The Aglaonema, commonly known as the Chinese Evergreen, is a popular houseplant valued for its colorful and patterned foliage. When the leaves begin to turn yellow (chlorosis), it signals the plant is experiencing significant stress due to a problem with the environment or care routine. Understanding the specific patterns of discoloration allows for a systematic diagnosis to quickly return the plant to a healthy state.
The Primary Cause: Improper Watering
The majority of yellowing issues trace back to incorrect soil moisture levels, with overwatering being the most frequent culprit. Consistent saturation deprives the roots of necessary oxygen, leading to cellular death and the fungal development of root rot, which manifests as yellowing leaves. Overwatering typically presents as widespread yellowing starting with the older, lower leaves, which often feel soft or mushy.
To avoid this, water only when the top 50% to 60% of the soil volume has dried out, checking with a finger or moisture meter. Ensure the pot has adequate drainage holes and that water flows completely out the bottom when watering. Conversely, underwatering causes a more uniform yellowing, often resulting in dry, crispy, or papery leaves, especially on older foliage. Consistent moisture is preferred, as alternating between bone-dry and saturated conditions places severe stress on the plant.
Light Intensity and Environmental Stress
Aglaonema plants thrive in conditions that mimic their native tropical understory, preferring bright, indirect light. Placement in direct, harsh sunlight, such as an unobstructed south-facing window, causes rapid yellowing and often develops scorched, brown patches. The excessive solar energy destroys the chlorophyll, leading to a pale and sun-bleached appearance.
Too little light can also cause yellowing, as insufficient light compromises photosynthesis, resulting in the plant sacrificing older leaves to conserve energy. Environmental factors like temperature and humidity also induce stress that causes chlorosis. Aglaonemas are sensitive to cold drafts and prefer temperatures between 70 and 85 degrees Fahrenheit. Exposure to a sudden cold draft can result in widespread yellowing and leaf drop. A lack of humidity (ideally 60% to 70%) causes the leaf tips and margins to turn brown and crisp before the entire leaf yellows.
Identifying Nutrient Deficiencies and Toxicity
Yellowing can signal an imbalance in nutrient uptake, known as chlorosis, caused by deficiencies in essential elements like nitrogen, iron, or magnesium. A nitrogen deficiency, for instance, first appears on older leaves, causing them to turn pale yellow across the entire leaf blade as the plant mobilizes limited nitrogen to new growth. Magnesium deficiency, in contrast, typically results in interveinal chlorosis, where the tissue between the leaf veins yellows while the veins remain green.
Over-fertilization, or salt toxicity, presents a different problem. An excessive buildup of mineral salts in the soil burns the fine root hairs and inhibits water absorption. This toxicity causes yellowing and browning specifically along the leaf tips and margins. To prevent salt buildup, periodically flush the soil by watering heavily and allowing a large volume of water to drain through the pot. Fertilization should be applied conservatively, typically during the spring and summer growing seasons, using a balanced, diluted houseplant fertilizer.
Pests, Disease, and Natural Leaf Shedding
Less common but significant causes of yellowing include infestations from sap-sucking pests, which drain the plant of its internal fluids. Pests like spider mites, mealybugs, and scale insects feed on the leaf tissue, leading to a yellow speckling or patchy discoloration that indicates localized cell damage. These infestations often target weakened plants and require prompt treatment with insecticidal soap or neem oil.
Fungal and bacterial diseases, particularly root rot, also present with yellowing foliage, often accompanied by wilting or dark spots. Fungal leaf spot, for example, appears as dark, irregular spots that may be surrounded by a yellow halo. Finally, distinguish stress-induced yellowing from natural leaf senescence. It is normal for an Aglaonema to occasionally shed an older, lower leaf; this natural process involves the leaf turning entirely yellow and drying up, usually affecting only one or two leaves at a time.