It sneaks up on you – autumn that is. I was paving a client’s front courtyard last week, when I saw a deep red coloured leaf fall from an ornamental pear tree. My initial thought was ‘bit early, its still hot’, but then I realised that it is in fact late march, and that autumn has well and truly arrived.
This then got me thinking about the lovely deep red colours that the leaves turn in autumn. Why is it that they turn such a nice appealing colour? All I could recall about the subject from my time at landscape school, was that it had something to do with the cold weather. The colder the climate the nicer deeper colours the leaves turn. Leaves in warmer climates, such as Sydney, turn paper bag brown before they fall. So I decided to consult encyclopedia Google, and a quick overview of what I discovered is as follows.
A healthy green growing leaf, contains an abundance of chloryphyll. Leaves that contain chlorophyll will always appear green. Light is needed to produce chloryphyll. As the days shorten in the autumn months, the production of chloryphyll reduces.
At the same time as chlorophyll production is reducing, there is an increased production of Anthocyanin pigments. Leaves containing primarily anthocyanins will appear red. Carotenoids are another type of pigment found in some leaves. Carotenoid and Anthocynanin production is not dependent on light, so levels aren’t diminished by shortened days. Carotenoids can be orange, yellow, or red, but most of these pigments found in leaves are yellow. Leaves with good amounts of both anthocyanins and carotenoids will appear orange.
Temperature does affect the rate at which these chemical reactions take place, so does play some part in leaf colour.