There are a great many rhododendrons and to understand them better the huge genus is divided into sections; one of these is section Vireya. Rhododendrons in this section are called Malaysians because many come from the Malay peninsula and adjacent islands. However, others of the section Vireya are found further afield and the name Malesian was coined to embrace the Malay peninsula and the Polynesian islands. However, some members of section Vireya are found beyond even this area and it is clear that geographic appellations can mislead. Furthermore vireyas is shorter.
Vireya rhododendrons are too lovely to lose. Native to mountainous jungles of the Malay-Indonesian archipelago, they have a dark history and have been almost lost to plant lovers since World War I. From the 1800s until recent times, the supply of vireyas, also called Malaysians and Malesians, has been interrupted by war, theft, economic hard times and politics — not to mention the perils of collecting them where climate and terrain are inhospitable. But the dark ages for vireyas may well be over.
Since 1960, botanists and plantsmen have collected, hybridized and grown some 300 species and their hybrids. Despite the disasters that have plagued even these recent propagation efforts, vireyas are now available commercially as plants that home gardeners can enjoy. Throughout the United States, plants are in the hands of competent propagators. As container plants that winter indoors on a sunny windowsill or as landscape plants in areas as mild as Southern California, vireyas are horticultural jewels. They are well-suited to lowered thermostats in today’s homes and the small spaces allocated for gardens in modem subdivisions.
Vireyas bring qualities found nowhere else in the genus Rhododendron. Golden yellows and vibrant oranges lead an array of brilliant colors — pure pinks and fire engine reds to pure whites. Some white-flowered species produce intense fragrances to entice pollinators in the wild, that pervade the home with scents seldom enjoyed beyond a tropical mountainside. Flowers, tubular or open-bell-shaped, are unusually long lasting and plants are generally everblooming. They have lepidote foliage and are drought tolerant. In most cases they do not readily hybridize with hardier Asiatic rhododendrons.
Their beauty alone is worth the plant explorers’ struggles through uncharted, snake-infested jungles that harbor blackwater fever and malaria. The natives of these lands, not always welcoming, have customs unfamiliar to Westerners, such as drying their dead relatives and arranging them around their huts. After a long and perilous history that threatened obscurity to Vireya rhododendrons, these pioneers can feel proud of their victories. They preserve a tradition begun by Victorian horticulturists in England with the discovery of a Vireya called Rhododendron malayanum in 1823 by an official of the East India Company, Dr. William Jack.
Vireyas rose to prominence in England with the work of the James Veitch nursery and its collector, Thomas Lobb. From a handful of species — Rhododendron malayanum, R. jasminiflorum, R. brookeanum, R. javanicum, R. multicolor, R. javanicum var. teysmanii and R. lobbii, Veitch produced over 200 hybrids by 1897. Victorian gentlemen luxuriated in their conservatories and cool greenhouses among the glowing-pink flowers of ‘Princess Royal’, and the snowy blossoms of ‘Princess Alexandra’, an offspring of ‘Princess Royal’ and the white, pink-centered flowers of R. jasminiflorum. But alas, competition from hardier rhododendrons discovered in western China and the Himalaya pushed aside the exquisite vireyas that were thought to be exclusively greenhouse plants.
The hardships of World War I made the keeping of greenhouses and conservatories a luxury even the well-to-do could not afford. Many large gardens were abandoned. The result was the loss of all but ten or twelve of the Victorian hybrids in Great Britain. Remnants of the 19th Century work remembered today are ‘Ne Plus Ultra’, a true Christmas red; ‘Triumphant’, the reverse cross of ‘Ne Plus Ultra’ between ‘Dutchess of Edinburgh’ and Rhododendron javanicum; ‘Princess Alexandra’; ‘Red Prince’; ‘Sybil’, a clear pink that resulted from the joint work of Veitch and Lionel de Rothschild; ‘Taylori’, a pure pink; ‘Sir George Holford’; ‘Souvenir of J.H. Mangles’; R. brookeanum var. gracile, fluorescent coral-orange; ‘Pink Seedling’; and ‘Pink Delight’. But vireyas were much too beautiful to be forgotten forever. In the late 1930s, the director of the Singapore Botanical Gardens, R.E. Holttum, believed vireyas were suited to the hot, humid climate of his city and began collecting them from Malaysia. War again interfered. When the Japanese invaded Malaysia at the outbreak of World War II, Holttum’s pursuit of vireyas ended and all of his hybrids were lost.
Interest revived in the early 1950s, perhaps as a result of Westerners being drawn into the Malaysian forests in the name of war. Botanical expeditions followed. The German Hermann Sleumer, who had studied Vireya rhododendrons systematically for many years, undertook an expedition in 1961, of which the American Rhododendron Society was a sponsor. He introduced hundreds of new species that set the base for the current popularity of vireyas. The National Arboretum in Washington, D.C., had the foresight to acquire some of the British plants in the early 1950s. These were propagated, and in 1961 plants were made available in limited numbers. Some came to the Strybing Arboretum in San Francisco, and these, with Sleumer’s species, and others from friends of the arboretum in Australia and Great Britain, were used to develop new plants suitable for the San Francisco Bay Area. Progress at Strybing was such that by 1969 plants could be sent to several interested California growers. It was as well that this was done, for in a few years most of the plants at Strybing Arboretum were destroyed.
Most of the vireyas were planted on a normally frost-free hillside in the arboretum. On a night in December 1972, the temperature unexpectedly dropped to 23° F. and remained below 32° F. for some time. The plants on the hill were lost; only those in greenhouses were saved. Many lost heart and interest in vireyas waned, but at Strybing Arboretum the collection was rebuilt. Many of those who had received plants from the Arboretum in 1969 were able to send cuttings or young plants back again. Several amateur rhododendron enthusiasts in the San Francisco Bay Area helped and eventually hybridization of vireyas began again at Strybing Arboretum.
Once again material for propagation flowed from the Arboretum to those anxious to experiment with vireyas. In Southern California, where the climate seems more suitable for vireyas than for most other rhododendrons, enthusiasts in the Southern California Chapter of the American Rhododendron Society had help and advice on growing them from the Strybing staff and many of them have since made their own contribution to the study and hybridization of vireyas.
In 1976 the collection of vireyas at Strybing was hit again — not by the weather, but by a strike of city employees among whom were those at the Arboretum. During the difficulties that ensued several vireyas were lost through theft and vandalism.
Despite the many difficulties, vireyas are finding their way into commerce and they now seem destined to stay there. Plants suitable for growing indoors in pots, and others for use outdoors where the climate is mild, are available.
Among those available is a hybrid with flowers of orange and yellow that resulted from a cross between Rhododendron christianae, with small, red-yellow flowers, and R. laetum, which has the richest and purest yellow flowers of any in the genus Rhododendron. There is another with flowers of similar color, raised from a cross between R. christianae and R. macgregoriae which may prove to be hardier than most. ‘Red Prince’ is one of the surviving Victorian hybrids. It has deep pink flowers and unusually compact foliage. Crosses between R. Iochae and R. javanicum have given a compact plant with bright red flowers that is especially suitable for use in hanging baskets. ‘Princess Alexandra’, with snow-white flowers, was raised a hundred or so years ago from ‘Princess Royal’ and R. jasminiflorum. ‘Sybil’ has pink flowers and is another of the survivors from the past. More are being developed.
Their natural habitats give us guidance in cultivating vireyas. Some vireyas are epiphytic and are found in the mossy boughs of trees; others are terrestrial in the savannas and grasslands of New Guinea, Java, Borneo, Sumatra and other islands of the Malay-Indonesian archipelago. In their tropical homes, they experience little year-round seasonal variation in temperature and daylight, but the monsoons bring intense rainstorms and long dry periods. With this in mind the best treatment for vireyas in cultivation will be easy to recognize. Commercial growers in the West suggest the following methods.
To grow vireyas as houseplants, use containers that can be easily transported. Keep them in a sunny southern windowsill or in a well-lighted room during winter months and move them outdoors after danger of frost is past. Return them to the house when fall temperatures again begin to drop to the low 40s. Vireyas are excellent for patios and porches. In Southern California heat waves occasionally cause sharp humidity drops and growers there may need to use pots larger than usual to help keep the soil moist.
As bedding plants in landscapes for mild winter areas, such as Southern California, vireyas are best on the north and east sides of the house. If your region is subject to hot, dry, summer winds, shelter the plants with windbreaks. Screens of tall plants able to withstand wind will retain moist air near the vireyas. Should you plant on the south and west sides of the house, protect the plants from hot late morning and afternoon sun with filtered shade from trees, laths or shade cloth.
Vireyas are generally best in raised beds two feet wide and fifteen inches deep, or in large pots and tubs. The growing medium should be a soil-free mix that is acidic and porous. A loose, well-aerated medium that allows quick drainage can be mixed from equal parts of screened five-eighths-inch bark — redwood, hemlock, or fir (this is sold as orchid bark); coarse peat moss (greenhouse grind); and coarse perlite. Do not use packaged orchid mixes, bromeliad mixes, super-soil, or azalea planter mixes, and avoid finely ground peat.
Ideal light conditions are direct sun from sunrise until 11 A.M. and filtered sunlight thereafter. Fluorescent lights can supplement natural light indoors. If humidity is high and your climate is generally cool, vireyas can tolerate more direct sunlight. The closer you are to the equator, the more need you may have for sunlight-filtering devices. A 60 percent shaded lath cover, or 55 percent polypropylene shade cloth can be used where no light is filtered by trees.
Never allow vireyas to freeze; however, they will tolerate short periods down to 30° F., some even to 25° F. They can stand summer temperatures of 105° F. or more, with proper humidity. Average temperatures should vary overall 10° to 20° F. from summer to winter with an average daytime temperature of 70° F. and an average nighttime temperature of 45° F. On the other hand, some experienced growers report that when grown as houseplants, better performance is achieved if they are in rooms where the greatest variation in temperature — night to day — is allowed.
Vireyas perform well out-of-doors in areas designated in Sunset Garden Book as climate zones 21, 23 and 24. They need protection from occasional freezes in zones 16, 17 and 20. They perform best in cool greenhouses where relative humidity can be kept above 20 percent and where they have protection from temperatures below 30° F. in zones 18 and 19. Vireyas have been grown outdoors in zones 18 and 19, but low humidity restricts their performance there.
Keep plants on the dry side but increase watering during major flowering periods, usually between October and March, and while plants are very young. Avoid a continually soggy mix. Water thoroughly and then withhold water until the medium is light and dry again. Water early in the day and do not mist houseplants often as moisture in static air encourages mildew. Fertilize several times in spring and early summer, and shortly after flower buds first appear, with a half-strength, or less, solution of fish fertilizer or liquid fertilizer such as Rapid-Gro or Peters. Dilute the fertilizer even more if foliage shows signs of damage. (Southern California Chapter of the American Rhododendron Society has developed a special formulation for vireyas which overcomes the alkaline water conditions peculiar to that region. This fertilizer is available to chapter members.)
Prune and pinch young plants to encourage bushy growth. From the time plants are a few inches high until they are two-and-a-half years old, pinch out any single apical buds as they begin to elongate. Buds begin to form nine months ahead of flowering so you may prevent blooming if you delay pinching. To prune plants older than four years, establish a routine of cutting out a third of the plant each year. Cut branches that have flowered back to the lowest healthy rosette of leaves.
Mulching the surface of the soil, outdoors or in pots, retains moisture and keeps roots cool. Use the longest needles of spruce, cedar or pine trees — avoid the short, fine ones — or use coarse bark.
While vireyas seem safe at last in the United States, they are now threatened with extinction in their native habitat. In removing the trees, timber harvesters are destroying 280 kinds of rhododendrons in Indonesia and Malaysia as they move across broad tracts of tropical forest. Great increases in population in tropical countries are creating demands for food production that accelerate the destruction in the forest. Information on this was given by Dr. W.L. Theobald in Pacific Horticulture, Summer 1980. The U.S. National Academy of Science pointed out in July 1980 that all tropical forests will be destroyed within the next fifty years at the present rate of exploitation. Perhaps the lowered thermostats and reduced yard space of American homes, along with intelligent propagation and hybridizing, will insure a place for vireyas. To see them is to know that they are too lovely ever to be lost again.