QBARS - v23n2 Growing Malesian Rhododendrons in Australia

Growing Malesian Rhododendrons In Australia
A. W. Headlam, Bentleigh, Australia

Considerable progress has been made over the last seven or height years in growing Malesian Rhododendrons in Australia.

One of the first introductions was R. christianae , which was grown from seed collected at an altitude of some 2000 feet in the Daga country of South East New Guinea by a good friend of the Australian Rhododendron Society, the Rev. N. G. G. Cruttwell. The seed was germinated on pure peat, and when the seedlings reached three or four inches high, they were distributed to members. In about three years the first flowers appeared, each truss having six or seven florets with deep yellow tubes, shading to a bright orange/yellow at the lobes.  The tubes are usually about ½" in diameter, 1½" long, and the corollas measure up to 1½" across the lobes.

R. christianae , which was named after Rev. Cruttwell's mother, has undoubtedly been the most prolific of the New Guinea species, for it is rarely without a flower or two. The main flowering season in Australia is from late spring to mid-summer, when the plant is covered with flowers.

Another species which has proved easy to grow and has produced many fine flowers of a deep yellow color is R. laetum . The flowers have a wax-like texture, and are produced in trusses of seven or height and sometimes up to eleven florets - the color deepens with age, and occasionally some flowers become suffused with rose or lavender tinges. Seed of this species was collected at about six thousand feet in the Arfak Mountains by Dr. Sleumer, where he also collected seed of R. arfakianum , but the latter species has not been so prolific, and only a few plants have flowered, the trusses bearing up to seven tubular flowers, usually deep pink in color.

R. aurigeranum is another species which has flowered quite prolifically, producing trusses with up to twelve flowers per inflorescence, the color of which has varied from pale yellow to a fairly deep orange. This species grows in considerable numbers on grassy hillsides and amongst rocks in the Bulolo Wau district of New Guinea.

R. inconspicuum is one of the New Guinea species which has proved somewhat disappointing in Australia  - its growth has been slow and the small pink flowers, the corollas of which are only half an inch in length, have been very sparse, quite the reverse to Rev. Cruttwell's description of it growing in the Arfak Mountains and on Goodenough Island, where it is most prolific, and en masse, makes a brilliant display of color.

I had two plants of this species, one of which died, and the other was moved to a position in the shade house where it is making vigorous and healthy new growth. Now that it appears to have become acclimatized, it is hoped that it will flower more prolifically.

A very striking species is R. zoelleri , the trusses, usually carrying five or six large florets, have been orange, sometimes suffused with red, and a lime green throat. However, the seedlings have been somewhat lacking in vigor and difficult to grow, consequently very few flowers have been seen. Seed together with that of R. phaeopeplum was collected by Dr. Sleumer in the Arfak Mountains. R. phaeopeplum however, proved to be much more vigorous in growth, and produced trusses with six or height florets, some pure white and some with pink tinges of varying intensities on the tubes, and having, particularly after sunset, a heavy carnation-like perfume.

R. phaeopeplum is considered to be a minor edition of R. konori , one of the largest and finest of the New Guinea rhododendrons. A number of plants of R. konori have been raised, some with quite vigorous growth, but only very recently have the long awaited flowers appeared, from one of a number of plants growing in a glass house. The four white tubular flowers were about four inches in length, and had a strong perfume. This is very probably the first of this species to be flowered anywhere outside of New Guinea.

I asked Rev. Cruttwell if he would photograph R. konori for me when a favorable opportunity occurred, and his reply enclosing two very interesting transparencies is just to hand:

" Well, here it is. It flowered here on the Mission Station and I took a series of shots. It produced a beautiful spray of six great white flowers. The close up shows the detail and the one with the little girl, who would not smile, gives the scale - it is approximately six inches in diameter. The scent is magnificent, and fills the air for yards around. I think the nearest resemblance is carnations, in distinct variation from my latest unidentified species where it is unmistakably hyacinth."

R. gracilentum , one of the smaller species which grows both terrestrially and as an epiphyte in the Nothofagus forest in the Edie Creek area, produces numerous tubular dark pink flowers which hang singly and attractively against a background of small olive green leaves. Undoubtedly, the best of this species is one growing in a piece of tree fern log - it is rarely without a flower or two, and as summer approaches it is seen at its best, covered with a mass of flowers.

Seed of R. macgregoriae , which is distributed fairly widely over New Guinea. and grows generally terrestrially, making a brilliant display of color from pale yellow to deep orange yellow, was collected at 1000 feet on the Vogelkop Peninsular in 1961 by Dr. Sleumer.

Plants were distributed to Members by the Australian Rhododendron Society and the first flowers were seen in 1965, with up to 15 orange/yellow florets forming a rounded truss of some five inches in diameter.

R. javanicum , a species indigenous to Java, Sumatra and Bali, flowers quite freely, producing from height to eleven florets, deep yellow on opening and usually increasing in depth with age until a deep orange color is reached, sometimes a reddish tinge appearing inside the lobes.

Other Malesian species flowered have been R. jasminiflorum , R. leptanthum , of which only one plant has flowered with four small tubular pink florets, and R. retusum , several plants having flowered with up to seven tubular bright red flowers.

Two Malesian hybrids produced by the well known English nursery of Veitch some 100 years ago, 'Pink Delight' and 'Triumphans' are also grown here - an attractive plant of 'Pink Delight' covered with bright pink flowers has been exhibited in a Trade display at the Australian Rhododendron Society's Annual Show at Olinda for the last two years.

Some hybridizing between the New Guinea rhododendrons and the only rhododendron indigenous to Australia, R. lochiae , found growing both terrestrially and as an epiphyte in the mountainous rain forests of North Queensland, has been carried out, and plants of R. macgregoriae x lochiae and R. lochiae x christianae were raised and distributed to members some years ago.

Quite a number of these have flowered - the lochiae x christianae hybrid has produced loose trusses of up to eleven flowers, in shape fairly closely resembling R. lochiae , but with some variations in color, from red to orange/ red tonings.

The R. macgregoriae x lochiae cross has proved easy to grow, is quite vigorous and has produced trusses of up to 25 flowers of an orange to orange red color.

The tubes are ¼" in diameter by ½" long and the five lobed flowers are usually 1¼" across. Pedicels are red and about one inch in length - trusses with around 15 florets are somewhat flat on top; however, when there are in the vicinity of 20 to 25 flowers, the truss is round and generally from 4½ to 5 inches in diameter. The new growth is often bronze in color, and on reaching maturity turns to a deep glossy green, making an attractive background for the profusion of orange red flowers.

Generally, most of the Malesian species have been grown under glass, but not having a glass house, nor the room in an already somewhat overcrowded garden to build one, I decided to try and grow them in a semi-sheltered position.

In a corner made by two walls of our house, over which there is a 12' x 10' roof of corrugated plastic to give the back entrance some protection from the elements, a bed 6' x 4' was formed by a wall two bricks high. My wife had planned this bed for Indica Azaleas, but somehow the Malesians took possession and they have never looked back since.

The bed is so located that it receives morning sun until about noon each day, and is protected from the worst of the prevailing winds by the two walls of the house. Having read that many New Guinea rhododendrons in their native habitat grow fibrous roots in the moss and leaf mould on the surface, and have tap roots which penetrate into the clay below. I endeavored, as far as possible, to create similar conditions. The soil was removed for about 12/15 inches to a thin layer of gravel and stone, under which there is a heavy band of clay, and the bed then filled with a mixture of peat moss and fern fiber, 40%, sandy loam 25% and the balance red pine buzzer chips, all very thoroughly mixed.

The California redwood chips which increase acidity and maintain an open and friable texture, thus providing a free root run, do not rot away like other timber, so there is no problem of Nitrogen deficiency.

Rhododendrons planted in this bed are R. konori , javanicum , commonae , laetum and the hybrids macgregoriae x lochiae and lochiae x christianae - they have all grown extremely well and all have flowered with the exception of R. konori and commonae .

They are sited where they receive morning sun until about midday and show no signs of distress, even when the temperature often exceeds 100 deg. F., in midsummer. On the other end of the scale, our winters are relatively mild, and temperatures rarely fall below 32 deg. F., so no problems are encountered in this direction. Malesian rhododendrons growing in a concrete window box and other containers in this semi-sheltered area are R. lochiae , gracilentum , jasminiflorum x christianae , macgregoriae x laetum and the previously mentioned hybrid 'Triumphans'.

Seed of Malesian rhododendrons loses its viability quite rapidly, and six weeks seems to be the limit which can elapse between gathering and planting if successful germination is to be achieved.

Fertilizer is applied by means of a foliar spray, usually at monthly intervals, and in early spring and late summer a light dressing of pulverized cow manure is applied and thoroughly watered in.

It is detrimental to allow them to become too wet in winter months, but in summer when the evaporation rate is high, they are watered often twice daily, and seem to particularly appreciate overhead spraying of the foliage for this attention the credit must be given to my wife who never misses keeping the water up to them.

Looking at our bed of Malesian rhododendrons this summer, with R. christianae covered in flowers, the lochiae x christianae hybrid showing seven or height trusses of bright red flowers, the macgregoriae x lochiae hybrid with no less than 26 trusses of orange red flowers ranging from 16 to 25 flowers per inflorescence, and looking particularly attractive amongst the dark green glossy leaves, whilst a number of buds were rapidly filling on R. javanicum and laetum , with R. lochiae in full flower in a nearby container, I feel that there is little doubt that the Malesians will come into their own in a world of rapidly shrinking gardens, where in many large cities with blocks of flats and housing units with little or no gardens are the order of the day.

What other six rhododendrons, even dwarf varieties, could grow so attractively and provide flowers in such an abundance over such a long season in a bed measuring only six feet by four feet?