Why Are My Mandevilla Leaves Turning Yellow?

Observing yellow leaves on a mandevilla vine is a common issue, but it’s often a signal from the plant indicating a specific and correctable problem. This guide will help you diagnose the cause and take the necessary steps to restore your mandevilla’s health and vibrant green foliage.

Improper Watering

An incorrect watering routine is a frequent reason for yellowing leaves on a mandevilla. Overwatering is a common culprit, as persistently soggy soil deprives the roots of oxygen and leads to root rot. This prevents the plant from absorbing nutrients, causing leaves to turn yellow and wilt. An overwatered pot will feel unusually heavy, and the soil surface will be consistently damp.

Conversely, underwatering also causes stress, prompting leaves to turn yellow as the plant conserves resources. In this case, the yellow leaves will feel dry and crispy and may curl inward. To correct your watering habits, check the soil before adding more water. If the top one to two inches feel dry, it is time to water, and ensure the pot has adequate drainage holes.

Nutrient Deficiencies

A lack of proper nutrition can cause yellowing leaves, as the plant cannot produce enough chlorophyll, the pigment that makes leaves green. The specific pattern of yellowing can point to the deficient nutrient. For example, a nitrogen deficiency often appears on older, lower leaves first, as the plant moves this mobile nutrient to support new growth.

Other deficiencies, such as a lack of magnesium or iron, may cause chlorosis, where the leaf tissue between the veins turns yellow while the veins themselves remain green. To address these issues, use a balanced, water-soluble fertilizer formulated for flowering plants. Feed your mandevilla according to the product’s instructions, usually every two to four weeks during the active growing season. Be careful not to over-fertilize, as an excess of salts can also damage the roots.

Pest Infestations

Pests that feed on mandevilla sap can cause leaves to develop yellow spots or turn entirely yellow. Common culprits include spider mites, aphids, and mealybugs, which weaken the plant by draining its nutrients. Inspect your plant carefully, paying attention to the undersides of leaves and where leaves meet the stems.

Signs of infestation include the fine webbing of spider mites, the sticky “honeydew” from aphids, or small, white masses of mealybugs. For minor infestations, wipe the leaves with a damp cloth or use a stream of water to dislodge the pests. For persistent problems, applying a horticultural oil like neem oil or an insecticidal soap is an effective treatment.

Environmental Stress

Environmental stress from improper light or temperature can lead to yellow leaves. While mandevillas thrive in bright conditions, too much direct afternoon sun can scorch the foliage, causing it to turn yellow. Insufficient light also hinders photosynthesis, causing leaves to yellow and drop.

As tropical plants, mandevillas are sensitive to abrupt temperature changes. A sudden drop in temperature, cold drafts, or placement near a cold window can shock the plant and cause yellowing. Place your plant in a spot that receives bright, indirect light. Protect it from temperatures below 50°F (10°C) and keep it away from drafty areas.

Natural Aging Process

Yellowing leaves are not always a sign of a problem but can be part of the plant’s natural life cycle. It is normal for the oldest leaves at the bottom of the vine to gradually turn yellow and fall off. This happens as the plant diverts energy toward producing new growth at its tips.

If only a few lower leaves are yellowing and the rest of the plant appears healthy and is actively growing, there is no reason for concern. As long as the yellowing is confined to the base of a thriving plant, you can simply remove the old leaves to keep it looking tidy.