Scientific: Grevillea robusta
Common: silk oak, Australian silky oak
Family: Proteaceae
Origin: Southeastern Queensland and northeastern New South Wales, Australia.

Invasive Alert: Silk oak shows moderate levels of invasive potenitla in mild climate regions around the world. It has naturalized in South Africa, New Zealand, Hawaii, French Polynesia, Jamaica, Norfolk Island and south Florida.

Pronounciation: Gre-VIL-lee-a row-BUS-ta

Hardiness zones
Sunset
8, 9, 12-24
USDA 9-11

Landscape Use: A skyline tree with strong vertical accent, mesic landscape designs.

Form & Character: Rugged looking evergreen tree, wispy and stately.

Growth Habit: Upright, moderate to fast to 80 feet in coastal central and southern California, typically around 50 feet when mature in Phoenix.

Foliage/Texture: Alternately arranged foliage fern-like to pinnate, entire of lobed, leathery, slow to decompose after abscission; medium to coarse texture depending on tree size.

Flowers & Fruits: Showy orange yellow flowers arranged in one-sided 4 inches long raceme; fruit a leathery follicle.

Seasonal Color: Sometimes spectacular floral display in the spring.

Temperature: Susceptible to trunk sun scald. Needs protection from western sun.

Light: Full sun

Soil: In Phoenix, avoid hot, dry sites. Do not plant near reflective surfaces or on south and west exposures of large buildings.

Watering: Regular

Pruning: Elevate foliar canopy base only as needed.

Propagation: Seed

Disease and pests: Root rot in poorly drained soils.

Additional comments: Silk oak is an ornamental and stately tree for mesic and oasis landscapes in Phoenix that casts a strong skyline silhouette. It is however a relatively messy tree that produces copious leaf and small branch litter. Moreover, silk oak leaves are unusually lignified and decay slowly, which can just compound the litter irritaions of landscape neat freaks. Silk oak was once more frequently planted in Phoenix, but is not today as it doesn't conform to our prevailing present expectations of landscape water conservation and xeriscape.

Silk oak wood from indigenous silk oaks in Australia is a valuable source of timber. Overall, Grevillea itself is a robust genus of over 250 tree and shrub species from Australia.