What’s what with wattles
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Acacia is a large genus with around 700–1200 species, depending on which authority you consult and how they view the idea of reclassifying the Australian acacias in a new genus - Racosperma. Anyhow, for now we'll consider them all to be acacias and say that the genus includes shrubs, trees and vines, the majority of them are native to Australia, with others are found through Polynesia, Asia, the Middle East, Africa and the Americas. Outside their home countries it's very rare to see a non-Australian acacia in cultivation, though doubtless someone must be growing a few.
Australian acacias are generally known as wattles. They occur in all but the very driest areas of that country and are almost as typical of the native flora as the eucalypts. Indeed, Australians may regard them as more typical, as they even have a Wattle Day (1 September) and the national colours are supposedly derived from the colours of the Golden Wattle (A. pycnantha). That’s appropriate because all but one Australian species (A. purpureapetala) have yellow or, more rarely, white flowers. The flowers are filamentous, often borne in clusters and may be ball-shaped or cylindrical.
The name wattle pre-dates the discovery of Australia and was originally used to describe an adobe-like construction technique — wattle and daub — in which daub (mud) walls were reinforced with wattle (poles interlaced with twigs). When this type of construction was transferred to Australia the plant commonly used became known as black wattle. In fact, it was not an acacia at all but a related plant, Callicoma serratifolia, but no matter, it wasn’t long before it and all the Australian acacias were known as wattles.
Apart from their now rather limited use as a material for primitive construction, wattles have other commercial uses. The seeds are sometimes ground and used as an ice-cream flavouring and the gum as an emulsifier. Blackwood (A. melanoxylon) timber has many uses, as does the timber of the Hawaiian species A. koa. The bark of A. mearnsii is important to the tanning industry. And of course, wattle’s rapid growth makes it an important fuel.
From the smallest shrubs to the stateliest trees, wattles all share one vitally important characteristic: they are legumes. This means that they can survive in poor soils because their roots, with assistance from bacteria, have the ability to extract nitrogen from the atmosphere. As with some other legumes, this may be what gives the roots their rather peculiar smell, a characteristic that anyone digging out a wattle or transplanting seedlings is sure to notice.
In common with the eucalypts, wattle foliage often changes considerably as the plants mature. The seedlings have ferny bipinnate foliage that is retained throughout their lives by some species, such as the common Cootamundra wattle. However, many wattles quickly lose their juvenile leaves and when mature do not have true leaves, but enlarged leaf-like petioles known as phyllodes.
Cultivation
Provided you choose those hardy enough for your climate, wattles are easy to grow in any sunny position with well-drained soil. Most are fairly quick-growing and inclined to be short-lived, especially in good soil. While they may be slower to establish in poor sandy soil, under such conditions you can expect up to three times the usual 10–12 year life of the average garden specimen. As a rule, the small shrubby species and the tall trees, such as the blackwood, are longer lived than the quick-growing medium sized trees.
Acacias are prone to attack by three main pests. Often, small aphids smother the new growth. These aphids not only suck the sap and debilitate the plants, they also excrete a honeydew on which sooty mould may become established. Although it’s not too difficult to spray young trees to control the aphids, in most cases the trees eventually become too large to spray and have to be left to fend for themselves.
Leaf miners frequently attack the foliage, especially the new growth. They seem to be more common on the species with sickle-shaped phyllodes, such as A. floribunda and A. longifolia.
With age, many wattles become covered in large brown galls. They result from damage caused by a fungus, Uromycladium, the first sign of which is an orange rust deposit on the foliage. Caught early, Uromycladium can be controlled by fungicides but the galls are difficult to eradicate and if a plant becomes very heavily infested, its complete removal is usually the only solution.
Propagation
Many wattles are among the pioneer plants that quickly colonise freshly exposed soil or areas ravaged by bushfires. The seeds often have a very long viability period and may remain in the soil ungerminated until just the right conditions prevail.
The seeds, which are rather like small black beans, are the usual method of propagation. You can harvest the seeds yourself — wait until the seed pods are dry and about to burst — or, if you’re looking for more unusual species, consult shrub and tree seed suppliers’ catalogues.
A hard seed coat is one of the features that enable acacia seed to remain viable for long periods. The seed germinates freely in warm moist conditions, but often you have first to soften the seed coat. Although the seed coat helps the seed survive bushfires, there’s no need to burn or smoke the seed. An overnight soaking in warm water usually sufficiently softens the seed coat.
The seed can be sown in trays of potting mix or sprouted on moist paper towels in an airing cupboard. Because the seedlings resent disturbance, prick them out in individual pots as soon as they’re can be safely handled. The stems are usually pretty tough and less likely to be damaged than the roots.
Although some wattles can be grown from cuttings, it’s seldom a very successful method without commercial propagation equipment.
Commonly available wattles
The following are just a few of the more common species, those you’re likely to see for sale in nurseries and garden centres as ready-grown plants. They all tolerate occasional –7°C unless stated otherwise.
Acacia baileyana
Cootamundra wattle
Probably the most widely cultivated wattle, this tree is up to 10 m tall and is native to New South Wales. It is valued for its blue-green foliage and its masses of bright yellow flowers that open from around mid-winter in mild areas, spring elsewhere. ‘Purpurea’ or A. baileyana var. purpurea is a form with purple new growth.
Acacia cardiophyllodes (syn. A. cardiophylla)
Wyalong or West Wyalong wattle
This species from New South Wales is a large shrub up to 3 m tall. Wyalong wattle has light green ferny leaves and bright yellow ball-shaped flowers in spring.
Acacia cultriformis
Knife-leaf wattle
Although similar to A. pravissima, this shrub from New South Wales and Queensland is smaller (2–3 m high × 2 m wide) and is recognisable by its light silver-grey triangular phyllodes. They are densely packed along the stems and are shaped like small knife blades. The flowers are a light golden yellow and open in spring.
Acacia dealbata (syn. A. decurrens var. dealbata)
Silver wattle
As you might expect, the silver wattle of southeastern Australia has silver-grey foliage, of the bipinnate type. It is usually seen as a tree up to 30 m tall but may be kept trimmed to 8 m if necessary. It flowers heavily in spring. Although some forms have cream flowers, most often the blooms are bright yellow.
Acacia deanei
Deane’s wattle
This large shrub or small tree from Victoria and New South Wales has grey-green bipinnate foliage and creamy yellow flowers. It mainly blooms from late summer but has a few flowers through most of the year and is drought tolerant once established.
Acacia decurrens
Early black or green wattle
Very like A. dealbata, which used to be regarded as a variety of A. decurrens, this very upright tree from Queensland and New South Wales grows to 15 m tall. The main difference between it and the silver wattle is that its foliage is dark green. The trunk is also greenish. It produces golden yellow flowers in spring.
Acacia elata
Cedar wattle
Cedar wattle is up to 20 m tall in its eastern Australian homeland and has bright green to slightly grey-green ferny leaves with large sprays of very fragrant cream flowers from spring. It appears to be hardy to at least –5°C and is one of the longer-lived species.
Acacia floribunda
Sallow, gossamer or sally wattle
A large shrub or small tree up to about 6 m tall with fine whippy stems and a willowy growth habit that make it ideal for quick shelter or screening. The phyllodes are long and narrow and it produces mildly scented cream flowers in spring. The sallow wattle is found in southeastern Australia.
Acacia gracilifolia
Graceful wattle
As the name graceful wattle implies, this South Australian species has a soft billowing growth habit. The stems are very narrow and weep slightly under the weight of long, almost needle-like, deep green phyllodes and bright yellow flowers.
Acacia iteaphylla
This 5 m high shrub from South Australia is similar to the graceful wattle in growth habit but differs in having grey-green foliage and pale yellow flowers. It blooms in late winter and often repeats with a burst of flower in the autumn. The flowers are followed by long seed pods. This species withstands trimming and may be used as a hedge.
Acacia longifolia
Sydney golden wattle
Usually densely foliaged, this large shrub or small tree from New South Wales and Victoria grows to around 6 m tall. It has bright green 15 cm long sickle-shaped phyllodes and bears bright yellow flower spikes in spring. This species has been used as a street tree, but with only limited success as its brittle branches break in strong winds. It is also rather prone to attacks by leaf miners.
Acacia mearnsii
Late Black Wattle
This spring- to summer-flowering evergreen tree from eastern and southern Australia has fine, ferny, grey-green foliage. It has an erect habit, grows to around 10m tall and the flowers have a strong and very pleasant spicy scent.
Acacia melanoxylon
Blackwood
In many areas the Blackwood has been planted as potential timber trees. It is a 30 m tall tree found over all of southeastern Australia including Tasmania, and although its wood is beautifully grained it has a reputation for being prone to borer damage. Unlike most acacias, which usually have thin greenish bark, blackwood has thick, heavily furrowed dark brown bark. It has bright green 15 cm long phyllodes and rather inconspicuous cream ball-shaped flowers in spring.
Acacia neriifolia
Oleander-leafed wattle, white wattle
Native to the drier areas of eastern Australia, this late winter- to spring-flowering evergreen shrub or small tree grows to around 8 m tall and has sickle-shaped adult foliage that can be used as fodder. The flower colour ranges from cream to bright yellow. The trunks of young trees are often an attractive silvery-grey.
Acacia podalyriifolia
Queensland silver wattle
Any visitor to Queensland in late winter could hardly miss this large shrub or rangy small tree. Its relatively large bright silver grey phyllodes and yellow ball-shaped flowers stand out clearly among the other shrubs. Despite being a Queensland native it will take occasional frosts to -5°C.
Acacia pravissima
Ovens or alpine wattle
This widespreading 6 m high shrub is one of the most widely grown species and among the hardiest, as you would expect for a species from what passes for mountains in southeastern Australia. Its somewhat weeping branches are clothed in deep grey-green triangular phyllodes and in spring it becomes a mass of mildly scented yellow flowers. The long sprays of beige buds are a showy feature from late autumn.
Acacia pycnantha
Golden wattle
While usually seen as a large shrub, the golden wattle can reach 10 m tall. Found throughout most of southeastern Australia, it has deep green sickle-shaped leaves and relatively large rounded golden yellow flowers in spring. Despite its revered status as Australia’s national floral symbol, this species’ rapid growth has led to it becoming a weed in South Africa.
Acacia riceana
Rice’s wattle
Considering its completely different appearance it’s hard to understand how this plant is often confused in cultivation with A. verticillata. It’s a Tasmanian species that develops into a large shrub or small tree. The phyllodes are deep green, rather leathery and rounded, with bronze winter tints and the cream flowers open in spring. This species tolerates more shade than most acacias.
Acacia rubida
Red-stemmed wattle
This upright open-growing shrub, which sometimes becomes a small tree, has sickle-shaped mid green leaves but appears reluctant to fully dispense with its pinnate juvenile foliage, patches of which sometimes sprout on mature specimens. The foliage of young plants is often red-tinted as are the older stems of mature plants. It is native to southeastern Australia and bears bright yellow flowers in spring.
Acacia sophorae
Coastal wattle
Found mainly in coastal areas of New South Wales where it is one of the most common plants, this species is usually a large shrub, though it can become a small tree. Its phyllodes are narrow and up to 10 cm long, and the bright yellow flowers open in spring.
Acacia verticillata
Prickly Moses
A shrub from southeastern Australia, including Tasmania, that differs from most wattles in having fine bright to dark green needle-like foliage, often with a bronze tint. The dense foliage and wiry branches allow it to be trimmed as a hedge and it has small fluffy cream to soft yellow flowers in spring. The cultivar sold as ‘Rewa’ appears little different from the species.
Acacia vestita
Hairy wattle, weeping boree
This graceful weeping shrub from New South Wales grows to around 3 m tall by 5 m wide and has triangular phyllodes and clusters of tiny, golden, ball-shaped flowers in spring. Considering its hardiness, ease of cultivation (try it for hedging) and beauty, it’s surprising that A. vestita is not more widely grown.
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Seeds of many of the acacia species are readily available from seed merchants that specialise in trees and shrubs and are generally fairly cheap. Those who are keen to try some of the less common species should consult a good reference, such as the two-volume Acacias of Australia by M. Simmons, to decide which would be most worth trying.
Copyright Geoff Bryant
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