QBARS - v17n2 A Program of Rhododendron Hybridizing

A Program of Rhododendron Hybridizing
Joseph Casadeval, Whippany, New Jersey
A talk delivered to the Philadelphia Chapter of the ARS Jane 14, 1962

I first started working with azaleas in the spring of 1948. I bought a collection of Kurume azaleas that year and during the next few seasons I purchased a large number of Glenn Dales and others of this group. The general failure of these to flower eventually led to my hybridizing program. My main goal was to get a white azalea which would flower regularly year after year.
By 1958 three plants had been selected for further testing. These plants are good in habit and foliage and have fine white flowers. In my garden they proved hardier than any clone available in the trade.
Part of the program was a cross among the dwarf light colored Kurume and R. 'Mildred Mac', Mr. Gables hybrid ( R. yedoense var. poukhanense x R. ledifolium alba ). Some of these plants have a happy combination of the best of each of the parents. The selected clones have light flowers with various colored blotches. The flowers range from white with red, pink and lavender blotches, through shades of pale pink with dark blotches. A most attractive group of azaleas, some of which bloom ahead of R. yedoense var. poukhanense here. The selections seem to be exceedingly hardy and flower regularly. Another group of R. 'Louise Gable' hybrids with nice flowers in shades of pink and red, single, semi double and double types flower late in the season.
None of the above mentioned plants have been propagated as yet, but in the next year I expect to start with the best of the above, and they should extend the growing range of this group of azaleas.
The deciduous azaleas are well known and do extremely well here so I made a number of crosses with the Ghents, Japonicas and the Occidentale group. The crosses I grew on had a trace of fragrance, and some double flowers. About this time the first Knap Hill group came into the country. These new plants from England were so far advanced that it seemed futile to grow on the large quantities of Ghent or Japonica hybrids.
Another group of crosses were made involving the Rustica Flora Pleno group and the Knap Hills in color groups. Nothing worthwhile has flowered as yet. There are more to flower however. Some of the plants had bright red double flowers but they were no better than many others already in existence. I had a few rhododendrons around for years, but I never got very excited about them. In 1948 I visited the Arnold Arboretum to see the azaleas, and I left converted to rhododendrons. I must confess that even that limited collection seemed overwhelming to me. Later I visited the Dexter collection and even this mixed group of species and numbered seedlings seemed to me quite outstanding.
I made crosses of the large flowered plants with R. 'Roseum Elegans'. In time these flowered and the result was a mongrel group. Perhaps half had defective flowers, some even had no corollas, and others just never even opened up. This has happened in other crosses of R. 'Roseum Elegans'.

R. mucronulatum R. racemosum (F. 19,404)
Fig. 14. R. mucronulatum
R. Henny photo
Fig. 15. R. racemosum (F. 19404)
Very dwarf form.
Phetteplace photo

During the spring of 1951 I met Mr. Edmond Amateis of Brewster, New York. Many men have strongly influenced my thinking on rhododendron breeding, but none were to have the value that Edmond Amateis contributed. He very kindly shared his time, best plants, pollen and seeds, and answered all my questions. Several thousand plants can proudly claim Edmond as their stepfather. As a result of his suggestion I traced the records of the hybrids and then wrote to kind friends on the West coast for pollen from the best forms of species. Through Mr. Amateis I met Dave Leach who has been most helpful in the advice of where to get the best forms. Mr. Amateis's famous crosses of R. carolinianum led me to make many crosses on R. mucronulatum and R. carolinianum both the white and pink forms.
The crosses of R. carolinianum pink x R. mucronulatum var. 'Cornell Pink' and R. carolinianum album x R. mucronulatum var. 'Cornell Pink' produced a number of very fine colored hybrids. Several have been selected for growing on.
The cross of R. racemosum (Rock) (Fig. 15) x R. mucronulatum var. 'Cornell Pink' produced one very nice clear pink flowered hybrid. It is quite slow growing with bright red buds opening to bright pink, and very hardy as might be expected. One quite similar was raised from a group of R. 'Conemaugh' F2 hybrids. Of this group of over 200 seedlings only one came in a clear color.
Crosses made on selected forms of R. mucronulatum pollen sent from Oregon have in most cases been disappointing. So many came very poor in color, but there were pleasant surprises. R. mucronulatum x R. moupinense gave us some nice semi evergreen hybrids with white, pink and pale lavender bloom. These plants flower with R. mucronulatum and seem to be hardy enough to bloom here, but it is the F2 hybrids that we are waiting for.
R. mucronulatum x R. 'Bric-a-brac' has resulted in some fine small growing plants with pure white flowers as did the cross of R. mucronulatum x R. 'Valaspis'. R. mucronulatum x R. 'Valaspis' has also flowered a pale yellow with extremely heavy substance in its bloom. R. mucronulatum x R. lutescens all flowered pale pink. The best of the above will be selected and I hope to introduce the most distinctive in a fevv years. Meanwhile I have intercrossed and the F2 generation will be watched with interest. There are also a few plants with shades of blue flowers. One which I think better than R. 'Blue Tit' or R. 'Blue Diamond' and they seem hardy here. I don't have much patience with R. keiskei (Fig. 16) as I find that there is little substance in the bloom and in an effort to introduce this color a number of crosses were made with it and the best were R. 'Conemaugh' x R. keiskei (dwarf form). Perhaps a hundred plants flowered from this cross, several seem quite good. All are very hardy much more so than other crosses of this type.

R. keiskei
Fig. 16. R. keiskei, dwarf form
C. Smith photo

R. racemosum x R. keiskei just barely makes the winter here and is sterile. There is one tall growing selection with nice white flowers, also a dwarf growing selection quite similar to R. racemosum in habit and leaf with apricot bloom. There are also very fine foliage plants amongst this group. All have pollen and set seed well, and I have hopes in future generations here. This group of plants flower at a time when a plant has to be superior to attract notice because in many areas it will have to compete with the azaleas. The best of these should find a place further north where the evergreen azalea is not dependable.
Among the many R. carolinianum hybrids I must admit that I failed. Failed in that I didn't get many hybrids. Almost all were true R. carolinianum and all of them were very pretty. There are a few very dwarf hybrids of R. racemosum x R. carolinianum .
I have also made many crosses of the elepidotes. Like most every one else I raised a fair amount of Dexter hybrid seedlings. These seedlings were from selected, outstanding plants in each case. One of these seedlings won an Award at the New York Chapter Show as the best seedling there. It had a nice tall truss with flowers of good substance. Each of these trusses outlast the iron Clad types by a full week. There were a number of other plants which were set aside for observation, but as a group; they were a failure. Most of the seedlings raised from Dexter hybrids are very ordinary, and the chance of raising an individual better than the best already available is quite remote.
I became quite interested in raising nice red flowered hybrids, and also hoped for a good yellow. Not being able to grow vast numbers of seedlings to flowering size I carefully planned my program, hoping that the second or third generation would bring the desired result. After a careful study of all available writings I concluded that R. 'Vulcan' was a happy combination of a long line of good breeding, with the outstanding R. griersonianum . To date my tall growing red has been used in crosses with R. catawbiense and R. 'America' 'and others. Only small numbers of seedlings of each cross were raised to flowering, and none seem to be any hardier than R. 'Vulcan.' The color in a few has been a very brilliant red. Crosses were also made with R. 'Kluis Sensation', R. 'Armistice Day' and R. 'Queen Wilhemina' to introduce the best of the Dutch lines into a hardy group. Some of these seedlings are quite hardy, with the most hardy the least refined in color. We now have flowering plants incorporating the coloration of the above in a recessive form in most cases. Enough plants are being grown to select individuals with good habit for further breeding.
We are also growing several hundred plants of crosses with R. 'Earl of Donoughmore.' In the coming spring of 1963 we expect to cross the above flowering sized plants with R. 'Mars', R. 'Vulcan', and R. 'Beau Brummel'.
It seemed desirable to use R. forrestii as a parent, and there were already so many of the above listed that on the advice of Mr. H. L. Larson we decided on R. 'Elizabeth'' as the means of introducing R. forrestii into the program. A fairly large number of crosses were made between R. 'Elizabeth' and many hardy hybrids. Some were killed outright others grew too fast and were discarded. There are now blooming sized plants of R. 'Gamich' x R. 'Elizabeth', one of which has flowered, and had a good truss of 12-14 flowers of clear red. It had neither pollen nor would it set seed. There are small plants of R. 'America' x R. 'Elizabeth', R. 'Essex Scarlet' x R. 'Elizabeth' now old enough to bloom. In most cases the small growing and bushy plants were kept of each cross, since it is the dwarf bushy type of growth that interests us most.
Almost without exception crosses involving R. 'Elizabeth' have a floppy truss with various shades of red flowers. This is a group of plants raised for further breeding. It would be nice to get the desired goal in the F1 generation however. We still hope in any case they will be good for further work.
In starting a program for yellow and orange flowered hybrids much study was also done. Ten years ago I formulated a plan to actually construct a foundation for yellow and orange collored rhododendrons which would do well in our area. In the 1949 Rhododendron Yearbook of the R. H. S., Mr. O. C. A. Slocock set forth an outline for the breeding of yellow and orange colored hybrids. With this formula to guide us we felt that we should work for a plant whose habit would be compact and shapely; a leaf type and size which was in keeping with the style of plant which bore it; the flowers to be borne in a full and pleasing truss. The individual bloom must be flat faced and pure in color preferably with a bright gold blotch.
Parent plants were purchased in Oregon to make the first crosses. After much correspondence with friends it was decided that the main effort should be with R. 'Goldsworth Orange.' Several crosses were made using it as both seed and pollen parent. A flowering plant of R. 'Mrs. J. G. Millais' was also used. Crosses were made with R. 'Mrs. J. G. Millais' and R. 'Catawba Alba' and a hybrid from Mr. Gable R. 'Catawba' x discolor . A few plants of R. 'Catalga' x 'Lacteum Hybrid' and a cross of R. 'Catalga' x croceum hybrid were also carried on.
Some of the plants of each of the above crosses have flowered here. None were yellow, but some of the R. 'Goldsworth Orange' hybrids have flowered with some peach tinted bloom of generally poor quality. Some hybrids from R. 'Mrs. J. G. Millais' cross have been very fine. One plant from the cross of R. 'Catalga' x croceum hybrid had a fine upright truss with lovely white bloom, much after the form of R. croceum . Each flower was 3 inches in diameter, and many others will bloom this coming season 1963.
There are some very sturdy plants amongst the plants growing here of the crosses from R. 'Goldsworth Orange.' Most of the plants of this parentage will possibly flower in the spring of 1963. The above cross has grown so good that the crosses have been repeated, and I expect to grow on a much larger number. The British have reported very fine results from the use of R. 'Goldsworth Orange', also some rather nice plants of R. 'Goldsworth Yellow' hybrids are being grown. We expect to have bloom on most of these next spring. There are also plants involving R. 'Souvenir of W. C. Slocock' and R. 'Betty Robertson' being grown on. The plants of R. 'Souvenir of W. C. Slocock' x R. 'Roseum Elegans' are very fine in foliage and habit. I now regret that I did not use another parent instead of R. 'Roseum Elegans'.
The R. fortunei hybrids available 12 years ago seemed rather jumbled and I used in my program the well known hybrids R. 'Naomi' var. 'Exbury,' and R. 'Naomi' var. 'Neried.' The first flowerings of these hybrids have been very pleasing. Some very fine flowers in clear pink shades and white have been in evidence. The cross of R. 'Catalpa' x R. 'Naomi' var. 'Exbury' has shown some very fine bloom of heavy substance, all white. These as expected are large growing hybrids with flowers of an intermediate size between both parents.
For purple we used R. 'Purple Splendor' x R. 'Red Catawba'. I also used R. 'Sefton' with R. 'Purple Splendor.' Some of the plants have flowered and there are no colors as yet as outstanding as the parent. The balance should flower in 1963. The best of these R. 'Purple Splendor' x R. 'Red Catawba' will be crossed with the best seedling of R. 'Purple Splendor' x R. 'Sefton'. All these crosses seem to be bud hardy here, though the cross has lost the large blotch of the parent.
Pollen of R. 'Bowbells' was also used in several crosses. Most are indifferent, poor trusses and floppy flowers of mostly bad coloring. From a large number of seedlings some very nice hybrids have been selected. The best are very dwarf in habit, completely hardy and pure in color with a full truss. One selection is now ten years old is 10 inches high and 12 inches in diameter, with a full pink truss about 2½ x 2½ inches with the single floret about 1¼ inches in diameter. The leaves are about 2½ inches long and 1½ inches broad. It is not unusual to get the R. 'Bowbells' type hybrid even when crossed with the larger rhododendrons. For example a cross R. 'Catalga' x 'Bowbells' flowered plants of nearly normal R. 'Catalga' stature with a pure white bloom the size of R. 'Bowbells.' There is another plant from this cross that grows almost like the parent R. 'Bowbells' and has nearly circular leaves. There are plants with small leaves and 8 inch growths yearly, all out of scale with the hybrids of this cross. One additional reward of these plants is the very pretty new growth of some of the hybrids. This is a feature very new to most of us here on the East Coast.
To date I have put no plants on the market. All the hybrids that I have mentioned are for future recrossing, and they may be novel in breeding since many are now very complex hybrids. Very few of the elepidote hybrids are better garden plants than R. 'Roseum Elegans' or the whites better whites then are R. 'Boule de Neige' or R. 'Catawbiense Alba'. None of the reds are better than R. 'Charles Dickens' or R. 'America'. Their value lies in the fact that here are some hardy hybrids which will flower early in May three weeks ahead of the usual plants in our garden. The best characteristic is the long lasting flowers of good substance even in the hot drying winds of early May. There are also some very slow growing plants with habits which should appeal to the rock gardener. I feel that their greatest value lies in the fact that they will be stepping stones to the next generation. I am not alone in this; there are many others, some who grow many more plants than I do - others grow less, but all are in accord. Mr. Gable and Mr. Nearing are continuing their work. Dave Leach is doing a good work in Western Pennsylvania.
All of us are very well aware that there is a gap of many years between the planting of the seeds and the selection of the fine new hybrid. Possibly as many or more years will pass before some of these are available even to the connoisseur. The one sure way to get plants that I have mentioned is to make your own crosses and grow your own seedlings. The one reason that I am here tonight is to make a plea to you as members of this Chapter to get started either as individuals or in groups. A program such as I have outlined to you tonight is never done; each cross should be but one step toward your goal. We are a long way from selecting an All American rhododendron. We are even a long way from an all New Jersey or an all Eastern Pennsylvania rhododendron. The best and most successful way to get plants which grow in Philadelphia is to hybridize, grow and select them here. Then try to extend the area where they might grow.
Space and time should not be a limiting factor. I have raised the plants I spoke to you about tonight over a period of fourteen years. As for time I only have week ends and evenings for rhododendrons, garden visits, and the miscellaneous duties required for a family of seven children. As for the space, until a year ago I had a lot of 100 feet x 150 feet that was poorly drained. We find our new location on a sandy hillside with good air and water drainage, but no shade on the entire property save that of the home, and with a Southern and Western exposure the hillside gets winds from the west for unobstructed endless miles. Even with these handicaps the rhododendrons seem to do well enough. Shade trees are now planted and I think that a windbreak will have to be also. It is my hope that I have convinced some of you that you can grow some hybrids of your own making. There are many fine plants in many of your gardens that can be used as parents. Plants such as R. 'Bowbells'. R. 'Naomi', R. 'Mars' and many others. More unusual plants are on the West coast. Many of the plants Mr. Gable has raised would be worthy of further work. Mr. Nearing also has given us much of value.
There are many Japanese species of the R. ponticum series which are almost unknown in the East. A program of growing on and selecting the best forms of these plants is very much needed. There are crosses among the elepidotes which will give a large percentage of very good plants. Much time and effort has been wasted in the growing on of the Exbury and Knap Hill type azaleas of mixed seed. This entire group of plants will give a very small number of outstanding plants, even plants as good as the best of the Ghents. Seedlings of the Illams, a race of azaleas from New Zealand, offers a much greater chance of success to gardeners in the East.
Mr. Edmond Amateis has shown that R. carolinianum can be crossed with some degree of success, other crosses can be made with this species. During the past few years crosses involving the larger leaved rhododendrons have been made, and for the large shaded lot there may be space for plants of R. fictolacteum hybrids. One such cross flowered in New Jersey last spring.
In closing I may ask what are the rewards of such an undertaking: I suppose they vary with the individual. I doubt that fame or money would ever be the aim.