Species In Our
Rhododendron sargentianum is a dwarf lepidote species from the high elevations of Sichuan, China. E. H. 'Chinese' Wilson, while plant exploring for Veitch and Sons, first introduced it in 1903-4. He found it again growing on exposed rocks and cliffs in 1908 and 1910, naming it in 1913 after C.S. Sargent, director of the Arnold Arboretum. It has not been collected since. R. sargentianum is in the subgenus Rhododendron in the section Pogonanthum. The Pogonanthum section is full of wonderful species that are amazingly hard to grow in New England. Like other members of this section R. sargentianum dislikes hot summers, requires excellent drainage with a lean soil mix, and performs better at a higher pH than most rhododendrons.
The small leaves, less than an inch (2.2 cm) in length, are elliptic to oval in shape with a shiny dark green upper surface and a rusty lower surface colored by the 2-3 tiers of overlapping scales. The bud scales are persistent on the stem. A close inspection will find the flower bud scales fringed with large branched hairs. The flowers are a soft yellow, cream to white in loose clusters of 5-12. The corolla is daphne-like with a narrow tube 1.2-2.3 cm long sharply opening to spreading lobes. The pistil and 5 stamens do not extend beyond the tube. Its habit is dense, low and mounding, growing slowly to 1 foot by 1 foot in 10 years. It is reportedly relatively free flowering when happy and frequently receives awards in shows on the West Coast and Great Britain, blooming about early mid-season there. It is rated to -5°F (-20° C), sometimes to -10°F (-23°C), but cold hardiness is not as likely to kill it in the garden as much as summer heat.
The three named forms are: 'Liz Ann' (a pale pink), 'Whitebait' (a cream yellow), and 'Maricee' (a cream white that may be a hybrid). There is only one registered hybrid, 'Sarled' which is a cross with the closely related species R. trichostomum Ledoides Group, rated at -10°F. The hybrid, R. sargentianum x R. myrtifolium, is grown in England.
The genetic variability of R. sargentianum, based on selections made almost 100 years ago, is probably very limited. It would be worthwhile to collect seed in the wild again for diversity's sake, and maybe to get a more heat tolerant clone. I acquired a seedling from the ARS conference in Vancouver, Canada, in 1999. It has grown well but has not flowered in Salem, NH. The plant is not quite as compact and tight as I would have expected, but then I do not grow it in the full sun that it prefers. Knowing more about who is growing this species in New England and where, and how successful they are would be an important addition to the Species Study Group database.
Sally Perkins, Salem, NH.