Rhododendrons In Our Eastern States - Can The Blooming Season Be Extended By April And June Bloom?
John C. Wister, Swarthmore, Pa.
Fig. 41. Hardy rhododendrons in the Dexter Garden on the East Coast.
Dexter Estate photo
In the Philadelphia and New York City areas, our best rhododendrons bloom from mid-May to June first or even through the first week in June. We do have R. mucronulatum, and a few of its varieties and hybrids, in late March and early April, and we do have R. maximum in late June and early July. But by and large most Rhododendron growers concentrate on the last two weeks in May.
In the milder climate of the West Coast, by contrast, there are important rhododendron species and hybrids in February, March and April to a peak in early May, and then continued bloom into midsummer.
What can East Coast rhododendron growers, with their more severe climate, do to extend their season, by producing more and finer April blooming varieties, and many more and much finer kinds that bloom from mid June into mid-July or later?
As a preface to some remarks on this general subject I should like to call attention to the remarkable work of the Iris Society, the Peony Society and the Hemerocallis Society. In the past decade, particularly, they have encouraged Iris, Peony and Hemerocallis breeders to produce flowers not merely of larger size, finer form, better substance and greater range of color, but of a much longer season of bloom.
Like the American Rhododendron Society, these three societies are composed of amateurs, commercial growers, breeders and plant scientists; they have volunteer (unpaid) officers and committee members; they hold yearly conventions and shows. What they have accomplished can be a guide, and should be an inspiration to us.
The varieties of these three flowers that are seen by the greatest number of members are those that bloom when the national conventions and shows of these societies are held. For years, therefore, these were the varieties most in demand and the most profitable for breeders to produce and for nurserymen to propagate and sell. And for years the greatest improvement in Iris was in the Tall Bearded varieties that bloom in New York from May 25 to June 1; in Peonies in the double Chinese varieties that bloom in mid-June; and in hemerocallis in the varieties which bloom in mid-July.
This has been true throughout most of the period of the greatest development of these three flowers, but since the 1930's a gradual change in the tastes of the members of these societies has been taking place. The change was unnoticed at first, but since the early 1950's has become most important.
In hemerocallis we are now getting varieties that bloom through August and into September and even October. In Peonies there has been the extraordinary development of early hybrids that bloom from two to four weeks before the Chinese Peony. Within the Iris Society there have been formed smaller special societies devoted to April and early May blooming varieties, to dwarf or miniature table Iris, and to mid-June and July blooming Spurias, "Louisiana" hybrids, and Japanese kaempferis. The growers of Iris, Peonies and hemerocallis can now enjoy their flowers for many weeks and sometimes for many months longer.
What about the eastern members of the American Rhododendron Society? Are they going to become more interested in earlier blooming and in later blooming rhododendron varieties?
I hope so, though I don't expect this to happen over night. It will take some time before enough members want these to make it worth while for breeders to see what they can produce. Let us take a look at what might be done.
For late March and April bloom we have R. mucronulatum. We shall hardly find anything that blooms any earlier. We hardly want anything earlier on account of the danger of spring frosts. But most of the plants of mucronulatum now available have been grown from seed and are predominantly magenta. This is a color many of us don't like too much, and a difficult color to harmonize with garden flowers. We do have varieties with other colors but they are not yet widely known or generally available. The oldest of these 'Cornell Pink' was selected from a large batch of seedlings by Henry Skinner years ago when he was at Cornell. It and other pink forms being selected by Joseph Gable, by Warren Baldsiefen and by Paul Vossberg point the way to future interbreeding and to crossing with selected white and peach pink forms of R. carolinianum and other lepidotes. We already have Gable's 'Conemaugh', R. 'Conestoga', and R. 'Conewago' which we value, but, like R. mucronulatum, these are too magenta for some tastes.
I do not know enough about other early species or types or hybrids to venture further remarks on this part of the subject here. In any case it is enough for a start.
Now what about late varieties? Whenever development of these is suggested someone suggests R. maximum and someone, often an experienced breeder, also immediately suggest it will not produce anything worthwhile.
I am not a breeder and not experienced and, therefore, I gladly stick my neck out and say, "I don't believe it." Then when I am pressed for a reason I hedge a little and fall back on the plea that I don't believe enough breeders have tried it enough times in enough years with enough different species and varieties to prove anything. I want, in other words, to see a lot of people try it with the hope that someday someone will come up with something. Judging by long failures and then ultimate success in other genera, I don't believe that is an unreasonable hope.
Dr. Earl B. White, a Washington member of the American Peony Society, made over 500 crosses with pollen of Paeonia mlokosewitschi on varieties of Chinese peonies before he got a single seed on the variety of 'M. Jules Elie.' That seed produced the famous yellow Peony 'Claire de Lune'.
Dr. A. B. Stout made over 5,000 crosses on a special wild form of Hemerocallis fulva at the New York Botanical Garden before he got the first seeds. The resulting plants produced flowers that weren't too good but they later became the parents of his finest varieties.
More than thirty years ago Guy Nearing secured pollen of a form of R. discolor growing at Longwood and crossed it on R. maximum. We have at Swarthmore two of the resulting plants. The flowers are not in a class with R. 'Mrs. Furnival' or even of R. 'Mrs. C. S. Sargent', but they come at Commencement time (usually between June 4 and 12) when all other rhododendrons are over. They are particularly valuable to us for this reason. They should, in my opinion, be more widely tested.
At the International Rhododendron Conference, Portland, Oregon, Dr. Clement Bowers told of crosses he had made on R. maximum some thirty years ago. He was disappointed in the results. I have seen a few of the plants now grown at "Planting Fields" on Long Island. I agree that they do not compare favorably with the modern British varieties or even with the best of our "Ironclads." But I wish that they might be tested to see how they behave in such differing climates as Boston, Philadelphia, Washington, Brookville and Cleveland. If in any one of those localities they did seem valuable in giving some late bloom, then I think they might be commercially propagated for these localities if and provided any nursery man would be willing to take a chance on them.
I am fully aware of the opinion of nurserymen that any rhododendron which is not in bloom on a handsome young plant the last two weeks in May, when the general public is buying at roadside garden centers, has two strikes on it. I do hope, however, that in due time through the efforts of our Society enthusiasts a market will develop for very early and very late varieties.
But let us suppose not a single one of Dr. Bowers' late flowering seedlings proves to be good enough to be named and introduced. Should they then be thrown away?
I do not think so. They have one very valuable trait. In a locality where all the Ironclads are through blooming the first or at most the second week in June, these seedlings begin to bloom after June 15. Some of them are at their best about June 20, others about June 25. There are others even later, opening the first week in July.
Is not that late blooming trait important in giving us a longer rhododendron season? Can not enthusiastic (and young) amateur breeders be found to use these seedlings for crossing? They should be intercrossed. They should be crossed back on R. maximum and R. discolor. They should be crossed on other late species and late varieties for late flowers, and on earlier blooming species or on Ironclads and on the finest modern British varieties for more color or better flowers.
Can the American Rhododendron Society encourage such breeding?