Acacia melanoxylon

The Acacia melanoxylon, or blackwood, is an Australian tree with dark green-blue, evergreen leaves. In spring, it produces numerous sulphur-yellow flowers in "balls", which stand out well against the foliage. It will bring an exotic touch to your flower beds, provided you live in a region with a mild climate, as its hardiness will not exceed -6°C (21.2 °F) even once established. This tree appreciates moist soils, even slightly chalky but light and well-draining.

The blackwood is a tall tree that can be found in the coastal forests of Eastern Australia and the high-altitude forests of Tasmania. It belongs to the Fabaceae family (like beans, wisteria...), and is a close relative of the famous florist's mimosa (Acacia dealbata), which is highly appreciated for its fragrance and extensively planted in mild regions. It was introduced to Great Britain in 1808, and then to France around 1835. When juvenile, the blackwood acacia has very fine and divided leaves, with very small, persistent, delicate green-blue leaflets. The mature branches produce different leaves, entire and slightly darker green. These mature leaves are actually phyllodes, meaning flattened petioles without a lamina, which perform the chlorophyll function of the plant. The two types of leaves often coexist on growing specimens. Between March and June, depending on the region, this tree produces numerous flowers grouped in small "balls" (glomerules), slightly fragrant, with a beautiful sulphur-yellow colour that contrasts with the dark green foliage. They are followed by decorative brownish-yellow pods containing small black seeds (inedible for humans). While it can reach 30m (98ft) in its natural habitat, it will not exceed 15m (49ft) in our latitudes, with a spread of 5 to 7m (16 to 23ft). As its other name "hardwood acacia" suggests, this species produces dense and dark wood of very good quality, which is highly valued in cabinetmaking and carpentry. The trunk is dark beige when young, then darkens and becomes scaly over time.

Cultivating Acacia melanoxylon is not very difficult: it enjoys sunlight and will thrive in any light, moist, well-draining neutral soil that does not dry out in summer. Its tolerance to limestone makes it an appreciated grafting stock for lime-hating species. However, like all mimosa trees, it is quite sensitive to cold. This species remains one of the most resistant, as it can tolerate -5°C (23°F) while young, and then -10°C (14°F) once well established, possibly more in very good conditions. Be aware that young branches and leaves are susceptible to late frosts, and it is imperative to plant the tree in a location sheltered from cold winds. It produces weak suckers, less than its cousin Acacia dealbata which allows for propagation of the plant.

The blackwood mimosa brings a pronounced exotic touch and, in mild climates, it will make a sensation alongside other plants from the oceanic regions such as Grevillea, Callistemon, or the superb Tristaniopsis laurina.