Hardy Rhododendrons for Colder Climates
Edmund Amateis, Clermont, Florida
The title is indecisive. How hardy? Colder than what? Hardiness ratings and zones of hardiness are helpful but are not definitive, as so many different factors play their parts. One, which is of utmost importance, is air drainage. Neighbors of mine who live only a few miles away but at a considerably higher elevation are able to grow things that are not at all satisfactory with me.
The past winter, for instance, was one of the worst ever experienced in the Northeast, with temperatures to -24° F. yet, due to a heavy snow covering, those plants that are covered will come through in better condition than usual. Bill Efinger, my neighbor in Brewster, has just written me the following report, "The snow has now mostly melted and I have been surveying the damage. In my own nursery I have lost practically all buds on red rhododendrons, even when they were under snow. Also lost is Boursault. I went to your place and cut buds high up on the plants above the snow line. In this report blasted means 100% blasted.
|schlippenbachii , blasted||'Lady Armstrong,' some pips gone||'Daviesii', blasted|
|mucronulatum , partly blasted||carolinianum , blasted||'Windbeam', blasted|
|'Boule de Neige', blasted||'Mrs. C. S. Sargent', some pips gone||'Praecox', O.K.|
|'Roseum Elegans', few pips gone||'Ignatius Sargent', blasted||'Dora Amateis', O.K.|
This plant, R. 'Dora Amateis', is actually still under snow except for one top branch from which I took the bud. However, we got our very low temperatures right after storm No. 2 at which time there were a few top branches still exposed. So while this may not be completely conclusive it is the best news of the season anyway, particularly in light of what happened to the buds on my reds under the snow."
(Bill Efinger's elation over R. 'Dora Amateis' is undoubtedly prompted by the fact that he and Warren Baldsiefen are propagating it for eventual introduction). Perhaps a fairly accurate understanding of temperatures at my place can be had when I say that, for the past thirty years and except for a few seasons, peaches have failed and forsythias are erratic bloomers. In the breeding of rhododendrons I have striven for flower-bud hardiness to meet these conditions.
I wish I could speak from a longer period of experience in breeding than twelve years but if some of my findings can be of help to other breeders who are striving for hardiness, this article will then be worth the effort. In the beginning I used, for the hardy parent, what was available such as R. 'A. Lincoln', 'Delicatissimum', 'Everestianum' etc. in the hybrids and maximum and carolinianum in the species. The white form of catawbiense , which was discovered by Powell Glass, was used as soon as it started to bloom. This was the third generation raised from seeds obtained from Joe Gable.
The breeder who is not satisfied with primary crosses, as an end product, has at his disposal, by past breeders, very few crosses with hardy blood that can be of much help. R. 'Lady Eleanor Cathcart' and R. 'Praecox' immediately suggest themselves, also 'Russellianum', 'Clivianum' and 'Manglesii', which probably would be hard to find. Generally speaking we have to make our own primary crosses for further development and that means an additional five or six years of waiting. I have wondered, too, how Waterer and the other early English breeders obtained their results. Line breeding was a well-established practice at that time. The tenderness of some of the "ironclads" would indicate a primary cross whereas the hardiness of R. 'Roseum Elegans' suggests second generation segregation. This, of course, is pure speculation.
In my own case and until they have been tested over a longer period, I cannot say that one infusion of hardy blood with the tenderer Asiatics is sufficient to produce hardiness for my place. So far, with a few exceptions, such crosses have proven no hardier than the average ironclad. A winter of -15 to -20 without snow protection will tell the story. The cross carolinianum x bullatum is hopelessly tender and is strictly a greenhouse plant. carolinianum x edgeworthii is probably too tender for the New York area. but is now being tested in Richmond by Dr. Wheeldon. carolinianum x ciliatum ('Dora Amateis'), already mentioned, very surprisingly has proven hardier than its hardiest parent. All three of these crosses are sterile which prevents further development. R. ciliatum proved itself a good parent also in 'Praecox'. (It seems to me that if 'Praecox' were selfed one might expect a good, fragrant, hardy early-blooming white). Many of my crosses have yet to bloom so it is difficult to be conclusive about any of them but it has been my observation that yellow is definitely recessive. [( lacteum x 'Loderi') x ( lacteum x 'M. Swaythling)'], a Halfdan Lem cross, has a blossom as yellow as a jonquil. Crossed with catawbiense album Glass the result was a large, beautifully frilled flower only a light cream in color. Catawbiense album Glass x 'Penjerrick', catawbiense album Glass x campylocarpum var. hookeri and brachycarpum x campylocarpum also failed to produce more than a cream. In an attempt for the hardy yellow I have now doubled the factors of yellow and hardiness by crossing ( catawbiense album Glass x campylocarpum ) [ catawbiense album Glass x [( lacteum x Loderi) x ( lacteum x 'M. Swaythling')]. Out of about a hundred Elizabeth crosses, many of them with catawbiense var. rubrum as the hardy parent, there are a half dozen or so that show possibilities with further testing. Only one good dwarf appeared.
In the carotene group R. dichroanthum has produced gratifying results - for other breeders as well as myself. A cross of catawbiense album Glass with Hejlmar Larson's cross [('Nereid' x fortunei ) x 'Fabia')] resulted in a ruffled apricot with large yellow sepals. Others are peach, terra cotta, etc. It is my guess that someday somebody is going to produce a fine hardy yellow that will have dichroanthum in its ancestry. A parent that has performed beautifully is 'Mrs. C. S. Sargent'. The cross 'Mrs. C. S. Sargent' by the yellow Dexter hybrid, R. 'C.O.D.', resulted in a large blossom of a fine, warm glowing pink.
We now come to R. maximum , vilified and belittled, as a parent, by every breeder I have spoken with. I must confess I am at a complete loss to understand why any experienced breeder should expect phenomenal results from a primary cross. If a primary maximum cross has not yet produced a R. 'Beauty of Littleworth' or a 'Loderi', neither has catawbiense . I have yet to see even a good clean red with catawbiense blood in it. Probably now, with 'Powell Glass' or some other true-breeding white forms of catawbiense , the results might be different. In passing, I would like to say that I believe that catawbiense , in its purity, should be used as a parent for hardiness. I know of no catawbiense hybrid that surpasses its parent in hardiness. My results so far with R. maximum have been happy, for I find that it lends itself to breeding with an acquiescence that is delightfully feminine. While it transmits the desirable quality of hardiness in quantity it does not pass on its large plant size or late blooming. Even the primary cross of maximum x arboreum ('Lady Eleanor Cathcart') has not only an unusual and distinguished habit of growth but also fine blossoms that have proved hardy at 5 F. (Why has no one ever selfed or back-crossed this plant?) Another at Brewster is Gable's maximum x 'Essex Scarlet' that I have used a great deal in my breeding. It has a fine, large, hardy truss of pure red, a sort of Turkey red, without a trace of blue. My own crosses of maximum x 'Jasper' and maximum x Fabia, both quite dwarf, are not without merit. R. maximum x R. discolor , even as a primary has produced one outstanding plant. Interestingly enough, all of these crosses bloom before they put out their new foliage. My most recent maximum cross was ( maximum x 'Essex Scarlet') x ( maximum x arboreum ). Here again I have doubled up on both hardiness and red factors. Theoretically this cross, somewhere along the line, should produce a good red of purity, coupled with extreme hardiness.
Catawbiense var. rubrum gave the poorest performance of any hardy parent used. R. brachycarpum , was no great shakes as a parent, being too long in coming into bloom. 'Abe Lincoln' x 'Earl of Athlone' produced disappointing results though possibly with another mate the Earl might perform more nobly. R. 'Pygmalion', too, failed to cut the figure I expected.
Strange things have happened in my short experience, one of the most unusual, in a cross of kalmia latifolia x kalmia angustifolia . The result was angustifolia , pure and simple. This was not a case of apomixy, for latifolia was the seed parent. In other words, latifolia accepted foreign pollen, produced viable seeds yet had no influence on the progeny. As this cross is sterile, further development has been impossible.
o far I have found that primary crosses in rhododendrons produce quite variable seedlings, breaking up in what would appear to be second generation segregation. Unlike the well-behaved pea and snapdragon of Mendel, they refuse to lend themselves to neat little mathematical ratios. On only one occasion have I seen consistent uniformity in a primary cross. This was a Leach cross, catawbiense album Glass x yakushimanum . It was a joy to behold. All so uniform in height that they looked sheared and each smothered with its merry pink buds and white blossoms. Warren Baldsiefen is now propagating a cross made by Joe Gable of maximum x haematodes that resulted in a yellow. The yellow might be explained as an aberration of the plastids but such deductions after the fact are small help to a man trying for a red. Knowing how dominant purple is I thought to drift with the tide and try for an outstanding hardy purple or lavender, so I crossed R. 'Everestianum' with 'Van Ness Sensation'. The result was pink! It is nevertheless an outstanding plant of spreading growth that after five years of testing has proven itself to be a floriferous annual bloomer of great hardiness. Its hardiness must be due to a fortunate combination of the hardiness, of R. catawbiense in R. 'Everestianum' and the R. maximum in R. 'Van Ness Sensation'. Baldsiefen is now propagating this plant. In striving for a yellow I crossed catawbiense album Glass with Larson's cross, [( campylocarpum x fortunei ) x croceum ). Again the result was pink.
When one considers that the precise Mendelian ratios in F2 crosses has been accomplished with intra-specific crosses, that is, different forms of the same species such as red x white peas, white x black rabbits etc. one can speculate if variability in rhododendrons could not be due to the fact that we are making intra-specific crosses. I have presented this conjecture to several geneticists who assure me that I am wrong. Possibly so, but as yet they have not proven to me that they are right. I would like very much to see the results of a second generation mating between different species of rabbits or mice. Conversely, an intra-specific cross between different forms of the same species of rhododendron might tell a story. Whatever the cause, an unstable genus, playful plastids or ecological conditions, the science of genetics becomes, at this point, a game of chance. So gently and reverently, I put my books of genetics back on their shelves. I say reverently for I have a profound respect for the science of genetics. But I fail to see how a priori reasoning can assist one in the practical breeding of rhododendrons. It might explain results but until our geneticists can control the desired genes, in rhododendrons, as Dr. Morgan did with his pink-eyed fruit flies, we will not be able to prognosticate results. This statement does not apply to the intra-specific crosses made in the production of hybrid corn, which result in great uniformity.
While I am at it, I suppose I may as well die for a sheep as a lamb by saying that inbreeding has no terrors for me. I don't advocate it but when necessity demands, I don't hesitate. The most elementary principle of Mendelism requires the inbreeding of a primary cross. There was, for instance, no way of producing 'Powell Glass' except by sibling crosses. After five generations I detect no loss of vigor. Theoretically, if bad genes produce bad results with uncontrolled breeding why shouldn't good genes produce good results with controlled breeding? Arabians have been line breeding their horse for eight hundred years without loss of vigor. Every breed of cattle and every breed of dogs is the result of sports or breeding and their purity surely was not maintained with the introduction of foreign blood. Kalmia is very neatly designed for self pollenizing as are all the legumes. All the millions of English sparrows and starlings in our country are descendants of a few pairs released in N.Y., all are inbred and I am sure no one questions their vitality. The Jukes and the Kallikaks are held up to us as horrible examples of uncontrolled inbreeding but no one has mentioned the Ptolemies who for thirty generations practiced brother-sister marriages and remained vigorous enough to control Egypt for that period of time.
In closing I would like to say that in thirty years of gardening my greatest pleasures came with breeding. The average nurseryman is much too busy to breed, so new and better varieties must come, in part, from the amateur. Breeding is not difficult. Due to the variability of rhododendrons good results are sometimes obtained from primary crosses. A policy of primary crosses would undoubtedly require large plantings and unless each factor from each parent is equal there will most probably be an equalizing effect so that any gain from the one would be a loss from the other parent. An understanding of the elementary principles of segregation will suffice so don't be intimidated by the profundities of genetics. As there is yet no way of controlling segregation, crossovers, linkage etc., I see no reason to confuse yourself. But if you are of an inquiring mind then by all means studying it is fascinating. Bear in mind that man has been breeding long before Mendel was born. Parenthetically, might I say, that it is regrettable that man has not devoted as much time and effort toward improving himself as he has his dogs and cattle. Have a goal, plan as carefully as you can within the limitations of your material and as Nearing says, have the courage to discard. Much worthless stuff will appear in the grab bag of your hopes and efforts. Don't be afraid of mistakes. They are made by the best. Listen to what Aristotle has to say. "The sex of sheep depends upon the direction in which the parents were facing at the time of mating. If they faced north the offspring will be male but if south, then they will be females." It does seem as if he could have run a few tests before rushing into print, but then, the period of gestation would demand a wait too long for any author. He never did say what would happen if they faced east or west.