Grevillea robusta aka Australian Silky Oak

Grevillea robusta has the common name silky oak. It belongs to the Proteaceae family. Its native range lies in eastern Australia. It spans southeast Queensland to northeast New South Wales. The tree grows in rainforests, including those beside rivers. It also grows in forests on valley slopes. This tree grows fast and keeps its leaves year-round. It has a straight, thick trunk. Young trees have a cone-shaped crown, or leafy top. Older trees have broad tops with heavy limbs that spread.

Garden trees reach about 40–82 feet [12–25 metres] tall. Their spread is often 25–30 feet [7.6–9.1 metres]. Sources report larger trees reaching 115 feet [35 metres]. Wild trees can reach 165 feet [50 metres]. In cool regions, gardeners also grow it for seasonal leaf growth. These bushy plants can reach 10 feet [3 metres]. The bark is gray or light brown. Linked grooves form in the bark as it ages. The leaves grow in an alternate pattern along the stems. They are pinnate, with parts arranged like a feather. This gives the crown a fern-like look. The leaves have green tops and pale, silky undersides.

Mature trees bear yellow to orange flowers in spring. Flowers line one side of each raceme, or flower stalk. Their long styles stick out from the flower groups. The tree blooms well in subtropical regions. It blooms less well in lowland tropical sites. Birds, fruit bats, and bees visit and pollinate the flowers. Dry seed capsules with a leathery feel follow the flowers. These turn silver-gray to brown. Heavy spring leaf fall can leave litter beneath the tree. Leaves also fall at other times of year.

Grow this tree in full sun and soil that drains well. It copes well with heat and drought when grown outdoors. It accepts sand, loam, and clay but grows best in sandy soil. RHS favors acid to neutral soil and a frost-free site. Its UK rating is H2. Florida guidance gives USDA zones 9b–11. Oregon State lists zone 8, reporting greater cold tolerance. In cooler climates, grow it in pots or a greenhouse. Indoor plants may need pruning to keep their size in check.

Silky oak gives shade and suits large, open sites. Its wood provides timber for joinery and furniture, plus fuel. Leaves yield yellow and green dyes. Brittle limbs can break in strong winds. This makes sites near houses unsuitable. Caterpillars may feed on it, though pests cause few problems overall. Wet soil that drains poorly can lead to root rot. It is weedy in parts of Hawaii. PFAF lists the nectar as edible, but other sources warn of clear hazards. Leaves and sawdust can cause skin reactions in people. RHS also warns of skin reactions in pets. Flower buds, fruit, and seeds contain compounds that can release cyanide.