THERE ARE OPTIONS OTHER THAN THE MORE OBVIOUS DECIDUOUS TREES TO HELP ECHO THOSE LOVELY AUTUMNAL TONES AT HOME
For gardeners with a longing for the autumn gardens of cooler climates, it’s time to head west to Tamborine Mountain, Tenterfield or Toowoomba.
Some locations in the Gold Coast hinterland valleys are also cold enough to induce the changes needed to bring autumn colour.
As the air and soil temperature drops it triggers chemical reactions that induce colour changes in foliage. Cells in leaf attachments break down and foliage starts to fall, leaving the dramatic skeleton of trunk and branches until spring.
Colour changes start with the readsorption of green pigment chlorophyll molecules. These are stored ready to activate buds and restart the photosynthesis process required to manufacture food for the plant through spring and summer.
When chlorophyll is drained away, the remaining colour pigments xanthophyll and carotene are revealed. These are responsible for the bright golden shades, giving leaves their brilliant gold, yellow, orange and rust colours. Buttercup yellow leaves of gingko, the golden poplars and ash, and the rust and gold of oaks.
As chlorophyll is lost from the leaf another chemical reaction creates anthocyanin, the pigment responsible for the vivid reds, scarlets and purples of some species. The brilliant burgundy of claret ash and the deep crimson of Japanese maples, ornamental cherries and some pistachios are the rewarding outcome.
Mixed together in many plants, including persimmon (pictured), all three pigments may result in a kaleidoscope of leaf colour.
Liquidamber will colour reasonably well in milder climates, but is too invasive for anything but the largest gardens. Once their autumn colours would have been a lottery, but plant selection and development of cultivars means colour is a sure thing.
Swamp cypress, a large-spreading conifer, is typically deciduous but some stubbornly refuse to shed leaves. It is also a lucky dip when it comes to autumn colour.
Also only suitable for large gardens, the autumn colours of tropical birch will vary from yellow to a dull brown as it sheds its leaves to reveal a delightful trunk and branches through winter and bring the benefits of a deciduous tree.
Although Gold Coasters can’t rely on colour from the traditional cold-climate autumn trees, they can achieve a wonderful result from crepe myrtles, which are suitable for most gardens.
Many new cultivars of crepe myrtle experience a mild colour change before shedding leaves. Their bark exfoliates as an extra bonus, revealing pale and dark shades and taking on a glistening shine when wet.
There is splendour in a bare-trunked tree with its detailed silhouette of leafless branches. There are also benefits as well as beauty. A bare tree allows sunlight to filter to the ground below, warming the ground in early spring for flowering bulbs.
Deciduous trees also let sunlight reach through windows to brighten and warm buildings. Fallen leaves are a rich supply of nutrients as they break down and are a great addition to the compost heap.
If you’re not sure which deciduous trees will grow locally and are appropriate in size and appearance for your garden, check out the stunning but large swamp cypress, crepe myrtles and grove of tropical birch at the Gold Coast Regional Botanic Gardens.
Kate Heffernan is a horticulturist, educator and honorary life member of Friends of the Gold Coast Regional Botanic Gardens. You can listen to her radio show Garden Talkback on ABC 91.7FM. Details at kateheffernan.com.au