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1 Nov 2022

Damp delay on Jac's purple parade

We are officially in November, the sun is shining, birds are chirping, and the flora is in peak bloom…well, except for the Jacaranda (Jacaranda mimosifolia). This famous tree, native to Argentina and Bolivia and famous for its bright purple hues and fragrant rich lavender blooms, is still mostly in bud despite being in its peak traditional blooming period.

Dr Russell Barrett is a Research Scientist at the Australian Institute of Botanical Science. He specialises in discovering, documenting and protecting Australian flora but has a keen interest in plants around the world, having seen Jacarandas in their natural environment during a trip to South America.
"Flowering of Jacarandas has been delayed for at least two weeks this year as they respond to a number of environment factors," Dr Barrett said. 
Dr Barrett

Temperature and rainfall

It is no surprise that the flowering period was delayed this year with September’s record rainfall reaching the fifth wettest month on record for Australia and over twice the national average in comparison to September 2012, which was well below the historical average. 

This record rainfall directly coincides with more cloud cover, which artificially reduces the length of the days, resulting in Jacaranda trees thinking it is earlier in the year since the average temperatures are also lower.

These significant climate shifts have left researchers like Dr Barrett guessing how delayed the flowering period will be this year.

“So far, only a minority of Jacaranda trees are in flower, with most trees still in bud or with only a few flowers,” Dr Barrett said.

“This is not for a lack of flower buds through as most trees are bursting with buds from the record rains, so this Jacaranda season promises to be spectacular once it arrives,” he said.

Rain pours down on the Sydney Opera House on October 6, 2022. (Photo by Muhammad FAROOQ / AFP) (Photo by MUHAMMAD FAROOQ/AFP via Getty Images

Emergence of flowers 

These famous trees have unique prominent purple flowers, traditionally putting on their best show from late October – early to November and Dr Barrett suggests these trees, widely known for their beauty, can contribute to our understanding of how plants are affected by climate change.

Jacarandas are quite resilient to various changes in climate as they come from a naturally arid area with a short rain season. But being a popular street tree, the effect of a changing climate is visually evident since the tree is bare for before they come into bloom.  

"The Jacaranda is very useful to track how climate change has affected flowering times in plants since it usually has a very defined flowering period," he said. 

What history suggests 

The first flowering Jacarandas in Australia date back to 150 years ago, when they would commonly flower in December, rather than late October. 

But what has caused today's earlier flowering? This gradual shift has been documented by a study in Johannesburg South Africa where scientists conducted in-depth research using newsletter clippings of flowering seasons dating back to the 1800s to see how temperature has affected the flowering period.

Overall, the study shows the shift in flowering time over those 150 years is directly correlated with a gradual increase in temperature over that same timeframe. 

Visit the historic Jacarandas at The Royal Botanic Garden Sydney

Although now is the time we are meant to be seeing mass displays of purple lining the streets of Sydney, the Jacarandas are playing hard to get, while also providing scientists with significant warning signs about how climate change is affecting Australia’s flora.

Keep an eye out for when they will be in full bloom and visit our very own iconic Jacaranda tree located near Farm Cove at the Garden, with its beautiful backdrop of the harbour and Sydney Opera House.

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