Although the rhododendrons with the larger flowers and leaves will be the mainstay in our gardens, there are other forms that also deserve a definite place, and high on my list, are the triflorums. They are a series mainly from Yunnan and Szchuan in south east China, which grow at an altitude of from seven thousand to thirteen thousand feet on cliffs and open hillsides, in a climate generally dryer than that in which the larger leaved rhododendrons grow. These usually are compact, medium to small, mostly evergreen shrubs, though some are deciduous They have many trusses of flowers, often several to each terminal, with only three flowers to the truss in some species, while others have a well rounded truss. The flowers are seldom over an inch and a half across. The white, pink and lavender flowers often have red spots in the throat, and the yellow ones have green spots. They are apparently quite hardy as I have several plants from six to eight feet high, and have never noticed any damage from cold with temperatures down to 5° above zero. They also seem very tolerant of the sun, most of them being planted in full exposure and apparently enjoying it.
Although there are approximately fifty species in this series, I am familiar with only a few, though probably the best. Some are mediocre. All are variable from seed, and even in the best of the species, a large percent are not desirable, thus necessitating a thorough culling for the best forms. This group contains some outstanding yellows, some often deeper colored than the. larger flowered types. Among them are R. keiskei , a small compact plant with clear primrose colored flowers with red anthers. This species is from Japan. R. lutescens , an upright grower, is especially nice with long pointed leaves. The new growth is a bright bronzy red, in itself a nice characteristic. The flowers are a rich yellow in the better forms, but, as in other yellows of this series, some are billious greenish color, and these should be avoided. Other yellows in this series highly regarded are R. ambiguum , R. hanceanum and R. xanthocodon , which has flowers shaped like a thimble, yellow, sometimes shaded toward orange. One of the better whites, is R. vilmorinianum , sometimes called the "white R. augustinii ," which has ochre spots in the throat. R. caeruleum , though usually pinkish, sometimes has white forms. The better forms of R. exquisitum are a fine pink with blue green roundish foliage. The outstanding triflorum in this garden, however, is davidsonianum , a rich clear pink with red spots in the throat. It is truly a beauty. Beware, though of the muddy pink forms of this species. R. yunnanense , white, pink or soft mauve is considered by many to be the best of the triflorum series. R. oreotrephes , a mauve to mauve pink; which I suspect prefers shade is good in its color, as is R. chasmanthum , a lavender rose. Also sometimes near this color is R. augustinii , which at its worst is a magenta, dingy pink or plum color, but at its best, one of the finest blue of all the rhododendrons. This sometimes has olive spots in the throat, and at other times yellow. When first open the color of R. augustinii is a a little hard, but after it has been open a few days, it changes to a soft, smoky blue. It is very outstanding, planted with other rhododendrons of contrasting color. In the deep purple, R. polylepis , R. pseudoyanthinum and R. apiculatum are reported to be good.
Although not of the R. triflorum , but the R. heliolepis series, R. rubiginosum , a mauve to rose purple color with deeper spotted throat, gives a similar appearance of habit and flowers, but blooms with the daffodils, camellias, and primroses, lengthening the blooming season considerably.
Kingdon Ward states, "One cannot go wrong with these triflorums ; they look good from anywhere, grow easily, flower freely, and give satisfaction always."