| Botanic name | Acacia dealbata |
| Other names | Silver wattle, blue wattle, mimosa, mimosa acacia |
| Main Origin | Southeastern Australia |
| Mature size | 4 – 10 m x 5 – 15 m (w x h) |
| Mature form | Shrub or upright tree with rounded canopy |
| Foliage | Ferny, bluish grey or silvery green |
| Growth rate | Fast |
| Position | Full sun, part shade |
| Soil | Prefers fertile, well-drained soils but adapts to other soils |
| Water | Deep watering during extended drought periods |
| Climate | Mediterranean, temperate, subtropical |
| Flower | Bright yellow, spherical, from winter to spring |
| Use | Feature tree, tall screening, avenue planting |
| Notes | Globally widespread |
IN THIS ARTICLE
Overview
Acacia dealbata, commonly known as Silver Wattle, Blue Wattle, or Mimosa, is a stunning, fast-growing, evergreen tree native to southeastern Australia.
Renowned for its bright yellow, fragrant flowers and striking silver-blue foliage, it is a widely cultivated tree in Australia and abroad. It thrives in various climates and soil types, making it a resilient and adaptable species.
Due to its rapid growth, it is often used in reforestation, erosion control, and land rehabilitation projects. However, it has become invasive in many parts of non-native regions.
Origin and distribution
Acacia dealbata grows in dry or wet forests and open woodlands, particularly on hilly slopes, riverbanks, and other places like swamp margins, deep gullies, subalpine areas, and high plateaus in southeastern Australia.
As a highly adaptable species and a prolific seeder, it has become naturalised in parts of South Australia, Western Australia, and overseas in New Zealand, southern Europe, China, India, southern Africa, and America following its introduction.
In many countries, Acacia dealbata has been declared an invasive species. In South Africa and New Zealand, for instance, it is an environmental weed that outcompetes native vegetation. Despite this, its popularity remains high in landscaping and reforestation.
Growth and care
Silver Wattle naturally thrives in cool or warm temperate climates with moderate to high rainfall. It is also highly adaptable to a drier Mediterranean or more humid, mild subtropical climate.
The species can grow into a handsome tree with a staggering height of over 25 meters in wetter regions. However, it is often significantly smaller in cultivation, rarely beyond 15 meters. In drier sites, it can even adopt a shrubby form.
Acacia dealbata grows on a range of soil types in its natural range, from deep, fertile, moderately drained clay soils in forests and watercourses to quickly drained, infertile, sandy or rocky soils on hilly slopes.
The species can flourish in various soils so long as they are slightly acidic to neutral and have adequate drainage.
There are two subspecies of Silver Wattle. The taller Acacia dealbata subsp. dealbata often appears in areas of low to moderate altitudes and can withstand some frost (down to -5°C).
In contrast, Acacia dealbata subsp. subalpina is often smaller (< 5 m) and found in mountainous, alpine regions. This subspecies is more cold-tolerant and can resist frost and snow.
While young trees require regular watering, established Silver Wattle can withstand extended periods of drought. Mulching around the young tree can help retain moisture, facilitating its growth.
While fertilisation is not strictly necessary as Acacia dealbata is a nitrogen fixer, applying organic matter or a low-phosphorus fertiliser can promote healthy growth in nutrient-poor soils.
Features
Acacia dealbata can quickly reach 5 – 15 meters in height or more, depending on the growing conditions, such as moisture availability. It often stays as a small tree or a large shrub in drier regions.
Its overall form is upright and spreading, with a graceful, semi-open structure that gives it a light and airy appearance. The canopy is often semi-open, broad, and rounded, offering a soft visual texture in the landscape.
Its branches are slender and spreading, forming a layered effect that enhances the tree’s ornamental appeal. Young branches are covered in white ‘waxy bloom’, giving them a silvery appearance, especially when contrasted with the surrounding foliage of other tree species.
Its trunk is smooth and greyish when young but becomes darker, rougher, and fissured with age, particularly near the base, giving the tree an ever-changing character.
The most striking feature of the tree is its feathery, bipinnate foliage, which consists of tiny leaflets arranged along the delicate leaf stems. The leaves are distinctive silvery-blue to grey-green, leading to its common name, Silver Wattle.
Magnificent blooms are another key feature of Acacia dealbata. During late winter to early spring, the plant bursts into bloom with masses of bright yellow, fragrant, spherical flowers in large clusters that attract pollinators like birds and bees.
Following the blossoms, seedpods develop. Once fully ripe, the pods split open to release the seeds inside. This plant is a prolific seeder, producing numerous seeds each year, many of which remain viable for decades, enabling the species to spread rapidly.
The prolific seed production, fast growth, and its ability to sucker from roots contribute significantly to its invasiveness that can overwhelm the native vegetation in non-habitat regions.
Nevertheless, Acacia dealbata is a pioneer species that can rapidly colonise disturbed or degraded lands affected by fire, land clearing, or erosion. Its role in forest restoration, land rehabilitation, and erosion control is highly valuable.
FAQs
What is the lifespan of Acacia dealbata?
The lifespan of Acacia dealbata is typically around 20 to 40 years, though this can vary depending on growing conditions and environmental stressors. In ideal conditions, some trees may live slightly longer, but as a fast-growing pioneer species, it tends to have a relatively short lifespan compared to slower-growing hardwood species.
How fast does Silver Wattle grow?
Silver Wattle is known for its rapid growth, especially in its early years. Under favourable conditions, it can grow up to 1 – 2 meters per year, often reaching 6 – 10 meters in just 5 – 7 years.
