Autumn's here

Jonathan Garner loves this time of year.

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It won't be long before the unsavoury periods of our various climate patterns begin to settle. The heat and dry of the Mediterranean regions begin to cool and receive rain. The humid tropics begin to cool and dry up. The inescapable and draining humidity starts to reduce in my coastal Sydney zone while the autumn colours start showing their beauty in the cooler temperate zones where I prefer to work.

I know very few landscape professionals that enjoy humidity.

Through all of the climate zones, autumn is a transformative season for the plants.

This is most noticeable at the extreme ends of our climate types - by 'extreme ends', I mean the tropics, the cool temperate and the mediterranean climates.

It's a time when plants (and insects) prepare for winter dormancy in the temperate and tropical zones, or adapt to the changes in environmental conditions in other climate areas. It's the time when breathtaking autumn foliage colours can adorn the landscape.

What is autumn colour all about?

The spectacular phenomenon where the leaves of many deciduous trees and shrubs change from greens to vibrant shades of yellows, oranges, reds and purples is the result of complex biological and chemical processes going on in the leaf. The colour change is triggered by shorter daylight hours, cold night temperatures, and to a slightly lesser extent, dry conditions. Most autumn-coloured plants pretty well stick to the same colour or pigment every year. This is due to the inherited colour or genes of the particular cultivar or clone. The intensity of the colour each year is generally due to the environmental factors mentioned earlier.

Chlorophyll. The green stuff

Most plants are green and all plants have a green pigment called chlorophyll. Even burgundy- or purple-coloured plants have chlorophyll. It's just hiding beneath another couple of pigments which I'll touch on in a tick.