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Hanoi's beloved devil's tree
The tree and its scent
The trees bloom in autumn with star-shaped white and green flowers that release a perfume-like scent, and they appear in many romantic songs and poems about the city. Locally they are called hoa sua, which means milk flower. Some residents prefer their other name, devil's tree. One gets a headache from the scent, and another kept his doors and windows shut because he felt under direct attack from the dozens of trees near him.
The city's response
After the complaints came in, the authorities cut back up to 1,000 of the city's 14,000 blackboard trees to reduce the fragrance. It did not appear to work, and officials may now relocate some of the trees to more suitable locations and replace them with other greenery.
Many locals are upset by the idea. They admire the trees and like the scent, and to some of them an autumn in Hanoi is incomplete without the flower.
Earlier relocations
Moving trees has been tried before. Around 100 blackboard trees were relocated to the outskirts of Hanoi in 2019 because of the smell of their flowers, but a similar plan in 2023 never went ahead after local opposition.
Why does the blackboard tree smell so strong?
The flowers release volatile aromatic compounds that carry far on still air. Many flowers that perfume the evening are pollinated by moths, and the blackboard tree's heavy evening fragrance fits that pattern. Blooming in dense clusters multiplies the effect, so a street lined with mature trees can fill with scent. The tree is an evergreen native to tropical Asia and blooms in the cooler months.
Why is it called the blackboard tree?
Its pale, soft wood was used in parts of South Asia to make school writing boards. The species name scholaris, from the Latin for school, refers to this use. The genus Alstonia was named by the botanist Robert Brown in the early 1800s for the Scottish botanist Charles Alston. The tree also has a milky sap, which is why the local name translates as milk flower.
Why do transplanted mature trees often struggle?
Digging up a large tree removes much of its root system, and roots are what supply water. The tree can suffer transplant shock, with wilting leaves and stalled growth for years afterward. Arborists generally find that survival rates fall as trunk diameter increases. Young trees recover faster because a larger share of their roots comes with them.
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