JARS v37n3 - Rhododendrons In The VanDusen Botanical Garden Vancouver, B.C.

Rhododendrons In The VanDusen Botanical Garden Vancouver, B.C.
R. Roy Forster, Curator

The VanDusen Botanical Garden is one of the youngest gardens in North America. Construction began in 1971, and continues unabated at the present time. This decade of garden-building has been a period of intensive acquisition of plant collections. There has been some emphasis on Rhododendron , because of the popularity of this plant in the Pacific Northwest and the relative ease with which it can be grown. A wide spectrum of rhododendron hybrids are in the garden, ranging from the old, hardy "Ironclads" through the British hybrids incorporating the genes of Asian species during the golden era of rhododendron exploration, and the more recent, opulent, modern hybrids from the hands of North American hybridists. The rhododendron hybrid collection is laid out in such a way as to indicate parentage - the plants are in groups associated with specimen plants of the parent species. Such an arrangement is useful to students of the rich heritage of rhododendron hybrids. However, it is an artificial system - less interesting than more natural methods of garden layout. It was with this idea of naturalism in mind that the concept of a Sino-Himalayan Garden was born. This is the newest and largest component of the botanical garden. The excitement that was generated by the great natural beauty of the site was tempered by the knowledge that times of fiscal restraint lay ahead, and maintenance costs needed to be held to a minimum. A woodland theme was decided upon as best suited to this purpose and also the most aesthetically-pleasing setting for a large collection of Asian plants with the emphasis on Rhododendron .
The most satisfying and perhaps the most informative format is the type of garden or collection based on a geographical region, and such an opportunity exists in the concept of the Sino-Himalayan Garden. This project has great appeal because of the wide range of superior plants available now, and the exciting possibility of new introductions in the future. The garden will serve as a living herbarium of species that have been assembled in the past, and a testing ground for new material collected from the richest area for temperate plants in the world. To those building the garden and for those who will use it, there is the excitement of participating vicariously, or in a real sense, in the romance of plant exploration. The Sino-Himalayan Garden will contain a wide range of woody plant genera native to China and the Himalayan area. However, rhododendrons dominate the landscape, since this garden represents a montane theme. The theme is accentuated by the magnificent views from the garden to the nearby Coast Range Mountains - the peaks are snow-clad into the summer months.
The Sino-Himalayan Garden is the largest single component of VanDusen Botanical Garden. The landscape style is naturalism, since this is to be a woodland garden. However, at the present stage of development it must be admitted that most of the site is not wooded. With some supplemental watering in the summer months, and the moist climate at the Pacific Northwest, most shade-requiring plants will grow reasonably well with full exposure. Lacking a woodland, we have had to plant our own forest of young trees. Given good growth rates expected on the Pacific Coast, these trees will provide shade within five years, after which a woodland micro-climate will begin to develop. The need for supplemental irrigation will decrease and our maintenance task will be lighter. Meanwhile, the extensive Rhododendron collection in the new garden is heavily mulched with leaf mould to help soften the impact of the exposed conditions. The Sino-Himalayan Garden was built on top of the existing surface using large quantities of fill, soil, and rock. Within its boundaries are small valleys, a waterfall, streams, and an exposed, treeless bluff for the cultivation of subalpine plants. The physical profile of the finished site is a series of berms and intervening valleys.
The garden may be unique in that all its plant components are Chinese or Himalayan in origin - including those that will eventually form the tree canopy. This will give authenticity to the new garden. In terms of the range of species grown (hybrids will be avoided) the garden is essentially a rhododendron garden, enriched with a wide range of other Sino-Himalayan plants of many genera. We are fortunate in having at our disposal, one of the largest rhododendron collections ever assembled in North America. This is the Greig Collection, from Royston, B.C. acquired by the Vancouver Park Board in 1965 and until 1981, burgeoning in size and numbers in Stanley Park, Vancouver. Originally, the collection was not acquired for the botanical garden rather it was seen as an embellishment of the delightful woodland in Stanley Park. However, it seemed natural and logical that the collection should find a permanent home in the botanical garden where it can be systematically recorded, labeled, and displayed to the public.
Our roughed-in Sino-Himalayan Garden met with the approval of Alleyne Cooke, the curator of the Greig Collection, and he began moving some 2,000 plants to the new site in the autumn of1981. Over 250 species and subspecies are represented. In addition, another group of plants were acquired from the Rhododendron Species Foundation. Despite the temporary absence of shade, early indications are favourable and very few plants have been lost. Growth is firm and compact, which augers well for well-shaped floriferous plants in the future. The lepidote species exhibit the slight bronze" pigmentation that develops under exposed conditions. During the winter, the dwarf lepidote subalpine species such as R. hippophaeoides turned almost black, but soon turned green with the arrival of spring.

The large-leaved Himalayan species such as R. macabeanum and R. sinogrande are placed under the shade of a small grove of Douglas Fir. The statuesque March flowering R. calophytum is also given some shade and protection because of its large vulnerable leaves. Yet this species, when properly sited, is apparently the hardiest of the tree-like species of Rhododendron, reaching as it does, an altitude of at least 2500 M in Sichuan. Another fine and large species, the July-flowering R. auriculatum also requires protected woodland conditions, both from the point of view of hardiness and to protect the flowers from the mid-summer sun. All these plants were moved from a well-sheltered, moist, shaded environment at sea level in Stanley Park to a more exposed site subject to strong winds. Wind damage at times has been severe. R. hemsleyanum , a rather large-leaved species in the subsection Fortunea, was almost defoliated by wind during the winter. The new crop of leaves are smaller and it will be interesting to observe if the species can adapt to the new planting site. This species is endemic to Omei Shan, in S.W. Sichuan, visited by the writer in 1981. At 29° latitude, and under 1,400 M altitude, this habitat of R. hemsleyanum is a mild area indeed even when compared with gentle Vancouver! Vancouver's latitude is 49.5° N. The average July temperature is 17.4° C (63°F). The average January temperature is +2.4°C (36°F) and the lowest temperature recorded (1968) was -17.8°C (0°F). To complete these statistics, the average annual rainfall is 127 cm (50"). Most of this precipitation comes in the winter (as rain) and summer droughts are not uncommon.

The construction of the Sino-Himalayan Garden began in the summer of 1979 and continued through to 1981. When the earth moving and rockwork were complete, an irrigation system was installed. This proved to be the salvation of the project in the spring of 1982 when five weeks of dry, hot weather intervened during the critical season of growth.
Of these trees planted for shelter and shade, the conifers, Pinus wallichiana and Cedrus deodara are planted on the top of the earth berms. This device will increase the apparent height and emphasize the hoped-for effect of ridge and valley. Liriodendron chinensis , Quercus acutissima , Tetracentron sinensis , Castanea mollissima , Sorbus hupehensis , Magnolia sargentiana var. robusta , Acer grosseri , Acer griseum , Davidia involucrata and many other deciduous trees are distributed at random throughout the garden to provide shade. In the higher elevations, a few sporadic plants of Picea likiagensis , Picea brachytyla and Abies koreana have been added. In the lower sheltered valleys Cunninghamia lanceolata , Cupressus duclouxiana , and Cryptomeria japonica are found, and in the most sheltered place, the Chinese Windmill Palm, Trachycarpus fortunei . Climbers have not been forgotten and include Clematis montana and various species of Actinidia and Rosa . Some of the most delectable flowering shrubs are Chinese or Himalayan, such as Stachyurus chinensis and Hydrangea sargentiana - with enormous "furry" leaves and large blue "lacecap" flowers. Hibiscus syriacus , Mahonia bealei and Rosa chinensis are also liberally planted in the garden.

The rhododendrons are arranged in their subsections. This method tends to favour the planting of large drifts of one species adjacent to groups of other closely-related species. For example, an entire hillside is covered with Triflora rhododendrons, including R. augustinii , R. trichanthum , R. ambiguum , R. lutescens , and R. yunnanense . The landscape effect given by this hillside of several hundred "trifloras" is intriguing - the fine-textured effect is quite different than massed large-leaved rhododendrons. On the upper slopes of this same hill, the "trifloras" give way to drifts of Lapponica subsection rhododendron such as R. impeditum , R. fastigiatum and others, which gives a feeling of the great alpine drifts of these dwarf lepidote species in the montane areas of Western China. On a lower slope, a short distance away, is a large drift of Cinnabarina rhododendrons, which includes a selection of the many forms of R. cinnabarinum now lumped together under the subspecies of that name and R. cinnabarinum ssp. xanthocodon .

This method of planting species in large drifts is closer to the reality of nature than the single specimen or group planting often found in species collections. The writer has observed the extensive thickets of rhododendrons in the mountains of S.W. China. Closer to home, many rhododendron growers have had the opportunity of observing thickets of R. macrophyllum and R. occidentale in the Pacific Northwest. The latter species, in particular, is so variable that a large group would be required to even begin to express the range of variation, while it is impossible to duplicate these plant associations, an attempt at simulation can be made in large gardens. Admittedly, a great amount of space is required but the method makes possible the cultivation of a large number of variants within each species group. The kind of observations made by Alleyne Cook on R. forrestii can be made on other species in a very direct manner, because of the proximity of the plants. The method also has merit as an educational tool and is useful to rhododendron collectors who may wish to observe the variation within a species.