The morning sun rises above the rolling hills of Horton Plains National Park casting a golden glow over the endless stretch of purple, pink and blue flowers. This is the long-awaited bloom of the Strobilanthes flowers that occurs once every few years.

The star of the show, Strobilanthes pulcherrima, known locally as nelu or nillu, only blooms once every 12 years. It belongs to the Strobilanthes genus, which includes about 300 species worldwide. Around 30 of these are found in Sri Lanka, of which 26 are native and found only in Horton Plains in the country’s central highlands.

A designated UNESCO World Heritage Site since 2010, Horton Plains is a distinctive upland region of remarkable biodiversity, encompassing montane grasslands and cloud forest. This year’s bloom, unfolding across September and October, has drawn large numbers of tourists and sparked widespread attention on social media.

Mass bloom

The Strobilanthes are monocarpic plants, meaning that each individual plant flowers only once in its lifetime, produces seeds and then dies.

The first recorded mass bloom was in 1881, observed by Thomas Farr, a British tea planter. Farr later witnessed the bloom again in 1893 and 1905, suggesting a consistent 12-year cycle. In fact, records show that the last major nelu bloom occurred around 2012–13.

Generally, “synchronised flowering” occurs when plants of the same species flower at the same time in the same geographical location. However, in Horton Plains, this remarkable behaviour happens across multiple species, resulting in the rare and spectacular mass bloom.

Why is Strobilanthes important?

After the plants die, they leave behind space for other species to grow and flourish, staying hidden until the next season.

The mass bloom attracts a large number of pollinators, helping maintain genetic diversity while also supporting the ecosystem. Strobilanthes seeds serve as an important food source for birds and other mammals.

These flowers are protected by Sri Lankan law under the Flora and Fauna Protection (Amendment) Act, No. 22 of 2009. This means that destroying, uprooting or transporting these plants is forbidden.

While visitors should enjoy this stunning natural phenomenon, it’s important that it is done responsibly. These flowers are already at risk due to climate change, so people must be careful not to disturb or pick the flora – ensuring that the beauty of Strobilanthes will continue to return for generations to come.