the top two inches of soil to dry out between waterings. Consistent monitoring of soil moisture prevents the roots from sitting in perpetually damp conditions while ensuring adequate hydration.
How Light and Temperature Affect Leaf Color
The Kalanchoe’s need for specific light conditions directly impacts its ability to produce chlorophyll. Inadequate light forces the plant to stretch its stems (etiolation), resulting in weak, pale, and yellowing leaves that lack color intensity. Kalanchoe thrives best in bright, indirect light, requiring several hours of high light exposure daily.
Exposure to intense, direct afternoon sun can also cause yellowing due to sun scorch. This damage manifests as bleached or scorched patches on the leaves, which may turn a rapid, widespread yellow or white. The plant should be moved slightly away from the window or shielded from the harshest midday rays.
Temperature stress, particularly exposure to cold drafts or drops below 50°F (10°C), can shock the plant and induce chlorosis. The cold damages the plant’s cell structure, leading to yellowing, wilting, and premature leaf drop. Maintain a consistent indoor temperature, ideally between 65°F and 85°F (18°C and 29°C).
Identifying Nutrient Deficiencies in Soil
While Kalanchoe plants are not heavy feeders, a lack of specific macronutrients can lead to chlorosis. Nitrogen deficiency is a common issue resulting in a generalized yellowing of the older leaves. This occurs because nitrogen is a mobile nutrient, meaning the plant pulls it from older foliage to support new growth.
Deficiencies in immobile micronutrients, such as Iron and Magnesium, cause interveinal chlorosis. In this pattern, the tissue between the leaf veins turns yellow while the veins themselves remain green. This appears first on the newer, upper leaves because the plant cannot move the nutrient from older tissues to the new growth.
Addressing nutrient-related yellowing involves repotting the Kalanchoe into a fresh, well-aerated succulent mix. During the active growing seasons of spring and summer, a balanced, diluted liquid fertilizer can be applied sparingly. Fertilizing during the dormant winter months is unnecessary and can lead to a harmful buildup of salts in the soil.
Diagnosis and Treatment of Pests and Diseases
Yellowing leaves can be a symptom of a biotic attack from pests or diseases. Sap-sucking pests like mealybugs, aphids, and spider mites damage the Kalanchoe by piercing the leaf tissue and extracting fluids. This continuous feeding causes localized yellow spots, overall leaf mottling, and eventual chlorosis.
Mealybugs appear as tiny, white, cottony masses in leaf axils and along the stems. Aphids are small, pear-shaped insects, and spider mites leave behind fine webbing. These pests also excrete honeydew, a sticky substance that encourages the growth of sooty mold.
Fungal and bacterial diseases, particularly those causing root and crown rot, can also lead to systemic yellowing and wilting. These diseases are a secondary consequence of chronic overwatering. Symptoms include dark, water-soaked spots on the leaves or the blackening and softening of the stem tissue.
Pests can be treated by wiping affected areas with a cotton swab dipped in rubbing alcohol, or by applying insecticidal soap or neem oil. If severe fungal or bacterial rot is suspected, the affected plant parts must be promptly pruned. Cultural conditions, especially watering frequency and soil drainage, must be corrected.