The Asian Influence in My Garden (continued)

Rhododendron Species

If I had to choose a favorite rhododendron in my garden, it would have to be the Japanese species Rhododendron metternichii. Although I have several forms of metternichii in my yard, the specific plant I so admire is a beautiful specimen which is perhaps 25 years old now, and measures 8 feet high by 10 feet wide. It boasts the most perfect, shiny, deep green foliage of anything around, and the underside of the leaf has an attractive tan felt called indumentum. The lushness of the foliage effect is enhanced by the fact that the leaves persist on my plant for almost five years. My garden has experienced some rather severe winters over the years with temperatures as low as 17 below zero, and not once have I ever noticed leaf burn or freeze damage on this plant. Even after the 1995 summer's extreme drought where so many plants were killed or suffered dieback, my metternichii showed no adverse effects.

R. metternichii
In April, metternichii covers itself with glorious trusses of clear pink flowers which always manage to escape the occasional late frost. The only flaw I have found with my plant is that it sets seed too easily, probably crossing with itself in much the way that our native R. maximum does. If I forget to "dead head", or remove spent flower trusses immediately after blooming, the plant still grows vigorously, but wastes too much energy producing seed and does not bud up well for the following season. Thus it tends to bloom well on alternate years. I have raised my metternichii from a small plant selected from a flat of seedlings shared with the Potomac Valley Chapter ARS by George Ring, past President of the ARS, many years ago. Thank you George.

Closely related to R. metternichii are two other Japanese species which I count among my favorites, R. makinoi and R. yakushimanum . Makinoi is a striking foliage plant, with very narrow leaves sometimes measuring over 5 inches long but usually less than 1/2 inch wide. The foliage is heavily indumented, and the new growth makes a commanding landscape statement throughout most of the summer. At first, the new shoots look like fuzzy white candles as they emerge in June. Gradually, the color changes to tan as the growth expands during July and August. Eventually, the fuzz on the upper surface of the leaf rubs off exposing a deep green leaf surface beneath, but the fuzzy tan indumentum remains on the underside of the leaves. The light colored whorls of narrow pointed leaves which contrast against the deep green foliage from previous years reminds me of a 4th of July fireworks display. I have raised several makinoi plants from seed as well as cuttings. My best plant is rather compact even though it is growing in rather deep shade and measures only 3 feet high by 4 feet wide in 25 years. I raised this plant from seed obtained in the ARS seed exchange. The flowers of most of my makinoi plants are deep pink and appear in early May, although there are clones which are blush pink to near white.

	R. makinoi flowers A nice pink form raised from seed	R. makinoi plant near my waterfall.
R. makinoi plant Long narrow foliage.

In its native environment, Rhododendron yakushimanum has a very limited distribution, found only on the northern end of Yakushima Island, a small mountainous island off the southern coast of Japan. This dwarf species was first described in 1921, and then introduced to western gardens after 1947 when it became the rage when exhibited at the Chelsea Flower Show. There is significant variation in foliage forms of R. yakushimanum, which is very noticeable when the plants are young. However, after attending two ARS conventions in Portland Oregon, I have observed that mature plants in the Cecil Smith Garden which were very distinctive in foliage forms in 1985, appeared more uniform when I toured again in 1995. My original yakushimanum plants which I raised from seed have not had the luxury of maturing gracefully, since they have been over run by more robust plants in my yard.


Yaku Angel A form of R. yakushimanum	R. yakushimanum plant An excellent dwarf rhododendron.

There are many selected forms of R. yakushimanum, some of which are probably hybrids and not pure "yak", but they all make excellent landscape subjects. My favorite clone right now is "Yaku Angel" which is a faster grower than the "Exbury" or "FCC" forms. The foliage is recurved, deep green above with heavy tan indumentum below. The leaves are longer and more narrow than most yaks, somewhat reminiscent of R. makinoi. The flowers of Yaku Angel are pink in bud but quickly turn to white as they open. Two other yaks which make excellent landscape subjects are "Mist Maiden" and "Ken Janek". Although both forms have been listed as varieties of the species, most horticulturists consider them to be hybrids. The plants are larger growing than typical yaks, and Mist Maiden is white whereas Ken Janek is blush pink.

I have raised many seedlings of primary yak crosses, and I especially like the cross (yakushimanum x R. metternichii) which produces uniformly compact plants with glossy leaves and blush pink to white flowers. These plants are exceptionally rugged, and have survived drought, heat, and cold. Seedlings have rolled around in pots in my back yard for years before I finally decided to give them a home. Another cross with an interesting foliage effect is (Yaku Angel x makinoi) whose plants have deep green narrow leaves, intermediate between the two parents. The flowers are pink in bud fading to white as the blossoms open, which is generally true for most primary yakushimanum crosses. Pale flower color is dominant in yakushimanum hybrids, but I am partial to white so I don't mind. Excellent foliage is dominant too.

China has so many superb rhododendron species that it is impossible to do them justice in a short article. Most of our modern hybrids, especially those with large flowers and strong colors have been developed from the wealth of species found in China. I have tried raising many exotic Chinese species, such as the yellow R. wardii, red R. griersonianum, and blue R. augustinii, but our winters are usually too cold and our summers too hot. The plants usually succumb to bark split, dieback, and disease problems. However, hybrids of these delicate sorts when crossed with hardier species are often very successful in our area. Perhaps the most adaptable Chinese rhododendron species and a proven parent for hybridizing here in the eastern United States is Rhododendron fortunei. It was named for plant explorer Robert Fortune who introduced the species in 1856. Fortunei is a tall grower with large leaves and large fragrant flowers which are usually pale lavender to near white. The plant is both cold hardy in our region as well as heat tolerant. This species is considered a likely parent of many of the Dexter rhododendrons, and seems to impart both large flower size and reasonable hardiness to its progeny. In contrast to the color dominance of R. yakushimanum, R. fortunei allows other colors to take precedence over the less desirable lavender tones. For instance, the best yellow rhododendron in my yard is the hybrid "Golden Star", a cross of R. croceum (considered a form of R. wardii) with R. fortunei. Given a moist but well drained location, this hybrid developed by Donald Hardgrove on Long Island has proven very reliable for me.


R. fortunei, white form A hardy species from China.	Scintillation A Dexter hybrid	Golden Star A Hardgrove hybrid

The Asian Influence in My Garden

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