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Small Gums for Small Gardens
The gum tree...
It's as Australian as bush flies in summer and the corks on a swaggie's hat.
The character, the look, the smell of the Australian bush are all due to the gum tree, or eucalypt.
|What's a eucalypt?
|There is some amount of controversy about the botanical naming (taxonomy) of the eucalypts.
There is general agreement that the two genera Eucalyptus and Angophora are closely related - the main difference being the lack of a bud cap (operculum) on the flowers of Angophora. There is also agreement that, within Eucalyptus there are subgroups that are more closely related to Angophora then they are to other species of Eucalyptus.
The bloodwoods form one such group and the cat was thrown among the botanical pigeons in 1995 when a paper was published which separated the bloodwoods and other closely related species from Eucalyptus and put them into a new genus, Corymbia. The debate about the botanical status of the three genera in the eucalypts has raged ever since with some authorities accepting Corymbia as valid and others not accepting it.
The situation was complicated in 2000 with the publication of another paper which combined all three genera into Eucalyptus. That paper, however, has also not received universal acceptance so the situation remains unclear.
At present, the division of the eucalypts into the three genera, Eucalyptus, Corymbia and Angophora appears to be gaining wider acceptance but it will probably take some time before one view or the other prevails.
In the meantime the average enthusiast can take comfort in the fact that they are still all "gum trees"!
It's said that soldiers returning home by ship after the two world wars could smell the aroma of Eucalyptus oil before they could see the Australian coastline on the horizon. Whether this is true or a piece of folklore doesn't really matter; it indicates the affection that most Australians have for the eucalypt. The wattle may be the official national floral emblem, but the gum tree IS Australia.
Of course, the first Europeans to settle in Australia didn't immediately succumb to the charms of the native bush. It was an alien environment and they immediately set about clearing the Eucalyptus "scrub" and re-creating the gardens of their homelands.
The Polish botanist Lhotsky even went so far as to describe eucalypt forests as "mind blunting monotony"....He probably didn't look closely enough. Eucalypt forests and woodlands may look superficially similar between one locality and the next but there is enormous variation between individual Eucalyptus species.
Although the is some debate among botanists about the taxonomny of the eucalypts (see box), for the purposes of this article the eucalypts can be considered as comprising three closely related genera - Eucalyptus, Corymbia and Angophora. Overall there are over 700 different eucalypt species, all but two occurring naturally only in Australia.
Most of these are never seen in gardens and many are probably unsuitable due to their size. The "Mountain Ash" (Eucalyptus regnans), for example, which is found in wet sclerophyll forests of Victoria and Tasmania reaches 70-80 metres. This is clearly excessive for a small suburban garden. But there are numerous smaller species which make ideal subjects. In fact, the gum tree establishes the legitimacy of an Australian garden....it's almost un-Australian to own a garden without at least one, don't you agree! Of course you do!
In selecting suitable small species for smaller gardens there are several factors which need to be considered. Firstly, you need to decide what you mean by "small". Then you need to consider the local growing conditions in comparison to the conditions of the natural habitat of the various species. Many gardeners are attracted by some of the spectacular flowering gums of Western Australia but, in the humid eastern states, these are not usually reliable despite the occasional successful specimen. By the way, the term "flowering gum" is a bit superfluous; all gum trees flower, it's just that some are more spectacular than others.
So what constitutes a "small" gum tree?
For the purpose of this article I have adopted a maximum height of about 10 metres (30 feet) which is achieved in about 10 to 15 years. For the average sized suburban garden this is a reasonable small gum but it may be a bit big if you live on a "handkerchief". That's OK - there are smaller ones for you to consider. It's worth remembering also, that size is fairly arbitrary as local soil and climatic conditions will affect the growth rate as well as the potential height that the tree may reach.
A difficult problem is that many gardeners require that trees be quick growing to a certain height and then stop, more or less. Unfortunately there are few trees that will meet this criterion. Most trees that quickly reach (say) 5 metres are bound for the sky. If you want a tree of more modest ultimate height you will probably have to accept something a little slower in growth rate.
It's also important to realise that most eucalypts are long lived in suitable conditions and even some small ones may eventually exceed 10 metres.
Bark and Trunk Characteristics
All too often floral characteristics govern our selection of plants for the garden. While this is understandable, it's important to remember that once a tree gets to any reasonable size, the trunk (and its bark type) will be one of it's most prominent features unless it's one of those that retain foliage
to near ground level.
Among the eucalypts there are many different types of bark. These include:
- Smooth bark, where the bark is shed annually.
- Stringybark, where the bark is retained in long, fibrous strips.
- Ironbark, where the bark is hard and deeply furrowed.
- Box bark, where the bark is retained as "flakes" which may break away as slabs periodically to leave bare areas.
All of these have their own appeal, although the most popular (and probably the most effective) for gardens are the various smooth barked types. However, the others certainly have their uses.
If you spend a bit of time looking at trees in nature you will generally notice that, in any particular area, there are usually one or two dominant tree species and a few others which are distinctly different. This approach can be applied (albeit on a smaller scale) in gardens.
Placement in the Garden
Trees produce shade.
An obvious statement, I know. But, at planting time, the future impact of the shade that will be produced by a 1 metre sapling is something that many gardeners give only scant attention.
Deciduous trees have always been promoted as being ideal for allowing sunlight to reach living areas during winter while providing a leafy cover to provide shade in summer. But gum trees can do the same job...they just require a little more thought in their placement.
Because the sun is lower in the sky during winter than in summer, placement of a tree to the north of the living areas will allow sunlight to shine below the foliage. Similarly, the foliage will provide summer shade when the sun is overhead. Poor tree location can also adversely affect the performance of shrubs in nearby gardens. Quite apart from the fact that trees may rob gardens of adequate moisture, the shade produced may cause poor flowering of the shrubs, most of which flower better in sunlight. Placement of trees to the south of gardens will minimize this problem.
Another aspect of tree placement is the potential effect on underground pipes and on concrete paths and house foundations. Remember that although I'm discussing small trees here, they are still large plants and the roots of most will find their way into sewer and drainage pipes if given half a chance. As a general rule it's a good idea to plant at least 4 metres away from pipes and from concrete structures as well.
A trap to be avoided at all costs is the temptation to plant trees as specimens widely spaced around the garden. The danger here is that, eventually, the spreading crowns may merge to cast shade over much of the property, including the house.
Trees are much more effective, in both practical and aesthetic terms, if they are grouped rather than spread out. After all, that's how they occur in nature.
You can safely plant most trees within 1.5 to 2.5 metres of each other. In this way, the merging crowns will not cast excessive shade. In the extreme case, it's possible to get an interesting "multi-trunked" effect by planting two or three trees in the same hole.
Incidentally, the multi-trunked "mallee" species rarely adopt that type of growth under cultivation. So close planting of several small gums of the same species is a way to "cheat"... go on, who's to know?
In recent years a number of grafted eucalypts have become available through nurseries. These are generally expensive but they have two important advantages:
- special colour forms can be guaranteed, thus overcoming the colour variations that seedlings can produce
- the range over which plants can be cultivated is increased - for example, by grafting the red flowering gum onto a hardy root stock, this spectacular plant can be grown more reliably in humid eastern areas of the country.
Two recent grafted introductions from Tarrawood Nursery, near Bega on the New South Wales' South Coast show great potential for small gardens. Corymbia ficifolia 'Dwarf Orange' and 'Dwarf Crimson" are claimed to grow to about 3 metres tall by 3 metres wide. Ideal for the smallest garden! These forms have been selected from mature trees growing in the Grampians in Victoria ('Dwarf Orange') and in Bega ('Dwarf Crimson').
The only uncertainty of grafted eucalypts is the long term viability of the graft. These plants have not really being available for long enough for this to be fully assessed. Indications are that they will produce many years of spectacular flowering and are more than likely to satisfy the expectations of most gardeners.
Small eucalypts for your garden
The accompanying table lists 20 or so eucalypts which are worth growing in gardens. Note, however, that not all will succeed in all districts so, in making your selection, try to choose those that grow naturally in your area (or in a similar climate). The table indicates the natural distribution of each plant. As mentioned previously, growers in humid, eastern areas should be particularly wary of the western species unless they are grafted (see box).
Most specialist native plant nurseries will stock species suitable for local gardens and, if you're keen to grow a particular species, you could always try raising your own from seed. Gum trees are generally quite easily raised in this way and, in fact, growing from seed is the way most eucalypts are propagated as propagation from cuttings is extremely difficult. The only problem that can arise is that seedlings can vary in some ways from the parent plant. For example, the red flowering gum (Corymbia ficifolia) may produce a percentage of plants with white or pink flowers.
Whatever you do, have at least one gum tree in your garden. So what if they drop a few leaves on the lawn or in the pool. Until you've sat watching rain running down the trunk of a smooth-barked gum tree, you haven't experienced one of life's true pleasures.
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Australian Plants online - September 2003
Association of Societies for Growing Australian Plants