Malesian Rhododendrons in Australia
Reprinted from the Proceedings and Papers of the Pacific Rhododendron Conference
Malesian rhododendrons are outstandingly beautiful. They have the biggest flowers in the genus; some are fragrantly perfumed and they are renowned for their pure and intense colors. These colors do not fade but deepen as the corolla ages. If their few cultural requirements are met the Malesians are exceptionally easy to grow and are most rewarding with their flowers. Frequently, every branch is covered with flowers making the entire plant into an exquisitely beautiful bouquet that will last indoors in perfect condition for one month.
There are some 850 species in the genus rhododendron and of these some 300, or more than one third, are Malesian species. The Malesians are further enriched by local forms and variants. An example of this is the spectacularly beautiful R. zoelleri of which the Australian Rhododendron Society now has 18 collections each of which has slightly different characteristics. The most interesting aspects of this collection of R. zoelleri are that the plants vary in cultivation from the weakest to the strongest growers. Dr. Hermann Sleumer, in his monumental work, has classified the bulk of the Malesians in the lepidote section Vireya which, outside Malesia, has two species in Indo-China, R. kawakamii in Taiwan, R. vaccinioides in China and the Himalayas and R. lochiae in Australia. Some 160 of the Malesian species are endemic to New Guinea.
The first New Guinea rhododendron received by the Australian Rhododendron Society was R. christianae which was raised from fresh seed sent by our very good friend Reverend Canon Norman Cruttwell on 5th, September, 1959. Canon Cruttwell had collected this seed between 2,000 and 5,000 feet, especially on cliffs and steep places, in the Daga area, Papua, New Guinea. The seed was germinated by the foundation President of the Australian Rhododendron Society, Alf Bramley, and the young plants, three to four inches high, were distributed to members of the Society, both in Australia and overseas, in May, 1961. This was the first general distribution of New Guinea rhododendrons anywhere in the world.
The distribution of our first New Guinea rhododendron created tremendous interest, and, resulting from this, we wrote to Dr. Hermann Sleumer, at Boskoop, not knowing that he was already in the concluding stages of a seven month expedition to New Guinea. Fortunately, the letter was forwarded to New Guinea and from his very last collection in the field in February, 1962, Dr. Sleumer sent seed of R. arfakianum, asperum, erosipetalum, konori, laetum, inconspicuum, macgregoriae, phaeopeplum and zoelleri. Good germination of each of these was obtained and, subsequently, plants were distributed to members and also, by special request, to Strybing Arboretum and to Kew.
In April, 1965, the energetic and amiable Michael Black flew to New Guinea to collect rhododendron plants and seeds in order quote, "to assess their undoubted horticultural value". He was greatly impressed by their sheer beauty and the clarity of the colors. In three months he collected a large amount of plant material which he generously shared with this Society. He has since been back to New Guinea and, presently, he is on another plant hunting expedition but has been delayed awaiting visas and this has prevented his attendance at this conference. In 1968, he took time off from his second expedition to New Guinea to come to Melbourne to deliver the yon Muller Memorial Lecture. It is not generally known that during his visit there was hardly a patch on his body not tender and sore from pock marks of the leeches encountered a few days earlier in the dripping jungles of New Guinea.
For ready access to the magnificent beauty of the Malesian Rhododendrons the Australian Rhododendron Society is greatly indebted to Dr. Michael Black, Dr. Hermann Sleumer and Reverend Canon Norman Cruttwell and the many others who have so generously given of their introductions.
R. christianae first flowered in Australia in October, 1963 (exactly four years from seed) and, almost simultaneously, both Alf Bramley and Tom Lelliott were successful in hybridizing it with the Australian R. lochiae. This proved to be the first man-made hybrid to be raised from a New Guinea species! Early in 1966, two-year-old plants of this cross together with plants of the hybrid R. macgregoriae X R. lochiae were distributed to members of the Australian Rhododendron Society both in Australia and overseas. These hybrid seedlings immediately proved to be far more vigorous and easier to grow than the species. First flowers were obtained on the R. christianae hybrids at just under three years from seed and this set the pattern for the flowering of all Malesian hybrids except those grown with extensive supplementary light where blooms were obtained at 17 months from seed.
The Malesians, both hybrids and species, hybridize quite readily with each other and, needless to gay, numerous hybrids have been made. In the initial stages R. christianae was crossed with every available species and with the Veitch Hybrids. The best of the R. christianae hybrids, to date, is probably the cross with the yellow form of R. macgregoriae. This hybrid proved very easy to grow and most of the seedlings flowered at three years from seed. The most floriferous of the three year-old plants had 21 trusses each of 14 florets and provided a most attractive show of "sunset orange" flowers for one month from its six inch pot. Surely, the most optimistic rhododendron hybridist could not expect more in so short a time except from the Malesians.
As a general rule, the larger the leaves the easier it is to cultivate the Malesian species. It is considered that the reason for this is that the species with larger leaves come from lower elevations which experience heat and both wet and dry periods. Because of this they appear to have an inbuilt tolerance to both heat and dryness. On the other hand the small-leafed species come from high altitude and alpine areas where rainfall and mists are so heavy and frequent that the plants are always wet and cold. Experience has shown that small-leafed species cannot tolerate any dryness and that they do not like excessive periods of heat. For these reasons the small-leafed species are, as a general rule, quite exacting in their cultural requirements. In their natural habitat frost is not experienced generally below 8,000 feet and, therefore, all species from lower altitudes do need protection from frosts. However, they do not need warm house conditions. Experience has shown that they thrive best outdoors and that they are more compact and floriferous with plenty of sunshine.
The seed of the Malesian is quite distinct in that they have appendages at both ends which resemble tails but act like wings. When the seed is ripe the outer layer or skin of the capsule begins to peel. When this happens in warm weather you have a margin of two or three days to collect the capsule before the ovary opens and hundreds of seeds are wafted away on the breeze. Our experience has shown that viability of the Malesians is of the order of six weeks and that generally after this period it is a waste of time to plant the seed. Fresh seed germinates and grows quite well on pure peat which should be quite damp but with all surplus water squeezed out. The young seedlings grow comparatively slowly for the first 12 months. However, growth can be accelerated by taking small tip cuttings as per John Patrick's method and also by the combination of supplementary lighting and foliar feeding.
Malesian rhododendrons root quite readily from cuttings with or without the use of hormones. Under good conditions cutting material can be taken at any time of the year; the only real difficulty is access to cuttings of the choice sorts. The size of the cutting is not vital and can vary from four inches down to half an inch. Best results are obtained with cuttings two to three inches long. If the wood is firm to hard it is best struck in a mixture of peat and sand. If the wood is soft it is best struck in sphagnum moss which inhibits rot and fungi. The cuttings will strike quite readily without heat during the warmer months but, needless to say, optimum results are obtained with heat. The struck cuttings will respond to and thrive with supplementary lighting which, for convenience can be fluorescent lamps. In the initial stages I grow the struck cuttings for 18 hours a day and they invariably flower when they are 14 months old.
In grafting the Malesians experience in Australia has been contrary to published overseas reports that R. konori can be successfully grafted onto R. ponticum. It is our experience that grafts of R. konori and other Malesian lepidotes are not truly compatible with R. ponticum. In most cases the grafts appeared to unite quite well with good callusing on both the scion and the under-stock but, sometimes several months later, the union between the two invariably broke apart under stress.
At this stage you may well ask why it is necessary to graft the Malesians when they strike so readily on their own roots. One of the answers is that in cultivation a few choice sorts are hard to please on their own roots. One of these is the strikingly beautiful R. zoelleri collected by Dr. Sleumer on his very last trip by helicopter to the Arfak Mountains, West Irian, on 7th February, 1962. This beautiful "prima Donna" is quite fastidious, slow growing and temperamental on its own roots but performs outstandingly well when grafted. Undoubtedly the best stocks to use are Malesian hybrids which are generally quite vigorous. These stocks can be grafted easily and successfully, at any time from the second year to ten or more years of age. On no account, therefore, should vigorous rejects from the hybridizing program be thrown into the incinerator. If used as grafting stocks they will provide accelerated growth of the more desirable hybrids and species.
Recent experience has shown that the Maddenii hybrid, R. 'Fragrantissimum', has good potential as a grafting stock for the Malesian lepidotes. As you all know, R. 'Fragrantissimum' (edgeworthii x formosum) is a vigorous hybrid which received the First Class Certificate more than 100 years ago. It strikes most readily and quickly produces an above-average root system. The grafts of the Malesian lepidotes onto R. 'Fragrantissimum' united very quickly and, in the short term, are most promising. If completely successful this could lead the way for further development of the Malesians.
Best Growing Medium
Experience has shown that the Malesian rhododendrons grow best in tree fern logs and several plants in this medium all tend to confirm this point. One of the best of these plants is undoubtedly R. lochiae grown by Lyn Craven, of Black Rock. This plant is a magnificent specimen, three feet in diameter and three feet high. It has been grown in a fern log 14 inches long and 8 inches in diameter for the past eight years. It was placed in the log as a one-year-old cutting grown plant and it is carefully estimated that this plant should continue to thrive in this same fern log for a further 10 years. In other words, an estimated life in the same fern log of between 15 and 20 years.
Fern logs of the dimensions mentioned weigh only a few pounds and are easily moved for display purposes. They provide ideal anchorage for the plant and good aeration for the roots. In addition, plants in fern logs cannot be over watered and the logs do not easily dry out. It is interesting to note that fern logs left in a wood shed for months appeared to be totally dry but when cut in two the centers were moist. If the log is well rotted (and this is preferable but not essential) it also provides some nutrients. Nevertheless, it is necessary to feed the plants in the fern logs during spring and summer and this is easily and readily achieved by fortnightly sprayings of the leaves with a water-soluble fertilizer.
Malesian species and hybrids flower almost continuously throughout the year. The peak of the flowering is in autumn and the lull in the spring when other rhododendrons are at their best.
The following are recommended as the best six species:
- R. superbum - A magnificent rhododendron which combines white and pink colorings, huge lily-like flowers and a rich carnation-like scent to produce a magnificent bloom.
- R. konori - One of the finest of the rhododendrons of New Guinea. The large flowers are pure white with sometimes a pinkish or green tinge and a pink blotch inside the corolla. It has a heavy carnation-like scent.
- R. laetum - The world's best yellow rhododendron on a truly beautiful and well arranged truss. Easy to grow and very showy.
- R. zoelleri - A beautiful and spectacular bi-colored rhododendron. The tube of the flower is generally deep yellow and the lobes suffused with orange, red and sometimes pink.
- R. aurigeranum - Showy, lemon to gold wax-like flowers in a very formal truss.
- R. hellwigii - One of the most magnificent species in New Guinea. The deep blood red rather fleshy flowers literally glow in sunlight and are so outstanding that this species has been named the king of rhododendrons.
Ten years experience in growing Malesians from the wild has shown conclusively that all collections from the wild should be grown and assessed on their own individual characteristics irrespective of whether the particular species has already been tried in cultivation.
In Australia, we have demonstrated our ability to grow the Malesians either from seed or cuttings. Where we have received hundreds of seeds we have reciprocated by sending out, in due course, millions of seeds each with details of the original collection in the wild.
It is considered only a matter of time and experience before the Malesians will be hybridized with the Asian rhododendrons to produce a new race of hybrids with scent and new colors that will flower in the autumn. Nevertheless, the Malesians are so outstandingly beautiful that they are worthy of cultivation in their own right either as species or as hybrids.