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GENERAL
Origin
:
Mediterranean,
sub-tropical,
tropical
Vigour
:
fast growing
Humidity
:
semi-arid, semi-
humid
Propagation :
sowing and
pricking out,
cuttings
Maintenance :
moderate
CONDITIONS
Urban climate :
vulnerable
Dessication :
vulnerable
Stagnant water :
vulnerable
Irrigation
:
medium
Salinity/ppm :
moderate (2500
ppm)
Hardiness
:
-6°C
SHAPE
Type
:
tree
Height
:
13 m-50 m
Spread
:
7 m-20 m
Foliage
:
evergreen
FLOWER
Colour
:
deep yellow,
deep orange
Size
:
7 cm - 10 cm
Period
:
March - May
FRUIT
Type of fruit :
drupe (leathery/
fibrous)
Fruit size
:
3 cm
The Silk Oak is a strong, enduring tree that reaches a maximum height of 50 metres. However,
such growth can be expected only in its native country, Australia. Although it grows quite fast,
it will usually not exceed 13 metres, especially in Arriyadh. The tree has a conical, upright form.
Fern-like, lacy leaves are shiny green on top and silvery below, while the showy orange flowers are
borne in large clusters on the branches, usually when the tree is in a semi-deciduous state after
the winter. Silk Oaks are considered evergreen, but foliage may be shed owing to cold, or when
the new leaves appear. It will tolerate a wide variety of soils, but these should be well drained.
Waterlogging and alkaline desert soils limit the speed of growth and cause iron chlorosis. The
wood is brittle and wind exposure may cause branches to die back or break off. Propagation is by
seed or cuttings. G. robusta is a background tree for use in parks and in public squares. A mature
tree makes a picturesque silhouette against the sky. Heavy pruning is possible, but may spoil the
columnar or pyramidal shape. It has toxic qualities. Grevilleas may sometimes cause painful skin
irritation. Regular irrigation is necessary at first, but a mature tree is generally drought-resistant
and requires a deep soaking every month or so. Heavy leaf litter in spring necessitates a lot of
tidying up from lawns and paving, although it can be left as mulch on the soil. This tree is rarely
seen in Arriyadh, although it has potential for planting in protected situations.
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Grevillea robusta,
Proteaceae
Grevillea,
Silk Oak