Leaf yellowing on your oleander, known as chlorosis, signals that the plant is under stress. This discoloration is a visible symptom indicating a loss of chlorophyll, not a specific disease. Identifying the pattern of yellowing points toward the underlying issue. Oleanders are resilient, but their health is sensitive to environmental changes or pest attacks. Understanding the cause is the first step toward restoring the plant’s health.
Water and Soil Problems
One of the most frequent causes of yellowing foliage is an imbalance in water intake, with overwatering being the common culprit. When soil remains saturated, oxygen is displaced, leading to root suffocation and root rot. This damage prevents roots from absorbing water and nutrients, resulting in widespread yellowing and a limp, droopy appearance.
Poor drainage exacerbates this problem by trapping excess moisture around the root ball. Oleanders prefer well-draining soil, and a dense, compacted medium often leads to chronic overwatering symptoms. Conversely, severe underwatering can also cause yellowing, often starting at the tips or edges, which become dry and brittle as the plant sacrifices older leaves.
Nutrient deficiencies also trigger chlorosis, and the pattern of yellowing offers a clear diagnostic clue. A lack of mobile nutrients like nitrogen typically causes uniform yellowing across the entire leaf, appearing first on older, lower foliage. If the newest leaves are yellowing while the veins remain green, this interveinal chlorosis is characteristic of an immobile nutrient deficiency, most often iron.
Pests and Diseases
Beyond environmental stress, living organisms can cause the foliage to lose its green color. Tiny, sap-sucking insects are frequent pests that feed on the plant’s vascular system, leading to localized yellowing and leaf drop. Common culprits include oleander aphids, scale insects, and mealybugs.
These pests typically cluster on the undersides of leaves and on new growth, draining the plant’s fluids and causing leaves to become stunted or discolored. Severe infestations produce a sticky substance called honeydew, which encourages the growth of black sooty mold. This mold reduces the leaf’s ability to photosynthesize, compounding the stress.
A more serious biological cause is Oleander Leaf Scorch (OLS), caused by the bacterium Xylella fastidiosa. This bacterium is spread by xylem-feeding insects like sharpshooters and is characterized by yellowing and browning that begins at the leaf margins and progresses inward. OLS is often confused with drought stress, but the infected plant will not recover because the bacteria clog the water-conducting xylem vessels, leading to branch dieback and eventual death.
Fixing the Problem and Long-Term Care
Addressing water issues requires immediate adjustment, starting with checking soil moisture before watering again. For overwatered plants, allow the soil to dry out significantly, and ensure containers have unobstructed drainage holes to prevent standing water. Improving the soil with organic matter enhances aeration and drainage, reducing the risk of future root problems.
To correct nutrient deficiencies, treatment depends on the specific element. A nitrogen deficiency, identified by yellowing of older leaves, can be remedied with a balanced fertilizer application rich in nitrogen, such as ammonium sulfate. For iron chlorosis, applying a chelated iron product directly to the soil or as a foliar spray makes the element available to the roots in alkaline soil conditions.
Managing pests involves non-chemical and targeted chemical treatments. Small infestations of aphids or mealybugs can be controlled by a strong jet of water or by wiping affected areas with rubbing alcohol. For larger outbreaks, applying horticultural oil or insecticidal soap, which smothers the pests, is an effective approach.
Long-term care centers on preventative maintenance, including proper pruning to increase air circulation and reduce conditions that favor fungal issues. Maintaining a regular, deep watering schedule that allows the top few inches of soil to dry between applications is crucial. If Oleander Leaf Scorch is suspected, professional laboratory testing is necessary for confirmation. Removal of the plant is often the only course of action to prevent the spread to other oleanders.