JARS v45n1 - Rhododendrons at Bear Swamp Gardens

Rhododendrons at Bear Swamp Gardens
Elinor Clarke
Ashfield, Massachusetts

Reprinted from "The Rosebay," a publication of the Massachusetts Chapter.

Growing Conditions
We started growing rhododendrons here at Bear Swamp Gardens in Ashfield, Massachusetts, in 1969 when David Leach (at that time a total stranger) sent me a rooted cutting of his Rhododendron 'Mist Maiden'. I did not know enough to protect its three tiny branches from the weight of snow, so it did not survive the first winter here.
Everything I have done with rhododendrons since then, including founding the Massachusetts Chapter of the American Rhododendron Society, can be credited to that single act. Without it I would not have known Jon Valigorsky and this article would not have been written. I thank both David and Jon for all their help over the years and now in getting this evaluation together. I also thank Dean Barber, Cliff Desch, Fred Serbin and John Smart.
Since 1969 a tremendous number of rhododendrons have been added to the Bear Swamp Gardens landscape. About fourteen of 187 acres are devoted to them, scattered over quite a wide area.
Each time I find a new planting site that they might tolerate particularly well, scouts are sent out the first year and presently an entire platoon is standing waiting for attention. Many soldiers have fallen by the wayside over the last twenty years. This inexperienced general ought not to have ordered them to do battle against such odds!
Elevations at Bear Swamp Gardens run from 1,680 feet (512 meters) to 1,760 feet (536 meters) above sea level, probably the coldest site in the Northeast where large numbers of rhododendrons are grown. The average winter low temperature is -20° Fahrenheit (-29° Celsius), while the maximum winter low temperature is -25° Fahrenheit (-32° Celsius).
Planting sites vary considerably with their exposures. One soon learns which locations are the most benign - those with enough light but a minimal amount of wind, particularly in winter. Light can be increased by cutting down trees and soil can be amended in several ways, but it is much more difficult to avoid strong winds.
When working with rhododendrons of dubious hardiness, one soon learns to start young plants in the most benign areas, moving them on as their wood matures. Often the original growth of west coast plants will die right to the ground, but this does not worry me if first they have sent out a rosette of young leaves at the base.
Rhododendron 'Taurus,' R. 'Grace Seabrook,' R. ' Sweet Sixteen,' and R. Virginia Richards' are among those with which I am gambling now. They are already surviving without winter rose cones, which, when used, have the Styrofoam tops cut out for ventilation and to permit moisture entry.
Of particular concern are normally quite satisfactory planting areas that hold too much water in the ground during an excessively wet season, such as spring 1989. Nearly twenty years ago, I had several plants of R. 'Goldsworth Yellow' that were found in standing water when the snow melted.
Dick Leonard in Raynham, Massachusetts, had a similar experience that season. We waited for them to die, as they were supposed to after 48 hours in standing water. All of our plants survived. We attributed this to the low temperature of the water, and moved them to higher ground as soon as we could.
After this experience, I learned to look for even a slight change in grade. If this is absolutely not convenient, I set the plants a bit higher than usual and make up the difference with loose mulch.
In the heavy soil of Bear Swamp Gardens we mix bark mulch and peat moss with the soil in the planting holes, adding a handful of nitrogenous fertilizer for the bark mulch as it breaks down. We never set rhododendrons in the saucers so dear to the hearts of many people who find out too late that the ice which formed in the saucers split the bark and killed their plants.

Weather the Year Before Evaluation
On May 20, 1989, Jon Valigorsky and I spent an afternoon walking around these gardens looking for the elepidote rhododendrons that had best survived the winter. At first we set a selection of ten as our goal, but soon decided to change that to twenty-five. Even so, we had difficulty keeping to the twenty-five.
The stage had been set for a worse than usual winter on December 12, 1988, when the temperature dropped to -16°F (-27°C). In a typical year, the lowest temperatures do not occur until mid-January. No snow cover made conditions worse that December.
Spring was late here in 1989, so on May 20th we were catching these plants at a moment of truth, before the buds had begun to swell. They were still much as they were at the end of winter.
As spring went on, totally dead-seeming branches sprang to life. In general, the bloom was better than ever before - no doubt because of the prolonged dry spell during the summer of 1988, with the resulting overall heavier bud set.

Observations About R. catawbiense , R. ponticum and R. fortunei Heritage
We soon realized that the Ironclads had suffered the most. One quarter of an old R. 'Roseum Pink' had been completely killed, and other plants appeared more or less moribund. Some eventually resurrected, even blooming without leaves. We would NOT rate R. ' Roseum Pink' hardy to -25°F (-32°C).
I had always thought the worst count against R. catawbiense was the blue admixture in the flowers of its progeny, but had assumed that it nevertheless conferred hardiness. Rhododendron ponticum of southwestern Europe and Asia Minor, a species that does well in the British Isles, is in the same taxonomic group as R. catawbiense , i.e., subgenus Hymenanthes , section Hymenanthes , subsection Pontica . It seems that the R. ponticum in some Ironclads makes them less hardy.
This lack of hardiness is, of course, an even more serious count against R. ponticum . Our observations on May 20th have stimulated Jon and me to further investigation into the effect on hybrid rhododendrons of having species R. catawbiense and R. ponticum in their heritage.
The surprising thing was what we observed about R. fortunei inheritance. All the plants with R. fortunei blood generally had superior foliage hardiness and tolerated the snowless winter noticeably better than the Ironclads.
For years I have grown and regularly flowered two plants given me as R. fortunei . They are among my biggest favorites. I have never seen any winter burn on them and cannot recall any blasted flower buds. One thing that came out in the wash was that apparently neither of these are true R. fortunei .
Several years ago, Jon and I purchased at a Connecticut Chapter, ARS, auction a plant of the Lushan form of R. fortunei . This plant has the distinguishing scarlet leaf bracts as described by David Leach. Characteristic, too, of the true species are leaf petioles of purplish, bluish or reddish color. Jon says the Lushan form blooms well for him in Pittsfield, Massachusetts, after -12°F (-24°C), that it branches well, and is insect resistant.
My two large plants of an R. fortunei hybrid do not have the scarlet leaf bracts of the Lushan form but are otherwise the same: the same glossy blue-green, somewhat pointed leaves and the same ease of propagation, although reputed otherwise.
The sources of my two R. fortunei plants of unknown parentage are: (1) Bill Thompson via John Smart, and (2) Al Pressy via Dean Barber. Al Pressy of Manchester, New Hampshire, had gotten his plant from Joe Gable. I understand that Gable grew his R. fortunei from seed rather than cuttings, so the plants are seedlings rather than a distinct named form of the species. Jon gave me a cutting propagated plant of the Lushan form, now about four feet high with striking foliage.
In any case, I shall now pay particular attention to R. fortunei , singling out for closer observation all the hybrids that we have here with R. fortunei in their ancestry. It is evidently a hardier species than generally supposed, as David Leach has noted and Dexter and Consolini proved. I understand also that the hardiness of this species is quite variable, so I may have a lot to learn.

The 25 Best Survivors of the Winter of 1988-89
You will recognize Dexter and Leach hybrids on this list, all of which are so well known, with information about them so readily available, that I shall not go over them minutely, but just make a few comments. In the table, I have indicated with a "C" and an "F" those plants containing R. catawbiense and/or R. fortunei in their background.

Bear Swamp Gardens 25 Best Rhododendrons After Winter of 1988/89
Cultivar Hardiness Parentage Best 10
'Anna H. Hall' -25F / -32C C *
'Besse Howells' -20F / -29C C
'Ben Mosley' -17F / -27C (JV) F
'Blue Peter' -15F / -26C ?
bureavii Flink form *
'Canary Islands' -20F / -29C C F?
'Champagne' -15F / -26C F
fortunei X -12F / -24C (JV) F *
'Francesca' -20F / -29C (JV) C F
'Gloxineum' -17F / -27C (JV) F
'Gretchen' -15F / -26C C F
'Harold Amateis' -20F / -29C
'Henry's Red' -25F / -32C C *
'Janet Blair' -17F / -27C (JV) F *
'Ken Janeck' -20F / -29C (EC)
'Mist Maiden' -20F / -29C
'Normandy' -20F / -29C C? *
'Parker's Pink' -17F / -27C (JV)
'Pearce's American Beauty' -20F / -29C F *
'Pink Cameo' -20F / -29C C
'Pink Parasol' -20F / -29C
'Swansdown' -25F / -32C C
'White Swan' -15F / -26C (EC) C *
'Wyandanch Pink' -25F / -32C (JV) *
'Years of Peace' -20F / -29C (JV) F
(JV) = Jon Valigorsky Assessment
(EC) = Elinor Clarke Assessment
C = R. catawbiense in parentage
F = R. fortunei in parentage
? = Questionable

Rhododendron 'Anna H. Hall' I consider one of the hybrids of the century. Each year it sets buds on nearly every terminus, almost none of which ever blast. The texture of the flowers, as well as the clean pink and white, remind one of organdy. Here it is one of the earliest elepidotes to bloom. It can take quite a bit of sun, but young or recently acquired plants should have some wind protection. For twenty winters it has bounced back better than ever each spring.

Rhododendron 'Ben Mosley' is one of the plants I purchased from Warren Baldsiefen two decades ago. It is among our very best, rated bud hardy to -17°F (-27°C) by Jon. The foliage is glossy and the wine red throat carries well, an advantage since most of our rhododendrons are seen from a distance. Rhododendron 'Ballad,' with smaller flowers, also carries well. Dean Barber has been quite pleased with R. 'Ballad' at Contoocook, New Hampshire. Unfortunately, neither has the fragrance of R. fortunei.

Rhododendron 'Besse Howells' is my favorite Shammarello hybrid. Some folks complain because it is not fire-engine red, but I wish you could have seen it under-planted with forget-me-nots in a Montreal garden. The frilled old-rose flowers have a unique charm. Rhododendron 'Besse Howells' blooms here regularly. We heartily agree with the published hardiness rating of -25°F (-32°C).

Rhododendron 'Blue Peter' flowers here in a variety of locations, in spite of the possible R. ponticum in it. This is another cultivar with a blotch and distinctive leaves. Jon has found it very susceptible to black vine weevils.

The Flink form of R. bureavii is easily one of our best foliage rhododendrons, although the now large plant has yet to set flower buds. My plant had been donated to a Connecticut Chapter, ARS, auction by Dr. Fred Serbin. It had been given to him by a Mr. Flink, a friend of King Gustav of Sweden, where it grew in his garden. It was labeled R. bureavioides , but that name is no longer valid so it has been relabeled R. bureavii , Flink form. This form grows to about nine feet at maturity, about twice as tall as the rest of the species. It did not take long for me to decide to grow this plant for foliage alone. The leaves are unusually glossy on top, dark green and of heavy substance. New growth indumentum is white, mature indumentum is tan. Branching is excellent.

Rhododendron 'Canary Islands' is the youngest plant in this group of best survivors, too young to have set flower buds. Jon Valigorsky noted that if we had been talking about his garden instead of mine, he would have listed R. 'Golden Gala,' but my plant of R. 'Golden Gala' is still quite small, although it bloomed after the winter of 1988-89. The perkiness of R. 'Canary Islands' impressed me. Jon commented that these yellows can be made to appear more yellow by planting them next to pure whites.

Rhododendron 'Champagne' is one of our favorites. It has been utterly reliable here for twenty years. The bloom is stupendous every season, the fragrance astonishing to those who do not associate fragrance with rhododendrons. The olive foliage is distinguishing. It also buds while quite young.

Rhododendron fortunei hybrids: See preliminary comments.

Rhododendron 'Francesca' has flowered well here every year, but we have been told of places where it has not survived. This could be accounted for by the R. griffithianum in its parentage, a very complex one containing both R. catawbiense and R. fortunei . Jon remarked that R. 'Francesca' ought to have some shade to preserve the color. We are growing it in the open in a north-facing area.

R. 'Francesca'
Photo by Jon Valigorsky

Rhododendron 'Gloxineum' also has been fully dependable over two decades. Jon has used it in breeding. I have a substantial plant of his cross of R. 'Gloxineum' with R. 'Catalgla' and am looking forward to it setting flower buds. It looks already as though it is going to require as much space as R. 'Gloxineum' itself. Branches of R. 'Gloxineum' are thick like those of R. 'Scintillation,' which we almost included, but plants of R. 'Scintillation' here in the open had suffered, so we did not list it.

Rhododendron 'Gretchen' is so similar to R. 'Rochelle' that first we put R. 'Rochelle' on the list. Their parentage is almost identical, but R. 'Gretchen' has a greater air of distinction. It is flower bud hardy to at least -15°F (-26°C), with good branching, foliage like R. decorum , which you may recall is in subsection Fortunea.

Rhododendron 'Harold Amateis' was priced by Warren Baldsiefen at double the rest of his rhododendrons. The plant I purchased from him took 14 years to bloom. The flowers are not a bad red but I grow it for the foliage. It is remarkable that the leaves of an R. strigillosum hybrid have never shown any browning here. Once R. 'Harold Amateis' finally started blooming, it continued to do so. Cuttings root readily. It was not yet in bloom on this May 20th, but not much else was either, as spring was unusually late. Anyway, we were not looking for bloom but at the condition of the plants. Rhododendron 'Harold Amateis' is a collector's plant. I have never recommended it to a client. One has to have quite a large garden to contribute space to non-bloomers.

R. 'Harold Amateis'
'Harold Amateis'
Photo by Jon Valigorsky

Rhododendron 'Henry's Red' is the best red we flower. Like R. 'Francesca', the color lasts longer in light shade. Rhododendron 'Henry's Red' is certainly superior to R. 'Nova Zembla', the leaves of which were almost totally burned last winter. In addition, the red of R. 'Nova Zembla' contains too much blue and it is said to be more than normally susceptible to Phytophthora. The best red is reportedly R. 'Snow's Red', but my small plants have not bloomed yet.

Rhododendron 'Janet Blair' is another plant of the century. It may well be somewhat hardier than the rated -15F (-26C). In the last two decades it has never failed to bloom extravagantly. One mature plant, set low at the entrance to a ravine, was spectacular last spring. It was covered with flower buds on May 20th, all of which opened eventually. Since I had planted it in a natural venturi as an experiment, I have been astounded by how well it has performed. If it likes ventilation, it is getting it here! I frequently take chances when I have a number of identical plants, as that is how we learn. Incidentally, the plants that came to us as R. 'John Wister' are not identical to R. 'Janet Blair' as they are supposed to be. This is one more puzzle I have not solved.

Rhododendron 'Ken Janeck' blooms well here every year. If I had to choose among R. 'Mist Maiden', 'Pink Parasol' and 'Ken Janeck', it would be R. 'Ken Janeck' because it is flower bud hardy to at least -25°F (-32C) - quite possibly hardier than the other two. Also, the individual flowers are larger, in spectacular trusses, the leaves broader and flatter. The plant habit is as dense as any species R. yakushimanum , of which it is supposed to be a selection, not a hybrid. (For a discussion of species vs. hybrid, see M.J. Harvey, "The Nature of Rhododendron yakushimanum Clones," p. 202, and David G. Leach, "The Nature of Evidence for Hybridity in Rhododendron yakushimanum 'Mist Maiden', 'Pink Parasol' and 'Ken Janeck'," p.207, ARS Journal ,Vol.42:4, Fall 1988.)

R. 'Ken Janeck'
'Ken Janeck'
Photo by Jon Valigorsky

Rhododendron 'Mist Maiden' is another of our Baldsiefen plants. First they were planted in too much shade, both here and at the Display Garden in Stanley Park, Springfield, Massachusetts. We had made the mistake of treating it as an ordinary elepidote. All of those plants had to be moved out into more light and better ventilation. When one thinks of it, the only sensible thing is to try to reproduce the conditions under which a species grows naturally in the wild. For instance, it has taken an indumented species, such as R. bureavii , R. smirnowii or R. yakushimanum some millennia to adapt to stringent conditions, and this is not going to be reversed during a lifetime in your garden or mine.

Rhododendron 'Normandy' bids fair to become known as one of the very best. Not only does it flower early in life but also very heavily, at least in alternate years. This spring the bloom lasted a full two weeks with no sign of wilting. The substance of the flowers is above average. The -20°F (-29°C) hardiness is a characteristic of both its parents, R. 'Newburyport Beauty' and R. ' Newburyport Belle.' Dexter hybrids have suffered from the reputation of being on the tender side. My experience with them and with their further hybrids certainly belies this. (See Jon Valigorsky, "Hardy Dexter Rhododendrons," p. 206, ARS Journal , Vol. 43:4, Fall 1989.)

Rhododendron 'Parker's Pink' we have had also for many years. Jon reports it bud hardy to at least -17°F (-27°C). Both of us have found it floriferous, even in moderate shade. Although reputedly hard to root, I have had good luck with rooting cuttings.

Rhododendron 'Pearce's American Beauty' is a great favorite for glowing color and for the size and shape of trusses. The R. arboreum in it may account not only for the vivid color but also for the low hardiness ratings. I have seen it rated at 0°F (-18°C), elsewhere at -15°F (-26°C). We have found the latter published rating much more accurate, and it may be hardier still. Rhododendron catawbiense , as usual, contributed its share of blue to the flowers, but because of the sheen, it does not seem objectionable. One wishes hybridizers could breed for this particular glowing color quality. I hope for that and pliability.

Rhododendron 'Pink Cameo' is another old Shammarello hybrid. It is all the more interesting to me because we grow the R. catawbiense form rubrum used in the original cross, a plant that makes one realize the difficulties of the early hybridizers in finding suitable parents. Remarkably, the seed parent of R. 'Pink Cameo', R. 'Boule de Neige', did not in this instance contribute the R. catawbiense propensity to winter-burn damage of the leaves. Last winter, every plant we had of R. 'Boule de Neige', in all exposures, burned badly. There were better whites to use in the landscape than R. 'Boule de Neige', such as R. 'White Swan' and R. 'Swansdown'.

Rhododendron 'Pink Parasol' a close runner-up to R. 'Mist Maiden', holds its pinker color longer than most R. yakushimanum selections. We had to move this plant to more light for it to set flower buds, which it promptly did.

Rhododendron 'Swansdown' first took my eye years ago at the Pittsburgh ARS convention. Although the flowers are similar to those of R. 'Lodestar', which we also grow, the foliage is a darker green and the plant has more style.

R. 'Swansdown'
Photo by Jon Valigorsky

Rhododendron 'White Swan' is one of my favorites, particularly for the red resting winter buds. If severe frost is delayed, the red buds may be enjoyed for quite a while. Eventually they turn brown but do not blast. We take great exception to the -5°F (-20°C) hardiness rating of this old British hybrid (Waterer, Sons & Crisp). It is bud hardy here to at least -20°F (-29°C) and may be hardier. This is noteworthy, considering the R. decorum , R. griffithianum and R. arboreum in its lineage. A trip through the ancestries in Salley & Greer, Rhododendron Hybrids , is always illuminating.

Rhododendron 'Wyandanch Pink' is a superb plant. It actually prefers full sun. While it does not bloom early in life, once it starts, it flowers prodigally. It is a hybrid not listed in Salley and Greer.

Rhododendron 'Years of Peace' is R. 'Mrs. C.S. Sargent' selfed, one more outstanding result of selfing an already fine hybrid. (You may recall that R. Trude Webster' is R. 'Countess of Derby' selfed. Unfortunately, all attempts to grow R. 'Trude Webster' here, along with R. 'Loderi King George', have failed.)

All these years I have hesitated to make any evaluation of my plants because I felt that I could not be sufficiently definitive - and I still cannot. This evaluation was made on a particular date after a very unusual winter and of a finite variety of plants, not all of which had bloomed here, but most had. Those that were budded May 20th 1989 did bloom subsequently.
Since we made this selection, I have wondered why we did not include R. 'Catalgla', R. 'Goldfort', R. 'Apple Blossom' and a number of others. Even R. 'Dexter's Spice' has bloomed here, but sparsely so far. Cliff Desch in Conway, Massachusetts, would have included his R. 'Scintillation', and I would have included a R. 'Scintillation' on the Smith College campus, but we were dealing with plants at Bear Swamp Gardens in Ashfield, Massachusetts.
One may deplore the "one in ten" winters, but there is no better learning experience. With the amount of snow protection we normally get in this cloud belt, we are tempted to false assumptions as to flower bud and plant hardiness. A winter like that of 1988-89 sets the record straight.
The bud set in summer 1988 was better than usual due to a prolonged dry spell. Two weeks was the longest dry period we had in summer 1989. Although good, flower bud set for spring 1990 is not what it was the previous year. Jon Valigorsky reports the same.
The list of "25 Best Survivors" may be quite different after another five or ten years, as we have a great many more rhododendrons, mostly hybrids, under observation. At least local garden centers are offering a greater selection of rhododendrons than they did twenty years ago, perhaps due in part to the efforts of the Massachusetts Chapter, ARS.

Elinor Clarke was "the driving force most responsible for the formation of the Massachusetts Chapter" on October 3, 1970, to quote from the citation accompanying the Bronze medal she was awarded by the Chapter in 1974.