Acacia mearnsii | ‘Black Wattle’, ‘Uwatela’ | Seeds
Acacia mearnsii, most commonly known as the ‘Black Wattle’, is a fast-growing Australian tree of the Fabaceae family. Located within the Botrycephalae subgenus, mearnsii is thought to be most closely related to Acacia baileyana, Acacia dealbata and Acacia nanodealbata. Other common names for the ‘Black Wattle’ include ‘Acacia Centenario’, ‘Acacia Noir’, ‘Acácia-negra’, ‘Aromo Negro’, ‘Australian Acacia’, ‘Blue Passionflower’, ‘Gerber-Akazie’, ‘Green Wattle’, ‘Hei Jing’, ‘Late Black Wattle’, ‘Mimosa Vert’, ‘Mosa’, ‘Swartwattel’, ‘Tan Wattle’ and ‘Uwatela’.
Mearnsii is an attractive evergreen spreading tree, ranging from roughly six to twenty or so metres tall and with a lifespan of approximately fifteen to thirty-five years. Its trunk averages ten to thirty-five centimetres in diameter, with smooth to fissured, grey-brown to black-coloured bark. Mearnsii’s densely-packed, bipinnate, leaves ten to twelve centimetres long and are coloured a dull olive-green, while its fragrant flowers are usually cream to pale yellow. The species produces straight or twisted, dark brown to black-coloured seed pods, which grow up to around ten centimetres in length.
First described in 1925 (and named after American naturalist Edgar Alexander Mearns), the species is generally considered to be invasive when allowed to escape controlled cultivation. Nevertheless, it’s a very useful and attractive species which has been introduced to Africa, Asia, Europe, New Zealand, North and South America and the Pacific and Indian Ocean islands. One quality adding to this vigour is that mearnsii is fire-adapted, recovering well where other species may struggle.
Growing in USDA Hardiness Zones 10 and 11 in coastal scrub, disturbed areas and wasteland, forest and woodland, grassland, riparian areas, road sides and savannah, mearnsii is a popular source of commercial charcoal, firewood, tannins and timber. As with other members of the Acacia genus, mearnsii is also used for its nitrogen-fixing and erosion control properties. In nature, these qualities allow the species to play an important part in the regeneration of local ecosystems subsequent to fire. The species enjoys many other uses too; as a much-loved ornamental, in traditional indigenous medicine (for example, to treat diarrhoea and dysentery, haemorrhoids or internal bleeding), as a famine food and for its fibres (to produce paper pulp, rope or string).
The ‘Black Wattle’ is easily and commonly grown from seed (and occasionally via cutting, although this route is much more difficult). As with most Acacia, germination rates are best when seed is pre-treated (they can go dormant but remain viable for up to fifty years stored at ambient temperature). We’ve written a simple beginner’s guide to this process here. Germination rates of around 75% can be expected within two weeks or so, presuming quality of seed and technique.
Mearnsii should be planted deep in moist but well-drained soil, with the species thriving in well-aerated, light-textured, neutral to acid loam. To minimise evaporation and runoff, cover the seeds until germination has occurred. Once the seedlings have formed three or four leaf pairs and are around six centimetres in height, they can be transplanted into containers in partial shade and watered daily. After nine or ten months they can be planted in the ground (or a large container) in partial shade to full sun, to be nurtured through to the mature tree stage. Space them at least ten metres apart if in the ground, to allow them enough space for mature growth.
Everyone should grow an Australian Acacia (or three) – why not start with Acacia mearnsii?!
All the seed sold by Arkham’s Botanical was freshly and ethically sourced in 2018-2019