The palette of autumn

Autumn’s colours are more than just for show.

Boston ivy garden in autumn. Picture: Simon Griffiths

What is your favourite season? For many Australians it may well be autumn because our summers are so darn hot.

Of course, our autumn doesn’t really start on March 1 – that’s just a calendar date we inherited from a northern hemisphere system. Every year people seem newly surprised that it’s still hot into March. This year was a corker and we should expect our summers to get worse.

Maybe it’s because we’re hanging out for relief that we love autumn. By April we’re noticing the days are much shorter and the sun has lost its sting. There’s a welcome nip in the air at night, making sleep easier. The early mornings feel fresh and clean. It’s invigorating.

In the sub-tropics and tropics the high humidity loosens its sticky grip, while in southern areas that endure dry, hot summers, autumn brings something even more important: the chance of rain.

Cloudehill garden in autumn. Picture Simon Griffiths

Autumn rains facilitate the main planting season and turn brown, dusty lawns green again; parks and pastures are transformed. For all of us, cooler temperatures and warm soil in autumn create ideal conditions for transplanting evergreen shrubs and trees, lifting and dividing perennials, and repairing the ravages of summer.

Nature heralds this glorious transition to autumn by making the trees change colour. Not the evergreens, of course, but the deciduous trees that evolved to survive cold winters by shedding their tender leaves and shutting down in a type of planty hibernation. The theory used to be that the withdrawal of nutrients and green chlorophyll from the leaves allowed the yellow, orange and red pigments – carotenoids and anthocyanins – to show up. These substances help protect the leaves through the year in various ways, but recent research suggests trees actually produce more anthocyanins in autumn to serve as sunscreen while chlorophyll is dismantled.

Boston ivy garden in autumn. Picture: Simon Griffiths

Other theorists suggest there is a role in warding off insect attacks.

For us, the result is a dazzling display of autumn colours, which is best in colder climates. The most intense colours develop with clear sunny days and cold nights; cloudy weather makes for warm nights and so works against colour development.

The best butter yellow display is from the maidenhair tree, Ginkgo biloba, while golden ash (Fraxinus excelsior ‘Aurea’) wears a deeper gold. Claret ash (Fraxinus ‘Raywood’) has the darkest red; Lipstick maple (Acer rubrum ‘October Glory’) glows crimson.

Cloudehill garden in autumn. Picture: Simon Griffiths

Many species cover the spectrum from yellow to orange to red, including dozens of Japanese maple (Acer palmatum) varieties, Chinese pistachio (Pistacia chinensis), tupelo (Nyssa sylvatica) and the underused parrotia (P. persica). For those in warmer climates, the best performers are Chinese tallow (Triadica sebifera), ornamental pears (Pyrus), and in large gardens, liquidambar (L. styraciflua). As always when choosing trees, check they are of appropriate size and shape for the position.

After the show, of course, comes the clean-up. But don’t think of it as mess, rather the most precious yet free material you can add to your compost and turn into nutritious leaf mould. And please do let the children jump into the piles of raked leaves before you cart them away.

Q&A

Can I hard prune our white crepe myrtles? When is best? Jan Phelan, by email

Crepe myrtles will tolerate very hard pruning, best done in winter. Some people do this annually to limit the size of their trees. It’s called pollarding and causes “knuckles” to develop over time at the pruning points. Regrowth in spring is strong and straight, so it does alter (some say spoil) the form of the tree. You can tip prune the regrowth early on to help it bush out. Alternatively, prune to shape the tree straight after flowering.

I heavily pruned a mature 8m-tall white mulberry the last two winters but it keeps coming back higher and wider. How can I contain it better? Don Frayne, Perth

With some plants the harder you prune, the more the growth roars back. Mulberries, bougainvilleas, jacarandas, crepe myrtles and wisteria are among these. Try a lighter prune in summer or early autumn and don’t fertilise it. Morus alba is a large tree that easily grows to 10m, so if you only want a small tree consider replacing it with a dwarf variety.

Why do new hydrangea varieties seem to wilt and the flowers shrivel at the first rays of sun, despite loving care? Old hydrangeas grow huge, thrive on neglect and don’t wilt. Will the new ones become hardy? Sarah Childs, Lithgow, NSW

New varieties can be bred for unique flower form or colours at the expense of toughness. And it’s not surprising that plants taken from the perfect, nurturing conditions of a nursery and thrust into the real world can struggle to adapt. It can take a few seasons for plants to establish thoroughly and adapt to local conditions.

Who Flung Dung

Send your questions to: [e-mail] or Helen Young, PO Box 3098, Willoughby North, NSW 2068. Website: helenyoung.com.au. The best question for March wins two bales of WhoFlungDung mulch, 8kg Gyganic citrus fertiliser, and 1 litre GOGO juice from Neutrog, worth $100. 