Stone Wall Trees of Hong Kong

Walk through the older streets of Hong Kong Island, and you will notice something strange. Big, full-grown trees stand on vertical stone walls, with roots hanging down the masonry like thick ropes. These are Hong Kong’s stone wall trees, and nobody planned them.

A stone wall tree on the old retaining wall at Forbes Street, near Davis Street, in Kennedy Town.

The story starts with the walls. From roughly 1850 until the mid-twentieth century, builders cut flat terraces into the steep hillsides and held them up with granite retaining walls. Chinese stonemasons did much of the work. Many of these walls were laid with little mortar, and what mortar there was crumbled with age. That left small gaps between the blocks, with damp soil packed behind them.

Birds did the rest. Most wall trees are Chinese banyans (Ficus microcarpa), a type of strangler fig. A bird eats the fruit, drops a seed on the wall, and if that seed lands in a damp crack, it can sprout without any ground soil. The roots grow down the face, thicken, and push into the joints and the earth behind them. Researchers at the University of Hong Kong have studied this kind of spontaneous growth, and work from the Education University of Hong Kong shows that strangler figs dominate these old walls. No one ever planted or watered them.

A commonly cited count puts the number at 1,275 trees on 504 walls, with 110 of those walls in the Central and Western District. Some of the trees are huge. One well-documented banyan reached about 21 metres on a wall that is more than a century old. You can see them in two places: Forbes Street in Kennedy Town and Hospital Road.

The relationship between tree and wall is not always friendly. Roots can bind loose stone together, but they can also pry blocks apart. In July 2015, a banyan on Bonham Road fell across two lanes of traffic. That raised an argument about whether such trees should be cut down or reinforced, which the South China Morning Post covered at the time. The government has since published guidelines on tree risk assessment and management.

These trees are rare in cities. For another unusual urban tree story, see our post on the Meiji Jingu Gaien Ginkgo Avenue in Tokyo, or read about the Rainbow Eucalyptus (replace with the exact post URL).

Image Credit: Wikimedia Commons

Banyan roots on the old retaining wall at the corner of Forbes Street and Davis Street in Kennedy Town, photographed in the evening, August 2024.

Image Credit: Wikimedia Commons

Roots of a tree that grows on a stone wall wind through the joints of the old granite wall on Forbes Street in Kennedy Town.

Image Credit: Wikimedia Commons

Aerial roots of a Chinese banyan run down the face of an old retaining wall in Kennedy Town, one of the best-known sites for stone wall trees in Hong Kong.

Image Credit: Wikimedia Commons

The old retaining wall on Forbes Street in Kennedy Town is one of the best-known places to see stone wall trees in Hong Kong.

Image Credit: Wikimedia Commons

Conclusion

Hong Kong’s stone wall trees formed by accident. Old walls, damp soil, hungry birds, and a tough fig species all came together by chance. Most of them are now around a century old. They are part of the city’s ecology and its streetscape, and they show how quickly nature takes over human structures.

References & Sources

• Wikipedia, Stone wall trees in Hong Kong
• Physical Geography (2008), Urban biogeographical analysis of spontaneous tree growth on stone retaining walls
• Education: University of Hong Kong, Old masonry walls as ruderal habitats
• The Willowherb Review, The Stone Wall Trees of Hong Kong
• South China Morning Post, Why Hong Kong’s urban trees need managing better
• Government of Hong Kong, Tree Risk Assessment guidelines paper