Autumn is such a delightful time of year at Sophie’s Patch and while I love all the seasons, this would probably be my favourite! It’s the sunny days, cooler nights, the promise of an end to the dry season in the not-too-distant future, and an ever-changing display of brilliant autumn tones on the leaves of deciduous trees, shrubs and vines. This autumn show is taking place all over southern Australia, but why do the leaves make such a breathtaking display, and why is there such a variation between different trees, and in different areas?

Deciduous trees, shrubs and vines are ones which lose their leaves over winter and come from cooler climates such as Europe, North America, China and ….. I am a big fan of deciduous plants used as part of sustainable home design for their passive cooling and heating effects, keeping homes cool and shady in summer and letting the precious warming sunshine into warm homes in winter. This makes homes more liveable without the use of electricity to cool and heat homes.

So, at this time of year, when it gets colder and days shorter, these deciduous plants prepare to drop their leaves, which is basically their version of hibernation. The chlorophyl in their leaves begins to break down. Chlorophyll is what gives them their green colour, helps photosynthesis happens (converting carbon dioxide, water and sunlight into energy for the plant), and it also acts as sunscreen. The sugars and other nutrients in the leaves are pulled back into the tree to be stored in the trunk and roots, so that the tree can survive in winter when it is not photosynthesising.

So why do some trees go yellow or orange? When the chlorophyll disappears, this unmasks carotenoids which were already there, but can now be seen as golden colours in some trees like elms, golden ash, gingkos or the oranges seen in Japanese elms and Japanese maples.

The red, purple and scarlet colours come from a pigment called anthocyanin. Cold overnight temperatures and shortening days cause its production. It acts as sunscreen within the leaf as the chlorophyll disappears. When a tree is in bright sunlight it produces more anthocyanins to protect itself, and this is why trees in full sun turn more vivid colours than those in the shade. In addition, near-freezing weather, low nutrient levels and other plant stressors seem to trigger increased levels of anthocyanins.

Even though we did get some summer showers, it has been a long dry summer at Sophie’s Patch and the ground is bone dry, so as a result many trees are colouring early, or losing their leaves very quickly. I have two trees of the same variety, Acer ‘Sensation’, planted within around 6m of each other and one is almost bare while the other still has half of its autumnal leaves on it. So why is this? Well even though they are planted nearby, the soil where they are growing is very different. One is growing in my natural soil, which is loamy and has been enriched over the last decade with years of thick pea straw mulch, increasing its organic matter content, and consequently its water holding capacity. The other was planted next to what was the kids’ sandpit for about 10 years, and therefore is growing in sandy soil with little organic matter to act as a sponge and hold onto water. Basically the tree which is more stressed for water loses its leaves before the one which is less water stressed.

If you want to plant a tree with stunning autumn colour, start by driving around your area and observing what trees are looking good in your neighbourhood. Ask any gardener for their favourite autumn trees and they will give you a different list so here are my top 5 trees for autumn colour at Sophie’s Patch, however when choosing any tree I would always suggest that you consider the other features the tree has, from spring blooms, summer foliage, autumn fruits and winter tracery and bark.

pyrus-edgewood-canopies
Pyrus Edgewood canopies colouring Autumn 2020
  1. Ornamental Pears (Pyrus species and cultivars) There are many different forms of these popular, long-lived trees from broad spreading shade trees to narrow upright columns and I grow nine different types in my garden. You can read my blog post about them at https://sophiespatch.com.au/2020/04/20/ornamental-pears/ . In autumn they produce vibrant autumn tones in shades of red, orange, yellow and purple. I also love the fact that they have stunning creamy white blooms in spring, that smother the tree as if snow has fallen, they have glossy attractive leaves over summer and swollen grey hairy buds over winter, which give me hope that spring is on its way.
  2. ‘Sensation’ Box Elder (Acer negundo ‘Sensation’) This tree turns vibrant shades of red and orange in autumn but also has an attractive pink tinge to its green leaves in spring, before ageing green over summer. It forms a round headed attractive shade tree and is reasonably quick growing.
  3. Chinese Pistachia (Pistachia chinensis) This round headed, deciduous tree with ferny green foliage comes into its own in autumn when it turns electric shades of red and orange. Early training when young will ensure a straight leader to above head height. Autumn really is its main season of interest, however it is extremely hardy and drought tolerant once established so definitely worth considering.
  4. Pseudocydonia sinensis (syn. Pseudocydonia oblongata) – False Quince This unusual small tree or large shrub has large leathery green leaves which turn stunning shades in autumn. It can however be semi-evergreen in milder climates. Producing a mass of large single cerise-pink flowers up to 2.5cm across in spring, this tree then develops large egg-shaped, quince-like fruit in autumn. As well as having attractive flowers in spring, autumn colour and fruits, it also has attractive flaky bark, making it another ‘Good Value’ tree.
  5. Washington Thorn (Crataegus phaenopyrum) Even though these trees are only young in my garden, I love them. They survive on rainfall alone with no supplementary watering and still produce stunning autumn foliage, pretty white flowers in springtime, attractive heart-shaped glossy green foliage over summer and a showy crop small red berries in autumn. Ok so they are a thorn, so they are prickly, however this is not a problem if you develop a central leader with the canopy above head height. Just don’t go climbing your tree and think of what great protection these trees for birds building nests!

PS. While I would love to include ‘Indian Summer’ Crepe Myrtles in this list as they do turn shades of orange, scarlet, burgundy and gold in autumn, and they do have amazing flowers for 60-90 days in summer and striking exfoliating bark which is a winter feature, my salty bore water does result in leaf burn and this means that I don’t really get the autumn show.