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

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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	25.00 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 - they have no dormancy but germination is delayed and uneven. Soaking the seed in cold water for 24 hours prior to sowing may improve germination[]. Seeds can be sown in well-drained, shady seedbeds or individual containers, using with equal proportions of sandy loam and sand. Germination is usually good, occurring after 2 - 4 weeks[, ]. When the seedlings are 7 days old, they are pricked out in polytubes. Shade is required for the first 2 - 3 weeks after transplanting[]. In about 6 - 8 months, when the plants are 20 - 30cm tall, they can be planted out into their permanent positions[].
Cuttings of half-ripe wood, 5 - 8cm with a heel[].

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