Grevillea robusta (Silk Oak)






Grevillea robusta (Silk Oak) tree

Grevillea robusta (Silk Oak) tree

Grevillea robusta (Silk Oak). Zones 9-12, Sunset 8,9, 12-24. Evergreen tall tree native to Australia, pyramidal at young age with more pronounced big limbs and somewhat widened crown at maturity 50-60 ft tall x 25-30 ft wide can reach 100 ft x 50 ft wide. Great fast growing shade/ornamental specimen tree for big estates, shads leaves year around with major drop in late spring and during dry season. It’s better to have deposit area around trunk because of tree littering habit; it’s also known that roots have inhibitors to suppress vegetation grows particularly to its’ own species.
In Bay Area Silver Oak blooms in May- June. Spider-like orange flowers are set in almost 7 in long dense clusters. The foliage very ornamental as well – big 12 in long deep green on top and silvery underneath fern-like leaves. Trunk is deeply grooved, dark gray.

Grevillea robusta loves heat and full sun, can take some shade. Best grows with even water distribution during the year ~ 50 – 100 in and has tendency to die back at maturity (age 15-20 years) from prolonged drought stress (more than 4 month) even though seems pretty drought tolerant at younger age. Adapted to wide variety of soil types, prefers slightly acidic to neutral – can tolerate clay with good drainage. Roots runs shallow without drought stress.
This quick to grow, rot resistant timber ones was widely used by Australian cabinetmakers as it works easily and has lace-like grain but may cause contact dermatitis. Silky Oak was introduced widely in temperate regions around the world; it escaped cultivation and became weedy in Hawaii, New Zealand, some parts of India, China and South Africa. Tree considered an important source of nectar for apiaries, timber, firewood and leaf mulch.
Caution: The flowers and fruits contain toxic hydrogen cyanide; wood may cause contact dermatitis.

Plant profile summary:

Name Grevillea robusta (Silk Oak)
Zone/ Sunset Zone Zones 9-12, Sunset 8,9, 12-24
Type: Tree
Size/shape: Up to 60 ft x 30 ft wide (some specimen can be almost twice as big), pyramidal at young age with more pronounced big limbs and somewhat widened crown at maturity
Life Span: Medium lived – matured around 20 years may live up to 50 years
Foliage/ Flower/ Fruits Type/ Color Evergreen, big 12 in long deep green on top and silvery underneath fern-like leaves. Blooms in May- June. Spider-like orange flowers are set in 7 in long dense clusters. Great source of nectar. Fruit it hard, dry pod-like follicle 0.8 in diameter contains one or two winged seeds.
Sun/ wind Exposure: Full sun
Water requirements: Drought tolerant at young age, may die back with prolong drought stress at mature age.
Soil requirements: Wide range of soil: slightly alkaline–neutral-slightly acidic, clay, serpentine as long as it has good drainage
Use: In Bay area mainly used as Ornamental and shade tree for big estates, along the freeways and roads as well as rootstock for other Grevilleas.
Attractions – special features: Architectural branches and trunk, tropical look, spectacular blooming show
Pests / Diseases: In Bay Area hardly any
Trimming Conforms to trimming and pollarding, may be trimmed if needed as wood is brittle and may not sustain strong winds.
Caution: The flowers and fruits contain toxic hydrogen cyanide; wood may cause contact dermatitis.




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