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27 Apr 2018

Why do leaves change colour?

Even though we are currently in the middle of autumn, the weather has been a little confusing, not yet requiring our usual, snuggly autumnal attire. And we aren’t the only ones confused by the weather, looking around it’s immediately apparent that the trees are also at a loss as to what they should be wearing.

You could be forgiven in thinking that it was Spring, as all the trees remain a sunny green colour.


Autumn colour, which is generally at its most vibrant at Mount Tomah in late April, is caused by chemical changes in the leaves of deciduous trees. As the temperatures fall and days become shorter, less light is available to the plant and chlorophyll production (the green pigment in a plant’s leaves) dwindles and eventually breaks down. Once the chlorophyll has deteriorated, pigments present in the leaf are revealed, such as carotene.

Above is what you would expect to see from the Blue Mountains Botanic Garden Mount Tomah at this time of year. 


Carotene is the pigment which gives carrots their orange hue and autumn leaves their yellow appearance. Meanwhile, the reds we see in spectacular autumn foliage are created by the reaction of the last of the sugars created by the chlorophyll with proteins in the cell sap, resulting in a purply-red pigment called anthocyanin. The production of this pigment requires specific environmental conditions, including lots of sunlight, cool temperatures slightly above freezing and low rainfall.

Unfortunately, with such unseasonably warm weather, we are seeing far less of these red and purple pigments and just a glimpse of some yellows. And while it’s easy to lament that we aren’t seeing the autumn colours of last year, it is an opportunity to stand back and appreciate how little control we have over nature and how it can continue to surprise us.

Although there are less trees changing colour there are some, like this Fraxinus excelsior, who have got the memo.


There is still plenty of colour to see at the Blue Mountains Botanic Garden Mount Tomah, the Proteas are putting on a lovely display, there’s beautiful pink and white Nerines, Cyclamen and Begonias in the Formal Garden and there are Chrysanthemums and Dahlias blooming too. Traditional autumn colour can be seen around the bottom of The Residence and near the North American Woodland.

The Formal Gardens are still filled with colour this April. 


We’d love to see and hear all about your visit to the Garden, so be sure to tag us on Instagram or Twitter.

Images in this blog supplied by Greg Bourke and Megan Harvey
Category: News
Tags: autumn
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