The red flowering gum, Corymbia ficifolia (formerly Eucalyptus ficifolia) is one of those trees that really grabs your attention when it’s in full flower, like very few other flowering trees can, perhaps with the exception of the jacaranda or the Illawarra flame tree.
However, one of the ongoing problems with the red flowering gum has been that it’s always been grown from seed in the nursery industry in the past. When it did flower, after 5 to 10 years, the colour varied enormously as there is a great deal of genetic variability within this species. Not only does the colour vary, but the height of the tree can vary from a 10-15 metre substantial tree to a mallee form that’s no more than a couple of metres in height – a form which does have its advantages in the smaller gardens of today. One of the exciting developments in horticulture in recent years has been the development of the red flowering gum to make it more predictable and amenable to garden culture.
Before I talk about that, though, I’d like to talk about the botany and the name change from Eucalyptus ficifolia to Corymbia ficifolia. The reason why the group of gums that include the red flowering gum were separated from Eucalyptus were that there are considerable differences. Corymbia are generally known as the bloodwoods and they have a special characteristic of being terminal flowering, with all those big sprays of flowers held on the end of the branches, which can be seen from a very long distance away. Many of what have remained as Eucalyptus flower way back inside the canopy on the axillary buds, unlike the terminal buds of Corymbia. Indeed, many people are surprised to hear that all gums are ‘flowering gums'; the red flowering gum just holds its flowers where they can be easily seen. Corymbia shares this terminal flowering with Angophora, sometimes known as the apple gums, of which the Sydney red gum, Angophora costata is probably the best known in cultivation. The botanists faced the dilemma that Corymbia gums were more closely related to Angophora, both being terminal flowering and sharing some other characteristics. Being closer to Angophora, it was either include everything within the one genus of Eucalyptus, or split off the bloodwoods and create a separate group for them sitting in between Angophora and Eucalyptus.
Which brings me to the genetic improvement of the red flowering gum, a brilliant but unreliable species, in the genetic sense that you don’t know what you’re getting! One of the more amazing projects that I’ve seen in my career as a plant breeder happened up in Queensland. A fellow by the name of Stan Henry, a retired horticulturist, wanted to grow a red flowering gum in his home garden but he was in the humid climate of coastal central Queensland. He watched a number of his Corymbia ficifolia die from the heat and humidity, and from the leaf spot that they tend to get when they’re grown in Sydney and further north (you can grow them but they look very ratty and not a good garden specimen).
The strategy that he then chose was to hybridise Corymbia ficifolia, the red flowering gum from around Albany in south-west Western Australia with the swamp bloodwood, Corymbia ptychocarpa from northern Australia, which has the same spectacular terminal flowers common to all the Corymbias, but is obviously much better equipped to cope with the humidity and heat of northern Australia. By crossing those two species together, we get a group of hybrids which has been marketed as the Summer series – ‘Summer Red’, ‘Summer Beauty’ and ‘Summer Snow’, a white variety. By and large it’s been quite a successful series when planted in gardens up and down the east coast, from Melbourne through to Queensland. Hybridisation is one way to go, and I like to think of what he’s done as a wonderful reconciliation, a sort of ‘east meets west’, between the swamp bloodwood from the east and north east and, from the other corner of the continent right down in the south-west, the red flowering gum. That’s where I think plant breeding really does have a place in modern horticulture; to combine the outstanding features of two different species to come up with a plant that has all the right attributes to be a successful garden plant.
One of the issues with all the selections, whether they’re straight selections of Corymbia ficifolia or hybrids like the Summer series, is that they are difficult to propagate by cuttings – too difficult for commercial production. The way that they’re propagated now is by grafting onto the rootstock of a hardy member of the Corymbia group, such as the spotted gum, Corymbia maculata, or the red bloodwood, Corymbia gummifera. Finding the right species to use as a rootstock for different areas has become one of the key challenges for the selection and improvement of the Corymbia group, and in particular the flowering gums.
The second wave of improvement of the red flowering gum has come about through the selection of different clones of the red flowering gum though the hundred years or so that this plant has been in cultivation. In southern Australia, from Perth across to Melbourne and up the southern coast of NSW, Corymbia ficifolia is quite a reliable species in its own right. Having been grown from seed, there’s all sorts of variation, so various nurseries have selected their outstanding forms of Corymbia ficifolia and we’re now seeing some interesting new cultivars emerge from that work. ‘Wildfire’ is one the oldest selections, and there are new ones called ‘Baby Red’, ‘Baby Orange’ and ‘Calypso’. They’re all slightly different in both flower colour and plant height, so it’s a matter of going out and finding out what is available from your local garden retailer. There will be a continuing series of new selections in the future as we get more confident with the grafting of red flowering gums in its various colour selections and finding the right rootstock partner.
The red flowering gum is one of our most iconic Australian species in cultivation, and through some judicious genetic selection and breeding work, we’re now starting to see cultivars emerge which are going to be more reliable – as far as knowing what flower colour and height you’re going to get. Hopefully in the future, you’ll be able to find anything from a 2 metre shrub to a 15m tree to match your garden requirements. So if you’ve ever planted a seedling tree and been disappointed, have another look as more new colours and forms emerge.
[You can now see how to prune your flowering gum in the new post by Angus How to prune a flowering gum]