Elepidote Rhododendrons at Winterthur
Hal Bruce, Winterthur, Delaware
Thirteen years have passed since Winterthur hosted the annual meeting of the ARS (See ARS Bulletin, Vol. 16, #1, 1/15/62). Since that time the world has changed a great deal. At Winterthur, several decades of constant experimentation and introduction of new plants have ceased with the death of Henry Francis du Pont, its founder, in 1969. Yet today the gardens here seem as serene and untouched by time and change as they always have, a fitting monument to a life devoted to horticulture.
I use the word "seem" deliberately. As every gardener knows, plants are not static entities: they grow, they spread, they malinger, they die. Pictures painted with landscape materials need constant revision or they change for the worse. Today all maintenance at Winterthur is directed towards the preservation of the gardens as H. F. du Pont envisioned and created them.
Sometimes this has not been easy. Azaleas have grown out of bounds en masse, requiring brutal pruning back to prescribed heights. Wild dogwoods and viburnums have encroached on delicate exotics and threatened to smother them. Wind, rain, and lightning have brought down huge trees irreplaceable within a hundred years. And age has taken its steady toll of forest trees and exotic ornamentals alike. The scale of these gardens is so vast, however, and so rich in resources, that the attrition rate is comparatively low. Visitors probably never notice the reparations.
Thinking of this, I was struck by the thought of how constant and permanent large-leaved rhododendrons are in the landscape. We have lost a very few to age - not many - and replaced them with younger specimens from the nursery. A few have been damaged by falling branches. But none has required pruning, and indeed few have changed significantly in height, proportion, or overall appearance since Mr. du Pont died. This applies in particular to older plants. For example, there grows in the Azalea Woods a specimen of R. fortunei which as far as we know came from the estate of C. S. Sargent in 1927, as a plant of flowering size. Its annual growth is quite minimal, yet it blooms well each year and bears healthy and vigorous foliage. It looks to me exactly as it did when I first saw it in 1959.
Now, as thirteen years ago, rhododendron contains more representatives at Winterthur, both in terms of species and hybrids and in terms of individual specimens, than any genus of the plant kingdom. Of these, the elepidote rhododendrons play a very important role. Since nothing has ever been published in depth on their use and performance here, I should like to consider them in some detail in this article.
The climate at Winterthur is typical of the East, with cold winters and hot summers. Winter temperatures are mild compared to, say, Boston, but occasionally the thermometer registers zero degrees F., and every ten or fifteen years we experience a period during which it dips below that. Summers are usually humid, but punctuated by periods of drought and extreme heat which do as much damage to plants as winter cold. Rhododendrons from inland China and the Himalayas suffer greatly from this combination of fluctuating winter temperatures and summer heat and drought. The easiest elepidotes to cultivate are the two which are adapted to the climate: R. catawbiense and R. maximum and their derivatives. We find also that R. fortunei from eastern China is hardy and adaptable, and that most hybrids with a generous proportion of its blood will succeed here.
This is not to say that we have no success with any of the exotic species. One of the first big spring displays consists of a combination of central Chinese rhododendrons: R. sutchuenense and its presumed hybrid 'Geraldii' with another Fortunei-series species purchased from C. O. Dexter as R. praevemum but identical to the seedlings of R. oreodoxa forma haematochilum disseminated some years ago by Joseph Gable. These bloom sumptuously in April, so early that their flowers are frequently frozen at night. Their fat pink buds opening to paler, deep-blotched bells are extremely showy in the dark, naked, wintry woodlands, where the first wildflowers are only beginning to show themselves.
At the end of April R. fortunei opens its large, pale mauve, sweetly-scented flowers with the earliest of the Dexter Hybrids and Kurume Azaleas. A week or so later another member of the Fortunei series blooms with large apricot-pink flowers which resemble those of many of the Dexter Hybrids, fragrance and all. This is R. vernicosum Rock 18139, (See cover photo) purchased from Joseph Gable in the early '60s, and not conforming to the botanical description of the species in habit, foliage, or flower. In 1962 Mr. Gable told me that neither he nor David Leach thought it was R. vernicosum but neither could classify it exactly. It is a very ornamental plant.
A word here on soil and terrain. Winterthur is located in the Piedmont of northern Delaware (USDA Zone 7a), a region of rolling hills separated by valleys through which streams which originate in the mountains to the north and west run rapidly on their way to the coast. A few miles to the southeast begins the Coastal Plain, with its flat stretches of acid, sandy soil. Soils at Winterthur, however, are rocky and mainly clay, nearly neutral in reaction and quite sterile beneath a thin layer of humus. Most of our elepidote rhododendrons grow in an open woodland at the crest of one of the highest hills, called the "Azalea Woods". This includes the early display mentioned earlier as well as most of the Dexter Hybrids and other R. fortunei derivatives which bloom in early May. Also here are Kurume and Torch (R. kaempferi Azaleas), which bloom at the same time. A secondary rhododendron planting is located further down the hill closer to the Museum and reception building. This consists mainly of "Ironclad" hybrids along with late-blooming azaleas such as the beautiful R. mucronatum 'Magnifica.' Here bloom begins somewhat later, in the middle of May. Elsewhere in the gardens rhododendrons are less concentrated, being used mainly as punctuation marks in the landscape for such distinctions as unusual foliage effects or late bloom.
Two members of the Caucausicum Subseries bloom in May in the Quarry, well away from the main rhododendron planting, where their elegant foliage is an excellent foil to the rough rocks. R. yakushimanum, in the Exbury form, was bought from the Exbury estate in 1953. Although growing in consider able shade, it stands less than three feet high and blooms well every year. R. makinoi is somewhat disappointing in bloom, with ordinary and not very showy pink flowers. Its long narrow, heavily indumented leaves, however, are its chief attraction. Unlike R. yakushimanum, its flower buds are sometimes destroyed by either winter cold or spring frosts.
A third member of this subseries is another with some mystery in its background. It came from Gable as R. chrysanthum (now R. aureum), but promptly grew to five feet in height and bore white, not yellow flowers. Our investigations determined that it is the plant which Japanese botanists claim to be a natural hybrid between R. aureum and R. brachycarpum but which David Leach thinks is a full species, R. nikomontanum. Whatever its true status it is a good plant, quite hardy and bearing deep green convex leaves like those of a gigantic Ilex crenata convexa. Its flowers, which come in late May, rather later than those of the mid-season catawbas, are small, frilled, pure white with a green blotch, and borne in tight trusses.
Probably the easiest rhododendron in Delaware is the adaptable R. catawbiense, but as everyone knows, its muddy purple color is unattractive. The clone called 'Catalgla' is, however, very ornamental with its white flowers opening from lavender-tinted buds. It holds its own with most mid-season hybrids here and is considered a valuable plant. The only other elepidote rhododendron native to the East is R. maximum, which here is just as hardy and adaptable as catawbiense. It is a big, spreading plant whose flowers, though they lack the muddy purple tones of its relative, are small and not very showy. These are typically white, opening from bright pink buds, and since they appear very late in the season - on some plants not until the fourth of July - and are pleasing in color, the species has been spotted here and there throughout the gardens.
Like all gardeners, H. F. du Pont was concerned with extending the blooming season beyond the ordinary period by introducing plants which bloom earlier and later than usual. By 1946 he had discovered R. discolor and in less than ten years had this treelike species in bloom in the gardens. Today it is widely planted in the woodlands (where it does best), for its foliage is very fine, its large, pale lavender-pink flowers very showy, and its blooming season - early June - unusual. The oldest plant on the place grows in deep shade beside the H. F. du Pont House, where its enormous scented blossoms look into the second-story windows. A second late-flowering species came to Winterthur even earlier, for our records show that two small plants of R. auriculatum came from Joe Gable in February of 1933. One of these apparently died, but the other lived on a rocky bank near the museum until 1974, when it was destroyed by a falling branch. In all those years it had only reached about six feet in height (though it should have reached twenty, according to the manuals), yet regularly bore its big, white, trumpet-shaped flowers during the last week in July, the last rhododendron of all to bloom.
Some of the oldest plants on the place are ironclad hybrids whose names have long been lost. These today are enormous plants, most of which bloom in mid-May, though a few, their robust growth and late bloom perhaps indicating maximum heritage, bloom in June. Also blooming in June (and planted with the aforementioned late ironclads near the H. F. du Pont House) is a tall, white discolor type which we originally thought to be a white form of the species but now believe to be Gable's 'Disca'. If what we suspect is correct, it is certainly one of the largest specimens of this hybrid in existence. It grows in a bay between tree magnolias, backed by ancient hollies and a sheer wall of forest trees, and is absolutely overwhelming in bloom. Another Gable discolor hybrid growing here is 'Robert Allison,' or, as it was called in the old days, 'Pink #2'. This is also June-blooming, with large, bright pink flowers in huge trusses. It is hardy and adaptable, with much of its parent's robust constitution.
Any reader who has followed me thus far will be aware of how frequently the name "Gable" appears in these notes. The gardens here would be infinitely poorer had that great old man never lived. Everywhere one turns he encounters a Gable rhododendron or azalea, and every one of these is outstanding. One of H. F. du Pont's favorites was 'Caroline'. This is a plant of high quality - hardy, adaptable to adverse conditions, excellent in bloom and foliage. One of the few Gables whose parentage is uncertain, 'Caroline' is listed simply as a decorum hybrid, though it undoubtedly contains genes of discolor also, as its narrow, pointed foliage and fairly late blooming season (late May) indicate. It is a quietly impressive plant, whose good qualities become more evident with each passing year. The flowers are large, of a refreshing clear mauve, opening from deep rose buds. The foliage is dark and glossy, resistant to pests and diseases, each leaf with a distinctive wavy margin. Growth is vigorous and habit dense, even in shade. I understand also that it is noted as resistant to many of the rhododendron ills prevalent in the East. We use it in the Azalea Woods to bring color to the area after the main flush of bloom on the Dexters has passed.
'Atroflo,' a Gable cross of the old catawba hybrid 'Atrosanguineum' with R. floccigerum of the Neriiflorum Series, is an interesting if not perfect garden plant. It is tall and open in growth, even in sun, with long, narrow, heavily indumented leaves. Its blossoms are large, open funnel-shaped, in loose trusses of an intense pink-red. Its one fault is that it sheds most of its old foliage each year, resulting in an open, "bony" look. Although quite hardy with us, it does better in the protection of woodlands than in full exposure. I don't know whether anyone has as yet used it for breeding, but would think it a good bet for indumentum and red or yellow flowers, especially with some of the newer yakushimanum hybrids. It blooms in mid-May.
'Red Sox,' a brachycarpum hybrid, is a midseason red with convex leaves showing the conspicuous mid vein of brachycarpum, and dark lacquer-red flowers with no trace of purple. An added attribute is that its calyces are petaloid, giving a hose-in-hose effect. Unfortunately, with us it is not a thrifty grower, and its foliage tends to spot and discolor. We are not sure whether to blame plants or locations for this, though poor growth is reportedly a characteristic of many brachycarpum hybrids.
Two other red Gable hybrids which have excellent flowers are 'Kentucky Cardinal' and 'Redhead'. Like 'Red Sox' these do not do well in dense woodland where discolor and fortunei thrive. With more sun, however, they are fine.
One of Gable's best is 'David Gable' ('Atrosanguineum' x fortunei), a robust plant with magnificent, dark-throated blossoms of deep rose. Like most fortunei derivatives, it thrives in shade, but does well also in my own sunny garden. 'County of York' in a different way is just as showy. From one parent, 'Catalgla,' it inherits a good constitution. From the other, 'Loderi,' it gets its tall stature, large foliage, and large flowers. Its shining, convex olive-green leaves are unusual, and its flowers last longer than those of any white I know, especially since it blooms late in May when we usually have periods of intense heat.
In early May an un-named Gable cross, fortunei x 'Madonna', blooms with the Dexters in the Azalea Woods. We have several seedlings of this cross as well as a few of the reverse cross, and all bear fine big flowers of pale blush pink or white. With blood of decorum, griersonianum, and catawbiense (through the ironclad 'America') besides that of fortunei, this should offer excellent hybridizing potential. It is a superlative ornamental as well, one of the finest, in fact, that Gable ever produced.
The climate of the American East is of course unsuitable for many of the sumptuous hybrids produced on the West Coast and in England, but several do well in the Azalea Woods, where the trees and hilly terrain provide protection from frost damage, winter wind, and summer heat. An extensive sprinkling system no doubt helps enormously in getting these plants through summer droughts, but even extensive watering has not prevented losses due to the oppressive heat of Delaware summers. Derivatives of R. forrestii var. repens seem especially intolerant of heat here, such hybrids as 'Elisabeth Hobbie' and 'Scarlet Wonder' being total failures. Cultivars which have proved susceptible to winter cold rather than summer heat include the celebrated 'Crest,' 'Elizabeth,' 'Harvest Moon,' 'Countess of Derby,' and 'Moonstone'. The latter two persisted for several years but eventually succumbed. The fine red "Madame de Bruin', in spite of its H2 rating, also succumbed. 'Loder's White' promptly died in the sunny nursery, but one plant hangs on yet in the Azalea Woods.
Genes of R. fortunei seem nearly as effective in ensuring hardiness in our climate as those from catawbiense or maximum, and such hybrids of it as 'China' and 'Goldfort' do extremely well here. 'China' (wightii x fortunei) blooms in early May, a perfect companion to the Dexter Hybrids nearby. It is a big plant in every way, with flowers opening pink and passing through pale yellow to ivory. Its large leaves with distinctly impressed veins make it striking all year around. Our original plant came from Exbury in 1953 and is now about ten feet tall. It has been propagated extensively, the cuttings rooting easily under mist.
'Goldfort', which is also half fortunei, is an excellent companion to 'China.' It is also a large, robust plant, though its foliage is less interesting. Its flowers in early May are large and a clear, pale yellow in color. In full bloom it is a stunning thing. The original plant came from Jock Brydon in 1955.
Two further yellows should be classified in the borderline category here, but are so showy that I must mention them. 'Unique' has persisted for fifteen years, and with the recent cycle of mild winters lives up to its name. For the first several years, however, it suffered winterkill of branches and, of course, flower buds so much that we considered discarding it. Since the early '70's it has bloomed well, the compact, shapely plant studded with globes of pink-budded silvery yellow flowers. One can see why it is so highly rated. It has also the distinction of being the earliest hybrid in its class to flower (and certainly the first yellow), beginning in late April and anticipating by several days even the earliest Dexters.
'Carita', with an H4 rating, is surprisingly hardy here, though half the plant was lost in the bad winter of 1961-2. Our records show that a plant was purchased from Exbury in Nov., 1953 but died in June, 1954. The following year another was supplied by Jock Brydon. This first set buds in 1964 and has bloomed fairly reliably since. The clone must be 'Golden Dream', for it is a fine, clear yellow.
Another campylocarpum hybrid which seems hardier than the two preceding is 'Citronella'. One seldom reads about this old hybrid, but it is a very showy bright yellow with enough fortunei blood to make it successful in the East. Our plant has grown here since the 'fifties, but did not set bud until 1971, possibly because it was growing in quite dense shade. Growing near 'Citronella' is the red 'Princess Elizabeth', which is thriving but devoid of flowers. Again, I think this must be attributed to insufficient sunlight. Most of our reds seem more intolerant of shade than those in other color classes.
Turning from English hybrids to the named Dexter clones, we find a group which is much better suited to our climate. We grow 'Ben Mosely', 'Skyglow', 'Brookville', 'Betty Hume', and 'Scintillation', all of which are fine plants. The pink 'Betty Hume's' growth is most unusual. Our plant, a gift from David Leach at the AIRS meeting here in 1962, is presently about 5'/z feet tall by nearly 10 feet broad, with excellent foliage and density. 'Scintillation' is in a class by itself for foliage, habit and masses of flowers. It always reminds me of a pink hydrangea - almost too garish, until its many virtues and total lack of flaws are reviewed.
The great bulk of display from large leaved rhododendrons here comes from the un-named hybrids which H. F. du Pont bought by the hundreds as flatted seedlings from C. O. Dexter in the '30's. Few of these are ornamentally superior to the named clones mentioned above, but all fulfill their purpose in the landscape as enormous, floriferous specimen plants. Most fall in the pink or mauve range as to color, but there are a few reds and apricots, and one really lovely near-yellow.
These are numbered according to their sequence of bloom. Number 1 is usually the first in flower, in late April or early May, with a large fortunei-type flower of pink with an undertone of coppery yellow which registers as a bright peachy orange at a distance. Number 2 and number 7 are similar. Number 1 1 is one of the few reds, a fairly low plant with cherry-red flowers only slightly muddied by purple. This may be one of the few survivors of a flat of decorum x 'Cornubia' purchased in 1933. Probably the best of them all is number 6, a soft apricot-yellow, large-flowered, robust, and good in foliage, which has the distinction of being the only rhododendron that Mr. du Pont ever named. It is called 'Tan'.
Finally, there are two hybrids which fall into none of the classes mentioned so far, but deserve discussion if only for the fact that they bloom late in the season and thus extend the blooming period in the Azalea Woods. 'Lady Eleanor Cathcart' is an old hybrid of maximum and arboreum which, as the parentage suggests, is a tall and vigorous grower, ideally suited for the woodland. The long, narrow leaves are a good gray-green and the flowers appear around the first of June. These are comparatively small, in tight, many-flowered trusses, and are a fine shade of coral-pink, with no blue whatsoever. It is completely hardy and adaptable in our climate.
'Woodlawn' is even later in bloom, a fairly tall but densely-foliaged plant with rather small but very frilly flowers in tight round trusses. Its buds are deep rose red, opening to pale rose. The leaves are small, narrow, and very dark green. It is supposedly a dwarf, though our plant has reached six feet or more in ten years. I can find no information as to its parentage, but it is a pretty rhododendron of considerable value for
its early June blooming season.
We have found that the ideal way to establish rhododendrons is to grow them for a few years in a sunny nursery row in order to build up a good, compact branching structure before transferring them to permanent positions in the woods. We used to excavate enormous holes at their permanent sites and fill these with a mixture of peat and topsoil. Experience has taught us, however, that small holes at planting time make better plants at maturity, presumably because roots are forced into the surrounding unprepared soil when plants are young and vigorous.