Yellow leaves, known as chlorosis, are the most frequent complaint among Mandevilla owners. This symptom is not a disease but a signal that the tropical vine is experiencing environmental stress or a resource imbalance. Mandevilla plants are native to warm, humid climates and thrive when their needs for light, water, and nutrients are consistently met. Pinpointing the cause of the yellowing is the first step toward restoring the plant’s deep green foliage.
Watering and Drainage Issues
Improper soil moisture is the most common reason Mandevilla leaves yellow and drop. The plant requires consistent moisture but cannot tolerate “wet feet,” meaning it should never sit in soggy, waterlogged soil. Overwatering quickly leads to root rot, a fungal condition where roots are deprived of oxygen and begin to decay. This prevents the uptake of water and nutrients, often causing widespread yellowing of the lower leaves, which may then turn brown and fall off.
To check the moisture level, insert your finger about two inches into the potting mix. If the soil is still damp at this depth, withhold watering until the top layer has dried out completely. If the soil is oversaturated, immediately stop watering and ensure the container has unobstructed drainage holes. For severely waterlogged plants, removing the plant to allow the root ball to air-dry slightly before repotting into fresh, well-draining soil may be necessary.
Under-watering can also cause yellowing, though it is less common for this species due to its water-storing root system. When significantly dehydrated, the leaves often turn pale yellow, sometimes curl, and feel brittle before they drop. The goal is to maintain a consistently moist, but not saturated, soil environment. This is best achieved by using a high-quality potting mix amended with materials like sand or perlite to improve drainage.
Light and Temperature Stress
As a tropical plant, Mandevilla requires significant light exposure, ideally receiving six or more hours of sun daily. Insufficient light exposure causes the plant to conserve energy by sacrificing older leaves, leading to general yellowing, especially on lower, shaded sections of the vine. If the plant is moved too quickly from a low-light area to intense, direct afternoon sun, the leaves can suffer from sunscald. This tissue damage appears bleached or scorched, often preceded by yellowing.
The plant is highly sensitive to temperature fluctuations and cold exposure, which can induce physiological shock. Mandevilla thrive in warm conditions, with an optimal range between 68 and 90 degrees Fahrenheit. Temperatures consistently falling below 50°F (10°C) cause the plant to enter a state of stress, resulting in widespread yellowing and leaf drop. Cold drafts or placing the plant near a cold window during seasonal transitions can trigger this response.
Nutrient Deficiencies and Soil pH
Yellowing can signal chlorosis caused by a lack of specific micronutrients needed for chlorophyll synthesis. Nitrogen deficiency is a common culprit, presenting as uniform yellowing of the oldest leaves first, as the plant moves this mobile nutrient to support new growth. Conversely, Iron (Fe) deficiency causes interveinal chlorosis, where the newest leaves turn yellow while the veins remain green. This distinct pattern occurs because iron is an immobile nutrient that cannot be relocated.
Magnesium (Mg) deficiency also causes interveinal chlorosis, but symptoms appear on the older, lower leaves first. Addressing these issues requires a soil pH test, as Mandevilla prefers a slightly acidic environment (pH 6.0 to 6.5). If the soil becomes too alkaline (high pH), essential micronutrients like iron become chemically unavailable for root absorption. Applying a balanced, slow-release fertilizer during the growing season is recommended, and for alkaline soil, an acidic supplement like chelated iron can help unlock necessary micronutrients.
Pests and Diseases
Sap-sucking insects can cause yellowing by extracting plant fluids and chlorophyll from the leaves.
Common Pests Causing Yellowing
Spider mites are tiny pests that cause stippling—a fine pattern of yellow or white dots on the foliage—and are often confirmed by fine webbing on the undersides of leaves and stems.
Mealybugs appear as small, cottony white masses, typically found in leaf axils and stem crotches, and their feeding causes localized yellow spotting and leaf distortion.
Scale insects appear as small, brown or gray waxy bumps on the stems and leaves. Their feeding results in yellowing and the secretion of a sticky substance called honeydew.
Fungal leaf spot diseases, while less common, can also cause yellow discoloration that often progresses to brown lesions.
For minor infestations, pests can be dislodged with a strong jet of water or by wiping the leaves with a cotton swab dipped in rubbing alcohol. More persistent issues are managed by applying a horticultural oil, such as neem oil, or an insecticidal soap directly to the affected areas. Ensure complete coverage, especially on the undersides of leaves.