The Plumeria, commonly known as Frangipani, is a popular tropical plant cherished for its fragrant, vibrant flowers. Yellowing leaves followed by leaf drop is the most frequent sign of distress for this plant. Diagnosing the problem requires a systematic approach, as the symptom can be caused by environmental, biological, or nutritional issues. This guide identifies the visual cues needed to accurately determine why your Plumeria is shedding its foliage.
Improper Watering and Temperature Stress
Watering issues are the most common cause of yellowing Plumeria leaves, though both overwatering and underwatering produce similar symptoms. Overwatering leads to saturated, anaerobic soil conditions, preventing roots from absorbing oxygen and causing root rot. Yellowing typically begins on the older, lower leaves and progresses upward, sometimes accompanied by a soft or mushy trunk near the soil line.
Conversely, underwatering also causes leaves to yellow and drop as the plant attempts to conserve moisture through self-pruning. The soil may pull away from the pot’s edges, and leaves might develop crispy, shriveled edges or appear uniformly yellow before falling. The most effective solution is to allow the top few inches of soil to dry completely before providing a deep, thorough watering.
Temperature shifts can also induce rapid leaf drop, as Plumeria are highly sensitive to cold. A sudden temperature drop below 50 degrees Fahrenheit can cause the plant to immediately shed its leaves in a protective response known as cold shock. Excessive heat or sunburn can also cause leaves to yellow and shrivel.
Diagnosing Nutrient Shortages
If watering and temperature are ruled out, the pattern of yellowing, known as chlorosis, can point to a specific nutrient shortage. Nitrogen deficiency is frequent, presenting as a generalized, pale-yellow discoloration starting on older, lower leaves. Since nitrogen is a mobile nutrient, the plant relocates it from old foliage to support new growth, causing the older leaves to suffer first.
A lack of Magnesium, also a mobile nutrient, shows up in older leaves. The symptom is interveinal chlorosis, where the tissue between the leaf veins turns yellow while the veins remain dark green. This creates a characteristic “V” pattern specific to magnesium deficiency.
Iron deficiency is not mobile within the plant, so symptoms appear first and most severely on the youngest leaves. New growth displays bright yellow or nearly white coloration, but the leaf veins stay green. This mirrors the interveinal chlorosis of magnesium deficiency but affects new growth instead of old. Magnesium deficiency can be corrected by applying Epsom salts (magnesium sulfate) to the soil.
Identifying Common Pests and Diseases
Biological agents like pests and fungal diseases cause yellowing and leaf drop, usually accompanied by other visible evidence. Plumeria Rust, caused by the fungus Coleosporium plumeriae, is a common and recognizable disease. Its presence is marked by small, yellow spots on the upper side of the leaf, corresponding to bright orange or reddish-brown powdery pustules on the underside.
These pustules are masses of microscopic spores that can rapidly defoliate an entire tree, though the disease rarely kills the plant. Management involves immediately removing and disposing of all infected leaves. Apply a fungicide, such as one containing chlorothalonil or myclobutanil, to prevent further spread. Good air circulation and avoiding overhead watering limit the humid conditions that favor fungal growth.
Pests such as spider mites and scale insects cause leaf discoloration as they feed on the plant’s sap. Spider mites cause fine stippling or speckling on the leaf surface and may leave behind fine webbing, leading to yellowing and premature leaf drop. Scale insects are immobile, shell-like pests that often cause a sticky residue called honeydew, which attracts sooty mold and leads to yellow, weakened foliage.
Seasonal Shedding and Natural Dormancy
If cultural problems and biological threats are eliminated, yellowing and dropping leaves may be a natural, seasonal process. Plumeria trees are deciduous, meaning they naturally shed their leaves, especially in regions with cooler temperatures or shorter daylight hours. This typically occurs in late fall or early winter as the plant prepares for dormancy.
When dormancy is the cause, the entire plant gradually turns yellow and drops most of its foliage uniformly. This survival mechanism allows the plant to conserve energy and moisture until warmer temperatures return. During dormancy, stop watering the plant almost entirely. The lack of leaves means the plant cannot utilize moisture, making it highly susceptible to fatal root rot.