Eggplant, a member of the nightshade family (Solanaceae), is a warm-weather crop prized for its glossy, deep purple fruit. Yellowing, whether on the fruit or the leaves, signals that the plant is experiencing stress. This color change, known as chlorosis in foliage, indicates that the plant’s chlorophyll production is disrupted. Identifying the specific pattern and location of the yellowing is the first step in diagnosing the problem.
When the Eggplant Fruit Itself Turns Yellow
The most frequent reason for a mature, dark-colored eggplant fruit to turn yellow is simple overripening, which is a natural stage of senescence. Eggplants are typically harvested before they reach full botanical maturity, ideally when the skin is still taut and glossy. When the fruit remains on the plant too long, the skin changes color from purple or black to a dull yellow or brown as the seeds inside fully develop and harden. This color change indicates that the flesh has become spongy, tough, and often bitter, making it less palatable for eating. Another cause of fruit yellowing is sun scald, where intense, direct exposure to sunlight causes a bleached, yellow, or tan patch to form on the exposed side of the fruit.
Leaf Yellowing from Nutrient Deficiencies
When the leaves begin to yellow, a lack of essential nutrients is often the cause, known as chlorosis. The location of the yellowing on the plant—old growth versus new growth—is the best indicator of which element is missing.
Nitrogen deficiency is a common issue because it is a mobile nutrient, meaning the plant moves it from older leaves to support new growth. This results in the overall pale-yellowing of the entire older leaves, often beginning at the bottom of the plant, while the newer leaves may appear light green.
Magnesium is another mobile nutrient, and its deficiency also appears first on the older, lower leaves. However, magnesium deficiency presents a distinct pattern called interveinal chlorosis, where the tissue between the leaf veins turns yellow while the veins themselves remain green. This pattern is often corrected by applying a foliar spray of a magnesium source, such as Epsom salts.
In contrast, iron is an immobile nutrient, so its deficiency affects the youngest, newest leaves first. This also results in interveinal chlorosis, where the new growth is pale yellow with green veins. This is frequently seen in alkaline or waterlogged soils, which can lock up the iron and prevent the roots from absorbing it. Correcting a nitrogen deficiency typically involves applying a balanced fertilizer, while addressing a mineral deficiency often requires adjusting soil pH or using a targeted foliar spray.
Leaf Yellowing Caused by Pests and Pathogens
Pests and pathogens can cause localized or systemic yellowing of eggplant leaves. Sap-sucking insects like spider mites feed on the underside of leaves, extracting chlorophyll and causing a fine yellow or white stippling pattern across the foliage. In heavy infestations, tiny webs may be visible, and the overall plant vigor will decline. Aphids also cluster on new growth, causing a localized yellowing and often leaving behind a sticky residue called honeydew. These pests can usually be managed with targeted applications of insecticidal soap or horticultural oil.
More serious causes of leaf yellowing are soil-borne fungal diseases like Verticillium wilt and Fusarium wilt. These pathogens invade the plant’s vascular system, blocking the flow of water and nutrients. The classic symptom of Verticillium wilt is the sudden yellowing and wilting of leaves, often affecting only one side of the plant or a single branch first. As the disease progresses, the yellowing spreads and the plant eventually collapses, which is problematic since these fungal wilts are difficult to treat.
Stressors from the Growing Environment
Environmental factors are a major source of stress that can lead to leaf yellowing. Water stress is a frequent culprit, and both overwatering and underwatering can produce similar symptoms. Overwatering is particularly harmful because it starves the roots of oxygen, leading to root rot, which prevents the plant from absorbing water and nutrients. This results in a general, widespread yellowing and a limp, drooping appearance.
Conversely, an underwatered eggplant will initially show leaves that wilt dramatically during the heat of the day, but they may recover overnight. If the drought stress continues, the leaves will turn yellow, become dry and brittle, and eventually drop off. Maintaining consistent, deep soil moisture without saturation is paramount for eggplant health.
Temperature and light conditions also play a significant role in plant health. Eggplants thrive in warm conditions, and exposure to cold temperatures or a sudden cold snap can shock the plant, causing the leaves to yellow and drop quickly. Newly transplanted eggplants may exhibit temporary yellowing or wilting, known as transplant shock, as they adjust to the new environment. Providing a layer of organic mulch helps stabilize soil temperature and moisture, mitigating many of these common environmental stressors.