Autumn is all about colour as trees that have been green and lush all summer long reveal new and flamboyant personalities. Expect to enjoy flame-coloured leaves on maples, burgundy and red on grapevines and yellow on ash trees while crepe myrtles have their own cascades of yellow and gold.
The plants that put on these amazing leaf colours are deciduous. This means they lose their foliage in autumn or early winter and enter a period of dormancy until spring returns and they regrow their leaves.
The autumn colours are revealed as trees prepare to drop their leaves as a precursor to their period of winter dormancy.
Trees are great recyclers and don’t just throw their leaves away. They recover nutrients from each leaf before they allow them to fall. The changing length of day signals that winter is on its way and triggers deciduous trees to gradually stop producing chlorophyll (the pigment that makes leaves appear green) and begin the process of closing off the leaf so it can be discarded.
Chlorophyll allows leaves to undergo photosynthesis, which is the chemical reaction that uses the energy from the sun to turn carbon dioxide and water into sugars that help the tree grow.
As the chlorophyll and the green colour it produces disappears from the leaf, other colours are revealed. These colours are associated with other pigments present in the leaf.
Carotene, the pigment that’s responsible for the orange colour of carrots, is also found in leaves. Poplars and birch leaves for example have high levels of carotene so these trees reliably develop bright yellow autumn colours.
Another leaf pigment that contributes to autumn colouration is anthocyanin. This pigment is also responsible for the red colour in fruit such as apples, red-tinged peaches and strawberries.
Anthocyanin is formed in some trees in autumn as chlorophyll reduces and the process of retrieving nutrients from the leaf for winter storage begins. Anthocyanin is dissolved by leaf sap where it reacts with sugars in the sap to form tones of red and purple. Trees that produce high levels of anthocyanin include maples, liquidambars, dogwoods and persimmons.
Top plant choices
Join the autumn colour parade by selecting and planting a deciduous tree, shrub or vine over the months ahead. While many of these plants are sold while they are dormant as bare-rooted stock, potted specimens complete with autumn foliage are in stock at garden centres during autumn.
Autumn colour is best in cool, mountain and inland climates and lasts longest after good summer rain. However even in warm and coastal gardens there are plants that can be relied on for a good autumn show including ash (especially claret and golden ash), Chinese tallow, crepe myrtle, American and Japanese maples, ornamental pears and persimmon. Ornamental grapevines also put on a striking autumn display and make an impact when they are trained over a pergola. Even wisterias put on a show of golden leaves and become an attractive feature during autumn.
Complete the picture with autumn-flowering shrubs and perennials including sasanqua camellia, roses and salvia.