Common Name: Silky Oak

General Information

Grevillea robusta is a deciduous tree with a dense, conical crown; it can grow 12 - 25 metres tall with exceptional specimens up to 40 metres[]. The bole, which can be 80 - 120cm in diameter, is straight, unbuttressed, and can be free of branches for up to 15 metres[].
The tree is often cultivated in the tropics for timber and as a windbreak[]. It is a very ornamental plant, valued especially for its attractive fern-like foliage and brilliant orange floral display; it is often grown in gardens and as a street tree[, ]. The tree flowers freely in subtropical areas, but only poorly in the lowland tropics[].

Known Hazards

This species has occasionally caused contact dermatitis following contact with the foliage or sawdust[]. This is due to due to tridecylresorcinol, a chemical compound related to the allergen toxicodendron[].
The flower buds, fruit and seeds are cyanogenic[].

Botanical References

, ,

Range

Australia - New South Wales, Queensland

Habitat

Riverine rain forests, usually by water, on soils of fairly high fertility[]. Also found in vine forests, which cover extensive areas including steep upper-valley slopes[].

Properties

Edibility Rating
Other Uses Rating
Habit	Evergreen Tree
Height	20.00 m
Growth Rate	Fast
Pollinators	Birds, Fruit bats, Bees
Cultivation Status	Cultivated, Ornamental, Wild

Cultivation Details

Succeeds in warm temperate to tropical regions[]. In tropical areas it can grow at elevations from 130 - 2,300 metres, whilst in the temperate zone it is found from sea level to 1,000 metres[]. The plant is found in areas where the mean annual rainfall is in the range 700 - 1,700mm, with a dry season of 0 - 6 months[]. The mean maximum temperature of the hottest month is 25 - 31°c, the mean minimum temperature of the coldest month is 2 - 12°c, and the mean annual temperature is 14 - 23°c[].
An easy and fast-growing tree requiring a well-drained slightly acid soil and a sunny position[]. It prefers a rich moist soil[], but it also succeeds in dry soils. Dislikes limey soils and heavy clays[, , ]. Established plants are drought resistant[, ]. Dislikes strong winds[]. Succeeds in soils with a pH in the range 4.5 - 8[]. On acid soils, symptoms of boron deficiency and manganese toxicity have been observed[].
The tree first flowers when about 6 years old. In its natural range, flowering occurs over a few weeks in October-November, but when planted in equatorial latitudes, flowering is sporadic throughout the year or absent[].
When climate and soil are suitable and weed competition is not severe, annual height and diameter increments of at least 2 metres and 2cm, respectively, are usually achieved for the first few years in row planting on farms. Annual height increments of 3 metres have been observed at the most favourable sites[].
Grevillea robusta regrows well after complete defoliation following pruning and pollarding, which can be carried out repeatedly to yield wood and to regulate shading and competition with adjacent crops[].
The tree is characterized by root suckering, hence it is a good candidate for management under coppice rotation; it responds well to pollarding, lopping and pruning[].
The leaves and twigs are apparently rich in aluminium[].
Hybridizes freely with other members of this genus[].
The flowers are very attractive to bees[].
Plants in this genus are notably resistant to honey fungus[].

Edible Uses

The flowers are one of the richest sources of nectar[]. This can be sucked directly from the flowers, shaken into a bowl or washed out in a small quantity of water[]. The nectar falls in showers when the flowers are shaken[].

The leaves contain rutin, though quantities are not specified[]

Medicinal

None known

Agroforestry Uses:

This tree is one of the most important reforestation trees in Nepal[]. It is a pioneering colonizer of disturbed sites[].
An excellent agroforestry species as it interferes little with crops. Best growth is obtained when it is planted in rows or intermixed with crops[]. It is regarded as more compatible with crops on small farms than most other tree species[].
The leaves are used as a mulch[].
The silky oak provides abundant quantities of leaf mulch, which may accumulate to a depth of 30 - 40 cm. This thick layer protects the soil and maintains soil temperature[].
It is used to provide high shade in tea and coffee plantations[, ].

Other Uses

The plant yields small quantities of a gum resin[]. By virtue of their solubility, viscosity and relatively high resistance to hydrolysis, the gums may have some industrial applications[]

Intense yellow and green dyes are obtained from the leaves[].

This species is more resistant than other members of the genus to root-rotting fungus, it is sometimes used as a rootstock for the more susceptible species[].

The heart-wood is distinctly pink or light red when freshly cut, turning pale brown or red-brown on exposure; the band of white or straw-coloured sapwood is about 40mm wide[]. The texture is medium to coarse; the grain may be straight or wavy; growth rings are not distinct; large rays give the wood an attractive figure on both the quarter-cut and back-cut surfaces; the vessels contain some red deposits. The wood is strong, light in weight, durable but porous. The wood saws easily, apart from gumming up the saw-blades; stock moulds easily and cleanly, but 10° cutting angle required to obtain good finish on quarter-cut faces; mortising and chiselling properties usually good; material needs scraping to ensure a good polish; it stains readily; takes nails easily but splitting may occur - nail
holding power medium to low. It is easily split. The wood is used for panelling, joinery, cabinet making etc[, , , , ]. It is suitable for pulping[].
A popular plant for firewood and charcoal. It is also used to fuel locomotives and river steamers, power boilers etc. The calorific value of sapwood is about 4800 kcal/kg, while that of heartwood is 4950 kcal/kg[, ].

Propagation

Seed - sow late winter in a warm greenhouse. Germination is usually good[]. When they are large enough to handle, prick the seedlings out into individual pots and grow them on in the greenhouse for at least their first winter. Plant them out into their permanent positions in late spring or early summer, after the last expected frosts.
Cuttings of half-ripe wood, 5 - 8cm with a heel, early summer/July in a frame[].