Acacia cultriformis aka Knife Acacia

Acacia cultriformis is an evergreen shrub or small tree. Common names include knife acacia and knife-leaf wattle. It belongs to the pea family, Fabaceae. Its native range runs from southeastern Queensland into New South Wales. There it grows on rocky ridges, in dry forests and heath. These habitats lie within a subtropical region of Australia.

In gardens, it reaches 8–13 feet (2.5–4 metres) tall. Its spread is about 5–8 feet (1.5–2.5 metres). Plants take around 10–20 years to reach full size. The form can be upright, bushy, or spreading. Some plants trail or grow close to the ground. Small, triangular, silver-green leaves give the plant its knife-like look. Their blue-grey cast contrasts with the bright flowers. Unlike divided acacia foliage, these leaf-like parts are solid.

Small yellow flowers form round heads in dense clusters. They grow from buds at shoot tips and along stems. Bloom falls in late winter and spring. Chicago Botanic Garden lists January through April as flowering months. The flowers attract butterflies, and growers use this species for honey. Its flowers also yield a yellow dye. The seed pods provide a green dye. Plants For A Future lists cooked flowers as edible. Their pollen-rich blooms can be used in fritters.

Grow it in full sun with shelter from harsh exposure. The soil must drain well but can range from dry to moist. Loam, sand, and chalk are suitable soil types. It accepts neutral soil and slightly acid or alkaline conditions. Salt tolerance makes it useful in coastal gardens. RHS gives it a UK hardiness rating of H3. Chicago Botanic Garden lists USDA zones 9–10 and recommends frost-free conditions. Move young plants to their final site early. This species resents later moves.

Use it as a specimen, hedge, or border plant. It also suits courtyard gardens, sunny walls, banks, and slopes. Root microbes help it gain nitrogen from the air. Raise new plants from seed or semi-ripe cuttings. Watch for red spider mites, fluted scale, and mealybugs. Honey fungus may also cause problems. Plants For A Future reports no known hazards or medicinal uses. That report does not establish safety for every use or animal.