Azaleas of the Obtusum Subseries at Winterthur
by Hal Bruce, Garden Taxonomist at Winterthur
The gardens of Winterthur are justly famous for azaleas. For most people this means the vast planting of Kurume Azaleas in the area known as the Azalea Woods, but even the most casual of visitors soon discovers that azaleas of many diverse types are used in nearly every part of the garden. Of these, "the evergreen azaleas" (those that belong to the Subseries Obtusum) are far and away the most important.
As most azalea specialists know, this group is for several reasons difficult to write about. First, it is an absolute nightmare of nomenclature on every level. Two of the most important species from a gardening point of view, R. obtusum and R. mucronatum, are probably not species at all, but garden hybrids cultivated for centuries in Japan before their introduction to the West. Further, the true R. indicum was hopelessly confused with both R. simsii and mucronatum during the early years of azalea introduction, and probably contributed little to the so-called Indica Azaleas common in the warmer parts of this country. The white form of mucronatum is still known as "indica alba" in nurseries. Finally, the Kurume "hybrids" may not be interspecific hybrids at all, but merely forms of the species obtusum (if it exists) or kiusianum. All this confusion is compounded greatly by the fact that there is an enormous number of cultivars (too many, in my view) in cultivation, with new ones every year being introduced.
We do not know when the first of this subseries was introduced to Winterthur, but we do know that some of the plants we now regard as stand-bys in the garden have grown here for sixty years or more. A notation in one of H.F. du Pont's garden diaries mentions a "big white azalea" (R. mucronatum?) as being planted out in the garden in the spring of 1910. Old bills show the purchase of R. obtusum amoenum in 1926. At about the same time R. kaempferi first appeared here. In 1917, Mr. du Pont purchased his first Kurumes at Cottage Gardens Nurseries on Long Island, and sometime between 1907 and 1917 he obtained R. mucronatum 'Magnifica' from the same firm. At the beginning of World War II he was growing the new Glenn Dales and a few Satsukis, and not much later he was growing Gable hybrids, for in a letter dated April 19, 1954, he invites Mr. Gable to Winterthur to see his own hybrids in flower.
It would be no exaggeration to say that during the first half of this century H. F. du Pont tried just about every new evergreen azalea that became available. Some of these the climate of Winterthur promptly eliminated. Others were discarded as inferior ornamentals. Nevertheless, the species, clones, and hybrids of evergreen azaleas grown at Winterthur today number about 250, and this, of course, does not include those old cultivars whose names have been lost. Space will not permit discussion of all of these, but I shall try to mention all that we consider of unusual merit.
Unless the Kurumes are considered pure obtusum, the only form of this doubtfully valid species that we are sure grows here is R. obtusum amoenum. Much maligned for the coloration of its magenta-purple blossoms, this variant is an excellent ornamental when used properly - that is, in situations where its strident color does not clash with the colors (many equally strident) of other azaleas, especially those in the "hot" red and pink range. The big old amoenums at Winterthur are surrounded by green lawn and big trees on a hillside below the Peony Garden. As one climbs away from them into the Peony Garden, he sees an echo of their magenta purple in the blooms of a very old clone of Moutan tree peony. The effect is very pleasing. The habit and foliage of amoenum, incidentally, are superb. It is one of the most truly evergreen of the group, with tiny, glossy leaves on a twiggy, billowing plant reminiscent of boxwood.
R. kiusianum (R. obtusum japonicum), now regarded by many as the predecessor of the Kurumes, is with us a dwarf, spreading, nearly deciduous plant with rather dull mauve flowers in early May. It is good for the rockery (there are three ten-year-old plants in the Quarry here), but not very effective in a large-scale landscape.
A third member of this complex is the Torch Azalea, R. kaempferi (or R. obtusum kaempferi). Horticulturally, there is no mistaking this species with any other. It is tall, almost tree-like in growth, eight to ten feet in height at about fifty years of age here, with two or three strong cinnamon-brown trunks and an abundance of horizontal branches. Here it is almost totally deciduous, so that its masses of powder-pink to salmon-red blossoms on leafless branches give an effect more like peach or cherry blossoms than azaleas. A large section of the Azalea Woods is planted with this species alone. The visitor walks along a tanbark path with veritable walls of dazzling flowers on either side of him before moving out into the more open, vista-laden area planted to the Kurumes. This species is one of the hardiest of the subseries. Its only drawback is that in strong sunlight its flowers bleach or burn to white at their edges. Since it is certainly at its best in the woodland, however, this need not be a drawback. R. kaempferi has a long history at Winterthur. We know for certain that Mr. du Pont purchased 200 plants from C. O. Dexter in 1930, but the species was probably growing here earlier, since correspondence with E. H. Wilson in the twenties is full of references to it.
The earliest species of this subseries to bloom here is the Korean Azalea, R. poukhanense. This is a robust plant, semi-deciduous like kaempferi (and just as hardy), but spreading rather than upright in habit. Its flowers are large - two inches or more in diameter - and of a clear lavender with a darker blotch. Its foliage is long and narrow, a pale green with silvery pubescence when young which provides a quite beautiful contrast to the flowers. At Winterthur it grows with a lepidote rhododendron, the pale yellow R. keiskei which blooms at about the same time in late April. The two together make an excellent color combination.
'Magnifica' is probably used
more frequently in Winterthur
plantings than any other azalea
Photo from Winterthur
In the middle of May, as the Kurumes are passing, R. mucronatum and its variants begin to bloom. These are all spreading bushes with large, gray-green, hairy and sticky leaves and very large flowers. They do best here with considerable sun, blooming sparsely and becoming leggy in dense shade. The ordinary white form (the old "ledifolia" or "indica alba") grows in full sun at the edge of the Sundial Garden. This is still, in my view, one of the best white azaleas in existence, in spite of the fact that every few years someone introduces a hybrid that is supposed to supersede it. 'Magnifica' is a bigger plant in every way, with enormous white flowers blotched strawberry pink. It is scattered throughout the gardens - probably no single clone of azalea is used so extensively here as this. One group on a bank at the Magnolia Bend, interplanted with masses of pale blue Camassia leichtlini, is especially striking.
'Magnifica' frequently throws branch sports of clear lavender flowers which are extraordinarily fragrant. When he discovered that these remained true from cuttings, Mr. du Pont named the sport 'Winterthur' and propagated it extensively. On hot May days its scent is very refreshing. Two other lavender forms of mucronatum grow here: 'Lilacina' and 'Amethystina'. The latter has smaller, starrier flowers than the others and blooms earlier, which may point towards hybrid origin for it if not for the whole group. A final clone, 'Plenum' of 'Fujimanyo', is almost certainly a hybrid. It has rather small, very double mauve flowers and blooms early for a mucronatum form, on a dwarfer, less dense bush. Its narrow, sticky foliage may indicate hybridity with R. linearifolium. Mucronatum and its forms, whatever their status, provide some of the finest garden shrubs for our area. An added attribute of 'Magnifica' is that it blooms sporadically but quite effectively throughout the summer and autumn.
The latest species of the Obtusum Subseries to bloom in Delaware is the true R. indicum. We grow several forms here, all with double flowers except one. This last is the plant known for years in the trade as 'J. T. Lovett', which Wilson in his monograph on azaleas says is nothing but typical indicum. It is a low, dense, fully evergreen shrub with glossy, narrow leaves on strigose reddish branchlets. Its flowers are about 2½ inches across, a bright and rather deep pink, and appear in the middle of June. It is totally hardy here, and has been at Winterthur a very long time. R. indicum balsaminaeflorum is similar, perhaps even dwarfer in habit, with very double flowers of salmon red beginning in June and continuing sporadically throughout the summer. It has been growing here since at least the early 'thirties. 'Benikirishima' is similar but slightly deeper red in tone and more upright in habit. This was introduced by the USDA (PI771 13), I believe, after the war, and first came to Winterthur in 1949. Very similar is a clone called 'Mrs. C. C. Miller', which is attributed perhaps erroneously to Joe Gable. This came from Dr. Thomas Wheeldon of Richmond, Va., in the late 'fifties.
All these are invaluable for bloom during a period when gardens are comparatively bloomless. In effect they are quite different from the Kurumes, for their larger flowers open sporadically over a long period of time, rather than all at once. A rather too discriminating garden friend of mine once remarked that she could achieve the effect given by 'Hinodegiri' by spreading red tablecloths on her boxwoods, but was totally charmed by indica and its derivatives.
The logical plants to begin this discussion are the Kurume Azaleas, which in most of the East are as synonymous with azalea as Cattleya is with orchid. This group is remarkably uniform in everything but flower color: dense, compact, more or less evergreen, glossy-leaved shrubs which become smothered with inch-wide flowers in early May. The Kurumes at Winterthur are venerable plants, descendants of the first importations from Japan some sixty years ago. The bulk of them grows in the Azalea Woods, in great drifts of white, mauve, red (sparingly used) and many shades of pink. The names of most of these have been lost, though 'Apple Blossom', 'Cherry Blossom', and 'Pink Pearl', among the pinks, and the white 'Snow' retain their labels. The brilliant crimson 'Hinodegiri' also grows at Winterthur, but not in the Azalea Woods, for its color is irreconcilable with most others. It grows alone in a section of woodland beyond the Sundial Garden, surrounded by stretches of green lawn. Seen from a distance it seems a vivid streak across the landscape. 'Hinomayo', which is not one of the original fifty of Wilson but apparently a later clone of Dutch origin, does grow in the Azalea Woods. It is a pink of a particularly lovely shade.
A few color combinations utilizing these azaleas should be mentioned here. One occurs in the Azalea Woods, a large drift of a soft lavender Kurume backed by a few plants of the taller hybrid of amoenum x kaempferi called 'Arnoldianum' in garnet or cherry red. In juxtaposition the colors seem to change, the red seeming a purer red and the lavender almost a soft blue, very subtle and pleasing. Another combination, in a shady dell just beyond the Azalea Woods, utilizes lavender mauve Kurumes and Cutleaf and Persian Lilacs of more or less the same hue. The effect is to afford the eyes of the visitor rest after the riotous colors he has just passed through. Another combination, along an evergreen backed grass walk leading from the Peony Garden, uses the Kurume 'Coral Bells' (a hose-in-hose pink with rather pendant and tubular blossoms) with plants of Weigela florida venusta, an early-blooming weigela with flowers of similar shape and color, yet sufficiently different from the azalea to attract attention. Yet another group consists of white Kurumes beneath native dogwoods, in a wall of white paralleling a path from the Azalea Woods around the Pinetum and ending in a full vista of the March Walk and the Museum.
'Coral Bells' above the Peony Garden at Winterthur.
Among the old Kurumes are some particularly fine brilliant scarlet reds. Two of these, 'Yayegiri' and 'Firefly', grow on the green slopes of Oak Hill apart from others of their kind. The latter clone is one of the best of the Kurumes. It is a single (not a hose-in-hose variety as often listed) with glistening, intensely scarlet flowers. Mr. du Pont often described it in his gardening notes as "lacquer red". Its abundant, small leaves of glossy light green make it an effective landscape plant the year around. In some azalea manuals it is listed as a synonym of 'Hexe', but it is nothing like the cultivar of that name found in the trade today. At Winterthur 'Hexe' blooms later, with large, hose-in-hose flowers of a clear but soft crimson. It is obviously not of pure Kurume derivation; perhaps the southern indicas are involved in its parentage, for it is quite tender here, losing flower buds during all but the mildest winters. Our 'Firefly', on the other hand, is extremely hardy. A few other cultivars of similar scarlet coloration which belong to different groups but, like the Kurumes, bear rather small, early midseason flowers in great masses, are the Glenn Dale 'Trouper', the Gable 'Gable's Flame', and the Wheeldon clone 'H. F. du Pont'. These are planted together on the edge of the Azalea Woods. They are all excellent azaleas, as is an un-named clone growing with them called (or rather described as) 'Dark Mahogany', which came from Henry Hohman of Kingsville Nurseries in 1951. The Ouden azalea 'Addy Wery' is similar but unsatisfactorily tender to winter cold in Delaware, as is the well-known Kurume 'Ward's Ruby'.
Two aberrant Kurumes are the clones called 'Hatsushima' and 'Hooden'. These are large-flowered plants with variegated pink blossoms which are quite beautiful but rather tender in our winters. They are obviously not derivatives of obtusum.
There are several newer groups of mainly Kurume derivation which have been widely used at Winterthur. The Allan, Chisholm-Merritt, and YerkesPryor (Beltsville) Azaleas contain many clones which were favorites of H. F. du Pont's simply because there is an abundance of salmon-pinks among them. He was partial to pinks on the salmon or orange side in azaleas, and had an aversion to those with crimson or purple undertone ("blue-pinks," he called them), which are too harsh and arresting to use effectively in most landscape combinations.
In the Pinetum he planted a large bed of salmons beneath an old Styrax japonica, using 'Guy Yerkes', 'Colorado', 'Coral Cluster', 'Millicent', 'Flower Queen', 'Charlotte Weiss', 'Dessa Merritt', with the Glenn Dales 'Fashion', 'Favorite', 'Pirate', and 'Ambrosia'. All these are excellent clones, ranging in hue from soft coral pink to almost a salmon orange and combining beautifully with each other. 'Ambrosia' is perhaps the most interesting of these, almost pure apricot when fully open. Somewhat similar to these is the Kaempferi hybrid 'Henriette', a rather tall-growing salmon pink which inherits both vivid color and upright growth from the Torch Azalea. Its 21/2-inch flowers appear a little later than those of the Kurumes. This is a fine azalea, another favorite of H. F. du Pont's. The original plant came from Fred Street in England in 1947. It was heavily propagated and now dominates the southeast end of the Pinetum, coming into flower as the crab-apples there begin to fade.
As might be expected, the Gable Hybrids are widely used at Winterthur. These are a somewhat heterogeneous lot, with many species entering into their background. 'Viola' (poukhanense x mucronatum) is a good single lavender. Two large-flowered late purplish pinks of indicum breeding are 'Elizabeth Gable' and 'Louise Gable'. 'Mary Frances Hawkins' and 'Rosebud' are midseason salmon pinks, the latter very double. 'Carol' is a frilly hose-in-hose rose red with many blooms per cluster which blooms from mid-May to the first of June. Its color is reminiscent of that of the old-fashioned rambler rose, and fades paler as these old roses do. 'Rose Greeley' and 'White Star' are two fine early whites. The first azalea hybrid to flower in spring is the Gable clone 'Springtime', a cross of kaempferi and poukhanense. As might be expected from its parentage, this is a robust and very hardy hybrid which is partially deciduous. Its large, pink flowers on nearly leafless branches have a silvery sheen which makes them very beautiful in the early spring landscape. Joe Gable told me in the early 'sixties that the cross which produced 'Springtime' was the first he ever made and the best.
WINTERTHUR KAEMPFERI HYBRIDS
At Winterthur there grows a group of azaleas which I have seen nowhere else. H. F. du Pont called them "kaempferi hybrids," and stated that they were originally given to him by Prof. C. S. Sargent, whose gardener at Brookline, Mass., was an azalea hybridizer. These plants are quite uniform in appearance: tall, with stout, tree-like trunks and horizontally spreading branches (though one clone is much dwarfer than the others), with rather large flowers varying from salmon pink to red, most with a brick orange undertone, which appear after the Kurumes in mid - to late May. Like kaempferi, their flowers tend to bleach somewhat in full sun, and like kaempferi also they are extremely hardy - in fact they seed themselves in several locations. However, they bloom later than kaempferi, are more fully evergreen (though their large leaves quite resemble those of the Torch Azalea), and they have larger flowers with that strange brick-colored tint that so many indicum hybrids exhibit. They are, in other words, almost exactly intermediate between kaempferi and true indicum, and are probably primary hybrids of these two species.
Whatever their parentage, they are excellent ornamentals, big, showy old plants which line the walk that leads up the hill towards the Azalea Woods. Beneath them grow thousands of blue Scilla campanulata, and the combination lavender-blue and - what shall I call it, orange-rose-red? - never fails to enthrall our visitors.
Azalea Woods at Winterthur
In the late 'fifties an azalea came from Dr. Thomas Wheeldon, proprietor of Gladsgay Gardens in Richmond, Va., which soon became a favorite of Mr. du Pont's and one of the most widely planted at Winterthur. This is 'Miss Susie,' a reputed cross of simsii x mucronatum blooming in the early May with a ruffled 2½-inch flower of clear, luminous, luscious pink. Its foliage and habit are faultless and it has proved absolutely hardy here. 'Miss Susie' is planted with pink forms of the Korean Rhododendron (R. mucronulatum) and the Royal Azalea (R. schlippenbachii) among the great conifers in the Pineturn. The three provide a magnificent spectacle as they succeed each other in bloom, beginning with mucronulatum in early April and ending with 'Miss Susie' in the middle of May. As we all know, too many azalea cultivars of little distinction have been, and are still being, introduced. Here is a hybrid, though, which certainly merits wider use than it at present seems to get. I have only seen it at Winterthur
The Glenn Dale Azaleas deserve an article to themselves. There are literally hundreds of them, and, due to the wide array of species incorporated into their background, they exhibit little homogeneity as to type. Some resemble Kurumes, others clones of mucronatum or indicum, and still others exhibit all degrees of intermediacy between these types. I would say that too many have been introduced. For example, there are a great many mid-season to late bricky rose-reds which, though very attractive and very valuable in the garden, tend to duplicate each other's charms. Some of these are 'Beacon', 'Buccaneer', 'Copperman', 'Coquette', 'Coralie', 'Elizabeth', 'Glamour', 'Kathleen', and 'Picador'.
In a garden the size of Winterthur all can be planted together with marvelous effects. The average homeowner, however, would be hard pressed to select one or two of the best from them. I suppose my personal favorites are 'Beacon' for its depth of color, 'Copperman' for its tall growth and lateness, and 'Elizabeth' for its really enormous flowers.
Again, there is a group of derivatives of mucronatum with large mid-season flowers which are basically white with varying degrees of mauve or purple striping. Some of these are 'Dowager', 'Killarney', 'Sarabande', 'Memento', and 'Orison'. All are lovely, though similar to each other. At Winterthur they grow in combination with Fringetrees and Cotoneaster hupehensis. The off-white flowers of the latter two, plus the glaucous leaves of the cotoneaster, combine subtly and beautifully with the basically white but interestingly variegated flowers of the azaleas.
Another group of Glenn Dales combines the adaptable mucronatum with the large-flowered Satsuki. These are fairly robust shrubs with hairy leaves and large, late, often variegated flowers. They are a shade more tender than most of the others, but satisfactory in Delaware. 'Helen Gunning' is a beautiful big pink with darker blotch. 'Martha Hitchcock' has an enormous flower like a big white bowl with a pale purple rim. There is nothing quite like it.
Three clones are pure (or nearly pure) indicum, with the compact growth, glossy foliage, and late flowers of that species. These are 'Sterling', 'Stunner' and 'Sagittarius', June-blooming pinks and really fine azaleas.
Since we grow about sixty cultivars of Glenn Dales, space does not permit analyzing the good and bad points of them all. Some of the best of those unmentioned so far, however, are 'Dayspring', an early two-toned pink, one of the first azaleas to bloom; 'Glacier', a fairly late white with large flowers and perhaps the best (because extremely bright green and glossy) foliage in the subseries; 'Trouper', an excellent scarlet of Kurume type; 'Delos', a tall, upright midseason with double pink flowers that are pendant like fuchsia blooms; 'Dimity', early and rather small-flowered, with interestingly variegated blooms, pink on pink; and 'Wavelet', a mucronatum x Satsuki cross with enormous yellow-blotched white flowers at the end of May. 'Treasure', another white clone, is widely used here. It was distributed as a replacement for the old "Ledifolia alba," but in my judgment is not as good, for its color is flawed by a sort of brownish pink undertone.
The last hybrid group to flower (beginning in June) at Winterthur is the Satsukis, which according to Frederick Lee are derived from indicum and its form eriocarpum with an admixture of blood from the Belgian Indica Azaleas. We have grown perhaps thirty-five clones at Winterthur, though not all have survived. The Belgian Indica blood in some, notably the magnificent 'Shinnyo-no-Tsuki', renders them unsuitable for our climate, and all are quite tender when young, though mature plants seem fully hardy. As we grow them, the Satsukis fall roughly into two types: the "Gumpos," very dwarf plants with often frilly, large flowers (though very large for the size of the plant), and the Howraku-type, somewhat taller, with quite large to enormous flowers which are commonly white and striped, zoned, rayed, or margined with pink or purple. Of the first type (which is probably almost pure eriocarpum) the best are perhaps "Gumpo', 'Gunbi', and 'Bunkwa' - white, pink-blotched white, and soft salmon respectively. These have grown here for over twenty years; in fact, our records show that a plant of 'Gunbi' was purchased in 1942, only a few years after the Chugai nursery of Japan sent out its first exports of this group. In the second group, 'Howraku' is probably the showiest, and a showy thing it is, with a four-inch bloom of white, rose-pink, or combination of the two. This clone has grown at Winterthur since 1949, and has reached nearly four feet in height. Several others are similar to 'Howraku', though most don't quite equal it in flower size. Quite different and quite showy is 'Tamasugata', with pale pink, red-bordered flowers more than three inches wide. This clone has also grown here since 1949. Another showy cultivar is 'Shun-pow', whose large flowers vary from white to pure, vibrant, deep purple.
Because their flowers are so large and bright - almost garish - in color, these azaleas are nearly as difficult to use in the natural landscape as hybrid petunias. H. F. du Pont planted them on a steep bank overlooking the Quarry, so that the visitor, as he walks the path below the bank, looks up at them and sees them backed by a white structure called the Bristol Summerhouse at the crest of the hill. Later, after he has followed the walk circling the Quarry, he comes upon a sudden break in the wall of forest trees which gives him a view back across the Quarry towards the hillside, which is capped by the little white summerhouse and studded with mounds of colorful azaleas, all framed by green boughs of beech and hemlock. It is a perfectly charming picture, contrived enough to look like something you'd see hanging on the wall of an English country house, yet not too cloying (or "gardenesque," to use H. F. du Pont's pejorative term), and in my opinion one of the most effective views in the whole garden. I suspect that Mr. du Pont felt this way, too, for he had a sign driven into the ground at this point which succinctly states: "Keep this view open forever."
There remain to be mentioned those azaleas which have failed at Winterthur. Some I have discussed in passing. Others, like the Southern and Belgian Indicas have proved entirely tender. A group called Gold Cup of California Hybrids, which is probably derived from the foregoing, has proved tender also, with the exception of a clone called 'Sun Valley' which is an excellent, large-flowered white. The Pericats, again descended largely from the tender Indicas, are really lovely in flower but impossible for us, with the exception of 'Pericat Orchid', unfortunately the least attractive of the group.
Perhaps it is fitting to end this article with a list of those cultivars mentioned most frequently by H. F. du Pont in his notes and directives on propagating, planting, and purchasing - those that he liked so much that he wanted more of them: in a word, his favorites. These are 'Hinomayo', 'Firefly', 'Henriette', 'Miss Susie', 'Ambrosia', 'Guy Yerkes', 'Flower Queen', kaempferi, 'Magnifica', 'Gumpo', 'Gunbi', 'Sagittarius', and 'J. T. Lovett'.