The Ginkgo biloba, often called the Maidenhair Tree, is a unique species referred to as a “living fossil” due to its ancient lineage. Celebrated for its distinctive fan-shaped leaves and remarkable resilience, the ginkgo thrives even where other trees struggle. Despite its tough nature, owners may observe the tree’s normally emerald foliage turning yellow outside of the expected season. This yellowing can signal a range of issues, from a normal process to an environmental stressor, and understanding the difference is key to proper care.
Seasonal Yellowing: The Natural Process
The most common reason for yellowing is senescence, a natural process preparing the tree for winter dormancy. This change is triggered by two main factors: the decreasing photoperiod, or shorter daylight hours, and cooler autumn temperatures. As the tree prepares for the cold, it begins to break down the chlorophyll, the green pigment responsible for photosynthesis.
As the chlorophyll degrades, it reveals other pigments, primarily the yellow-hued carotenoids. These pigments transform the ginkgo’s canopy into a brilliant gold color. The synchronization of this process is a defining characteristic of the species, often resulting in a uniform color change across the entire canopy.
This beautiful display culminates in a phenomenon unique to the ginkgo, where the leaves often drop all at once, sometimes within 24 hours. If the yellowing occurs suddenly and uniformly in late autumn, typically October or November, it is a sign of a healthy tree successfully entering its dormant phase. This natural cycle requires no intervention from the owner.
Causes Related to Watering and Environmental Stress
If yellowing occurs outside of late autumn, it often points to a problem with moisture balance, the most frequent cause of non-seasonal distress. Both too much and too little water can result in yellowing, but the symptoms present differently. Overwatering causes roots to suffocate because soil pores remain saturated with water instead of air, leading to root rot.
This lack of oxygen prevents the roots from functioning properly, causing the leaves to wilt and turn a uniform yellow, sometimes with brown tips or edges. Conversely, underwatering causes drought stress, where the tree prematurely sheds leaves to conserve moisture. Drought-stressed leaves often become dry, curl, and may develop brown, scorched edges.
Young trees are particularly susceptible to water stress during their first two to three years as they establish their root systems. To avoid these issues, owners should practice deep, infrequent watering, allowing the top several inches of soil to dry out completely before watering again. Checking the soil moisture with a probe or finger before applying water is a simple technique to maintain the proper balance.
Environmental pressures beyond water can also cause premature yellowing, especially in newly planted specimens. Transplant shock, the stress a tree experiences after being moved, can cause temporary yellowing and leaf drop following planting. Severe heat stress can similarly cause a washed-out, yellowish hue or even leaf scorch, as the tree struggles to regulate its temperature and moisture levels.
Yellowing Due to Soil and Nutrient Issues
If yellowing is not seasonal or related to water volume, the cause may lie in the soil’s chemical composition. Yellowing caused by a nutrient deficiency is known as chlorosis, occurring when the tree cannot produce enough chlorophyll. While ginkgos are notably tolerant of various soil types, they can still suffer from deficiencies in certain micronutrients, particularly iron (Fe) and manganese (Mn).
The visual cue for iron or manganese chlorosis is an interveinal pattern: the tissue between the leaf veins turns yellow while the veins remain green. This pattern often starts on the newer, younger leaves at the tips of the branches. The underlying issue is not always a lack of the nutrient itself, but rather its unavailability due to high soil alkalinity.
In alkaline soils (pH higher than 7.0), iron and manganese chemically bind to other compounds, rendering them insoluble and inaccessible for root uptake. Even if the soil contains an abundance of these elements, the tree cannot absorb them. A professional soil test is the most reliable way to confirm the soil’s pH and nutrient status before attempting any corrective measures.
If a nutrient issue is confirmed, solutions involve adjusting soil chemistry or providing the nutrient in a readily absorbable form. Applying acidifying soil amendments, such as elemental sulfur, can gradually lower the soil pH over time to release the locked-up nutrients. For a faster response, liquid chelated iron or manganese can be applied directly to the soil or foliage, providing an immediate source of the missing micronutrient.