The knife-leaf wattle
Wattles belong to the genus Acacia, of which there are 1350 species world-wide. An iconic part of the Australia bush, the nearly 1000 indigenous species make up the largest genus of vascular plants in this country. They are represented as trees, shrubs and ground covers and are found in a diverse range of ecosystems from rainforests to deserts and coastal dunes. In many regions, such as south-east Queensland, at any time of the year, there will be one or more of these species in flower providing food for both insects and small, insect-eating birds, such as wrens and thornbills.
The knife-leaf wattle (Acacia cultriformis) is a particularly popular species in cultivation. It is a fast-growing shrub native to Queensland and NSW that forms a large, rounded shape approximately 2.5m tall by 2m wide. This shape, which can be maintained by pruning, makes it a very attractive specimen plant for the garden. The knife-leaf wattle is grown as much for it triangular, blue-grey ‘leaves’ as its deep, golden globular clusters of flowers from late winter to late spring. Both are valued in floral arrangements. The flowers are edible and have been used in making fritters. For those interested in plant dyes, a yellow dye can be extracted from the flowers whilst the seed pods produce a green dye.
Like most wattles, the mature plant replaces its true leaves with leaf-like flattened stems called phyllodes. This is an adaptation of the plant to reduce evaporative water loss, allowing it to grow in relatively dry conditions. It has non-invasive roots that are useful in erosion control. As with all members of its genus, the roots contain no
dules that harbour nitrogen-fixing bacteria which improve soil nutrients, and thus make these plants significant pioneer species in revegetation.
The knife-leaf wattle is a hardy plant that is, when mature, frost-hardy and drought tolerant. It requires a well-drained soil and grows best in full sun or light shade. When young, watering in dry conditions and mulching are recommended. The plant will benefit from a feed of slow-release fertiliser for native plants in spring.