For The East Coast A Few Early Flowering
And Late Flowering Rhododendrons
Dr. John C. Wister, Swarthmore, Pa.
The general run of gardeners, along our east coast from Boston to Washington and inland for a hundred miles or so, have long recognized the beauty of Rhododendrons, and have planted what species and varieties have been generally available in nurseries near them. These are usually half a dozen or a dozen varieties of "Ironclads" that will bloom in late May or early June, and the species Rhododendron maximum that will follow in late June. By sticking to these few items they miss the opportunity of having the really long season they could enjoy by adding the less well known April and early May blooming species and varieties, as well as kinds that fill the gap between the "Ironclads" and R. maximum.
We, in the east, of course, cannot have the long season enjoyed by our friends on the Pacific Coast, but where I live in southeastern Pennsylvania we can have continuous bloom from early April until the end of June. R. mucronulatum is a most valuable shrub, coming into bloom about the first of April with the Forsythias. Plenty of people do not admire the magenta flowers, but if it is planted with plenty of green around it or against a white building it can be truly magnificent. Like any other early flowering plant it may, of course, be injured by a late frost, but in the twenty years or more that I have grown it that has never happened to the plants that I have known, though various neighbors have told me they have lost flowers. In any case it is the first early kind I can recommend. Anything coming much before that certainly would be subject to much more frost damage.
For those who do not like the color of mucronulatum there are now available beautiful pinks. The best known of these is 'Cornell Pink', which comes a few days later than the type. I do not know just how big this will grow in time. From the plants I have grown or seen elsewhere, it seems to be more compact than the type. We have here at Swarthmore also, a pink strain offered by the Westbury Rose Nurseries and one offered by Warren Baldsiefen. We like them both. The colors are enough different from 'Cornell Pink' to make a pleasant addition.
I have been interested these past few years in new selections or hybrids of Joseph Casadevall of Whippany, New Jersey. He has a group of 20 or 30 seedlings that cover quite a range from white or almost white, through the palest pinks to rose pink and to deeper colors than 'Cornell Pink.' These are not yet in commercial production. 1 hope that from the many I have seen, Mr. Casadevall will select a few to name and have them propagated so that they may be available.
There are two other quite widely grown early flowering kinds. The first one, 'Praecox', is a hybrid of ciliatum x dauricum. It was raised about 1860 by Davis in England, and apparently should be considered as a strain or "grex" rather than a clone. The flowers are purple to rosy lilac and come early in April. This also is a difficult color to use, but if properly surrounded by green foliage can be very effective. The other, 'Rosamundi', is a caucasicum hybrid of the grand old British firm of Standish and Noble. All the plants I have seen are rather low growing and compact, and the flowers are a good pink and beautifully frilled.
I have seen at Winterthur 'Nobleanum', a caucasicum x arboreum hybrid dating back to 1835 and R. praevernum, a species of the Fortunei Series. Both of these bloom in March. I think, for most gardeners, they are not worth attempting as they are apt to be hurt so often.
I have not seen 'Jacksoni' a hybrid of caucasicum and 'Nobleanum' raised by Herbert way back in 1835 but Joseph Gable has raised seedlings of it and selected one of a beautiful pink color. This he has identified merely as 'Jackson # 5'. It has bloomed for us between the 22nd and 25th of April these past few years, has very lovely rosy pink flowers with deeper stripes on the outside of the petals. It is decidedly worthwhile to carry along the Rhododendron season. I do not know how widely it has been distributed by Mr. Gable, but from what I have seen of it so far, it certainly deserves wide planting.
There are various other hybrids to be considered. Mr. Gable years ago made crosses between R. mucronulatum and various other lepidote species. Among those that he sent out about 1934 were 'Conemaugh', (racemosum x mucronulatum), 'Conewago', (carolinianum x mucronulatum) and 'Conestoga', (carolinianum x racemosum). The first generation seedlings of these crosses all have pinkish lilac to magenta flowers and for this reason have not been admired as much as I think they deserve. The second generation seedlings now coming along under the same names are producing some beautiful clear pinks and plants of these colors should be selected for the future.
Smaller growing plants without these rather harsh colors are Guy Nearing's "Guyencourt Hybrids" which are pubescens x keiskei. They have been given place names such as 'Brandywine', 'Chesapeake', 'Delaware', 'Hockessin', 'Lenape', and 'Montchanin'. They are all compact growing and useful in the front of the border. The flowers are small and do not make the great display of the other kinds that I have mentioned.
This brings us more or less into the season of R. carolinianum. This species is not as much appreciated as it deserves largely because most of the plants sent out have been of rather muddy lilac pink color. In any large collection good clear pinks and pure whites can be found. It is to be hoped that more nurserymen will more carefully select the plants they send out for the best forms and clear colors are certainly very very beautiful. As far as I know no selections have been propagated by cuttings, or sent out under clone names.
Between the season of the carolinianums and the "Ironclads" there come a host of hybrids of Rhododendron fortunei. We usually expect bloom from these by the 15th of May and they continue for some weeks. They are in general fast growing and many of them are very fragrant. While there are pure whites and fine reds in this group they are not yet generally available, and the prevailing colors are light pink to splendid rosy pink or to what some people call "watermelon pink." Varieties now available include 'Brookville', 'Caroline', 'Gloxineum', 'Halesite', 'Huntington', 'Mrs. W. R. Coe', 'Ramona', 'Scintillation', 'Skyglow', 'Westbury', 'Wheatley', and 'Wissahickon'.
This brings us to the season of the "Ironclads" which can be relied upon for a good display in years when most of the newer and much heralded varieties have had their flower buds injured or killed by prolonged zero or sub zero cold. I like better each year such varieties as 'Album' (often listed as catawbiense Album) 'Album Elegans', 'Atrosanguineum', 'Boule de Neige', 'Delicatissimum', 'Everestianum', 'Mrs. C. S. Sargent', 'Nova Zembla', 'Parsons Gloriosum', 'Purpureum Elegans', 'Roseum Superbum' and 'Sefton'. It would be easy to pick out several dozen more.
After the "Ironclads" comes a gap of one, two or more weeks before Rhododendron maximum really gets going and shows its real worth. Plants on a north slope and/or in very deep shade of course come into bloom last.
A splendid pink variety to fit in here is 'Midsummer' raised by J. Waterer & Crisp. Although it is rated H-3 it has been hardy with us.
This brings us to a magnificent late blooming pink Rhododendron which has been distributed in this area under the name 'Maximum Roseum'. Note the capital M, the capital R and the single quotes. They denote that this is a horticultural variety (or cultivar) and not a recognized botanical variety of the species R. maximum. The present name accepted by the International Rhododendron Registrar is 'Ponticum Roseum' and this seems to me equally confusing as it is not a recognized botanical variety of the species R. ponticum. Whatever its name and origin this plant is a "must" in every eastern collection of Rhododendrons.
Two other late blooming varieties should be noted although they are apparently not commercially available at the minute. They are 'Maxroseum' and 'Maxrubrum' and as the names indicate, one is pink and the other red.
At the International Rhododendron Conference in Portland in 1960, Dr. Clement Bowers mentioned a series of hybrids he had made at the Hicks Nursery in Long Island in the 1920's. He had used R. maximum with the hope of getting late flowering hybrids and had been disappointed in the results.
Judge Henry J. A. Collins a great Long Island Rhododendron enthusiast purchased some of the plants and after his death in 1952, Mrs. Collins gave them to the Planting Fields Arboretum. They are now large plants and their fine late bloom has attracted the attention of a number of members of the Rhododendron Society who feel that some of them may be worth introduction either for themselves or for their potential value for breeding.
I have been interested in these perhaps because I have been watching several similar series of hybrids at Swarthmore. We have two of Mr. Nearing's hybrids of maximum x discolor which year after year give us fine bloom in the period of the gap between the "Ironclads" and maximum. The College Commencement, the first or second Monday in June, nearly always falls in that period and that makes these forms particularly valuable to us.
With them, or shortly after, we have fine bloom on Mr. Dexter's hybrids between 'Lady Eleanor Cathcart' and decorum. The fine late flowers on the plants of these two groups encouraged us in the 1950's to use them as seed parents with pollen of some of our favorite "Ironclads." We used also various wild forms of R. maximum.
Many of the seedlings from these crosses are now coming into bloom at Commencement time when we need flowers most, so that we feel the time and effort we have put into producing them are already justified. I hope to report further on them in future years.