introductions of rhododendrons were the result of plant
hunting expeditions funded by the new wealth of the industrial
revolution, competing fiercely with each other to fill
their conservatories with exotic horticultural curiosities.
This emerging wealthy class could afford estates of the
scale necessary to accommodate species impractical for
the smaller suburban garden, so size was no limit. As
a result, many of the hybrids bred from these earlier
introductions tended also to be impractically large.
of a number of forms of Rhododendron arboreum
shoots of the giant Rhododendron sinogrande
of a number of forms of Rhododendron sinogrande
the turn of the twentieth century and the rise of the
middle classes, home gardening became more popular, and
the thrust turned to the breeding of compact plants with
showy, colourful flowers. This trend was spurred on by
the discovery of low-growing species such as the strong
red prostrate R. forrestii (George Forrest, Tibet,
1905) or R. degronianum ssp. yakushimanum.
Japanese collector Nakai, Yakushima Island, 1921) and
interest in the larger species started to wane. The frost
tenderness of many early introductions, used to growing
as sheltered understorey plants, also tended to restrict
their success in the cooler northern hemisphere climates.
the so-called 'tree' rhododendrons are forest dwellers
growing at altitudes of between 2,500 and 3,000 m or more.
Some species grow in dense, tangled forests where they
are virtually the sole species. Others dominate the understorey
beneath a canopy of taller evergreen or deciduous trees,
through which frosts rarely penetrate. These may be birches,
magnolias, maples, oaks or chestnuts, while at higher
altitudes the conifers takes over - spruces, silver firs
size these plants attain in the wild is, to some extent,
the result of the abundant moisture available to them,
particularly the monsoonal summer rains found in most
of the growing areas. As spring growth commences over
February and March, they are amply watered by melting
snows. Thus, they live in an environment with a virtually
continuous supply of abundant moisture. For this reason,
every effort should be made in cultivation to protect
them from the drying effects of hot sun or wind as well
as frost, a woodland setting being ideal.
will take quite a few years to reach flowering, at least
twenty or more, while at least fifty years is needed for
a tree rhododendron to reach its optimum form. Many are
worth growing for their splendid foliage alone, particularly
the charming 'candlesticks' formed by the erect young
leaf shoots in spring.
species tend to be elepidotes, without the covering of
fine scales over the foliage which assist the plant in
transpiration. The Himalayan species R. nuttallii is
an exception, a lepidote in the Maddenia subsection which
reaches about 10 m in ideal conditions. It makes a good
choice for Australian gardens, being quite heat and sun-tolerant,
although it is inclined to wilt alarmingly when conditions
become dangerously dry.
Rhododendron arboreum ssp. zeylanicum
the best known of the tree rhododendrons is the obviously
named R. arboreum, which is distributed widely
across the Himalayas, China, Thailand, India, Myanmar
and even as far south as the highlands of Sri Lanka. It
has been recorded as reaching heights of up to 20 m, although
it is more usually half that height or less, with glossy,
deep green leaves bearing a white or fawn indumentum underneath.
best known form of R. arboreum has tight, globular
trusses of around twenty blood red flowers, borne from
July to October, although other forms are various shades
of white, pink or red. The red forms tend to be more tender.
A number of local variations which were formerly classified
as distinct species are now regarded as subspecies of
R. arboreum, including R. delavayi
(Abbé Delavay, West Yunnan, 1883) and R.
zeylanicum reaches about 10 m in the wild, with distinctive
spiral bark markings, and dark green bullate leaves with
a thick brown indumentum. Its flowers are normally blood
red, although there are pink forms, borne in October and
November. It is native to Sri Lanka and Manipur in Assam.
from the Arborea subsection, R. lanigerum forms
a shrub or small tree to about 6 in, very similar in form
to the later-flowering R. niveum. It bears large,
rounded trusses of purplish, bell-shaped flowers between
August and October. Its delightful young growth is covered
with a creamy-white tomentum. It was first collected by
Kingdon-Ward in 1928 in the Delei Valley, Assam.
grande was discovered by Wight in Bhutan around 1847
and is found growing at between 1,700 and 3,600 m in eastern
Nepal, Sikkim, Bhutan, southern Xizang and Arunachal Pradesh,
where it has been recorded at up to 15 m. Its leaves,
which follow distinctive pink bud-scales on new shoots,
have a woolly, silvery or fawn undumentum, and can reach
as long as 45 cm. Flower trusses, which bloom between
August and October, consist of up to 25 cream, pale yellow,
pink or deep rose flowers, spotted and with a purple blotch.
The relatively early flowering and subsequent early leaf
growth of this species demands a well-sheltered site as
the foliage is very susceptible to wind and frost damage.
While R. grande gives its name to the Grandia
subsection, other close relatives are notable as the among
the largest of rhododendrons.
at 2,100 to 4,300 m in East Arunachal Pradesh, Yunnan,
upper Myanmar and southeast Xizang, and was discovered
in 1912 by George Forrest in the Salwin-Kiu Chiang Divide,
in southeastern Xizang. It forms a large shrub or medium-sized
tree reaching about 12 m with certainly the largest, and
possibly the most handsome of all rhododendron foliage.
creamy bell-shaped flowers, borne in huge trusses around
October, seem almost an afterthought to the huge, dark,
leathery leaves which diminish in size as flowering age
is reached. A more northerly form has soft yellow
flowers. Like the other large-leaved species, R. sinogrande
demands plenty of shelter but will tolerate a reasonably
sunny position, although the largest foliage is borne
on plants that are well shaded and growing in constantly
classified as a form of R. sinogrande, the deep
pink or rosy purple flowers of R. montroseanum are
regarded as the finest of pinks in larger species. It
reaches up to 15 in m the wild, with foliage up to 45
cm long, similar in form to both R. sinogrande and
R. grande. A Kingdon-Ward discovery, it is found
in the Tsangpo Gorge in southeastern Xizang at altitudes
of 2,400 to 2,700 m, where it can constitute up to 50
per cent of the temperate rainforest in which it grows.
in the Grandia subsection, R. giganteum was discovered
by George Forrest in 1919 in southwestern Yunnan. Perhaps
the largest of all rhododendrons, it has been recorded
at over 30 m in height, with a massive girth of trunk
of almost 2.5 m at 1.5 m from ground level.
forms of R. barbatum grow into graceful small trees.
As its name implies, twigs and leaf stalks are covered
with stiff, bristly hairs. It has lovely smooth reddish
bark, and, like others with smooth bark, tends to resent
too much pruning. Its compact trusses of rich red flowers
are borne around September.
from the Grandia subsection, grows at 2,400 to 2,700 metres in
in the Naga Hills,Assam, and Manipur in northern India,
amongst birches or as compact forests on its own.
was discovered by Sir George Watt in 1882. It reaches
up to 15 m in the wild, and has leathery, dark green leaves
reaching 30 cm, with a whitish woolly indumentum underneath.
New shoots form a spectacular display of silvery 'candles'
covered in distinctive bright red bud scales. Its huge
trusses of up to twenty cream to bright or lemon yellow
flowers are profusely borne in September to October. In
comparison to other large-leaved species, it is relatively
tolerant of wind, frost and drought, and thus makes an
ideal garden plant.
magnificum, from around
the Myanmar-Xlzang frontier at 1,500 to 2,400 metres, is very
similar in form to R. prostitum, although it is
recorded as being hardier and more floriferous. It was
discovered by Kingdon-Ward in 1931 in the AdungValley,
Myanmar, and can reach as much as 18 m in the wild, although
it is always far smaller, typically to 6 m, in cultivation.
It bears trusses of up to thirty floppy deep rose to crimson
or reddish purple florets from August to October.
falconeri can be a spreading tree with several trunks
reaching about 16 m, although it rarely reaches half that
height. It has reddish-brown bark and its leaves which
reach 30 cm or more in length have a rich brown indumentum.
Young shoots have a temporary covering, of pale brown
fur and its creamy yellow bell-shaped flowers flowers
are borne in large rounded trusses in October and November.
R. falconeri was first described by Sir Joseph
Hooker in Sikkim in 1849, and is widely distributed across
Nepal, Sikkim, Bhutan, western Arunachal Pradesh and Assam.
in the Falconera subsection, R. fictolacteum is
a highly variable species, but particularly impressive
is the large-leaved form from western China. It has bell-shaped
white, cream or pink flowers with a purple blotch, borne
in October-November. It was discovered by Abb& Delavay
in 1886, growing in western Yunnan.
calophytum, from the Fortunea subsection, is distinguished
by its distinctive and elegant long, narrow leaves. It
reaches 15 m in its native western Szechuan. In September
to October it carries large trusses of white or pink flowers
marked by a reddish blotch.
are by no means all of the rhododendrons which can qualify
as tree species, but a representative selection. Fear
of excessive height should not deter the growing of these
potentially large plants in domestic gardens. In cultivation,
they are very unlikely to attain proportions achieved
in their natural environment, the larger broad-leaved
species being understorey plants whose inclination is
to grow tall and leggy to reach the scant light available.
specialist rhododendron suppliers in Australia
Grove Nursery, Cattai
Ridge Road, Glenorie, NSW 2157. (02) 9652 1200.
Rare Plants, 686 Mount Macedon Road, Mount Macedon,
Vic. 3441. (03) 5426 3075.
National Rhododendron Gardens, The Georgian Road,
Olinda, Vic. 3788. (03) 9751 1980.
Valley Nursery, Woori-Yallock Road RSD, Cockatoo,
Vic. 3781. (03) 5968 8676.
article was originally written for publication
in the International Dendrology Society's Australian
Branch Newsletter, September 1997 and later
in the 1998 issue of The Rhododendron,
Official Journal of the Australian Rhododendron
to and use of the material provided on these
pages is acceptable, but please respect my rights
when considering commercial use in return for
my trust in offering the material for public
25 January 2006
Text and photographs © 1997-2006 Richard
to Alistair Watt, Lavers Hill, Victoria, Australia,
whose plants are illustrated on this page