The Ginkgo biloba tree, an ancient species and living fossil dating back over 200 million years, is renowned for its distinctive fan-shaped leaves that turn brilliant golden in autumn. It is also remarkably resilient, thriving in diverse environments and resisting diseases, pests, and urban pollution. Despite its many appealing characteristics, certain ginkgo trees are associated with a strong, unpleasant odor.
The Source of the Odor
The unpleasant smell linked to ginkgo trees originates exclusively from female trees. Female ginkgo trees produce fruit-like seeds, the true source of the odor. The smell comes from the fleshy outer layer of these seeds, known as the sarcotesta, not from the tree’s leaves, bark, or flowers.
The “fruits” are plum-shaped, approximately 2.5 cm in diameter, and transition from green to tan or orange as they ripen. They appear and fall in autumn, creating a messy situation when crushed underfoot. Male ginkgo trees produce pollen cones and do not bear these odorous seeds.
The Chemistry Behind the Smell
The ginkgo’s foul smell comes from chemical compounds in the fleshy outer coating of the female ginkgo seed. When these seeds fall to the ground and decompose or are crushed, they release volatile compounds. The primary culprit behind this distinct aroma is butyric acid, also known as butanoic acid.
Butyric acid has a strong, rancid odor, compared to rancid butter, vomit, or stale cheese. Other related carboxylic acids, such as hexanoic acid, also contribute to the pungent smell. The odor’s intensity increases as the fruit decomposes, making autumn particularly noticeable in areas with female ginkgo trees.
Identifying and Managing Stinky Ginkgo Trees
Identifying the sex of a ginkgo tree can be challenging, especially before it reaches reproductive maturity, which can take up to 20 years. Without reproductive structures, it is nearly impossible to determine if a young ginkgo is male or female through visual observation. Nurseries typically sell male cultivars, propagated from cuttings of known male trees to ensure they will not produce smelly seeds.
For existing female ginkgo trees, practical management strategies focus on mitigating the mess and odor. Prompt cleanup of fallen fruit is the most direct way to reduce the smell, as decomposition intensifies the odor. Some cities have experimented with spraying female trees with chemicals, such as chlorpropham (a potato sprout inhibitor), to prevent fruit development, though success can vary, especially if washed away by rain. Homeowners may find such spraying difficult to implement effectively.
In urban planning, male ginkgo trees are preferred due to their pollution tolerance and hardiness, without the fruit nuisance. City planners frequently choose male varieties for street plantings to avoid the odor and the slippery conditions created by fallen, decomposing fruit. If the smell becomes unbearable and other solutions are insufficient, consulting an arborist for removal and replacement with a male tree or another species might be considered. It is worth noting that some male trees have been observed to spontaneously develop female branches or even change sex, though this is rare.