Rhododendron Breeding at Linswege
By Dietrich Hobbie
Linswege in Oldenburg Province is an ancient town. Only forty kilometers from the North Sea, the climate is damp and a little raw. The winters are frequently snowless and the fierce east winds may bring frosts of thirty below zero Centigrade. For centuries the farmers in Ammerland, the district in which Linswege lies, have cherished and cultivated the forests which have been there since time immemorial.
There are great stands of oak on the chalky subsoil and the adjacent heaths have been planted with Pinus sylvestris as far back as 1780. In these pine forests there is a luxurious undergrowth of Sorbus, Rhaninus, Quercus, and Vaccinium. With the introduction of rhododendron in the nineteenth century many areas within the undergrowth were cleared for the cultivation of these plants. In Westerstede, the Bohlje family were the first to grow rhododendron, in Rastede Friedrich Deus was the earliest, and in Edewecht G. D. Heinje pioneered. Others soon took up the culture of rhododendron, and in time this region became the most important continental center for the trading in rhododendrons and azaleas, second only to Boskoop in Holland. The old Waterer hybrids constituted the bulk of the varieties. Later some of the newer sorts introduced by Koster, van Nes, and den Ouden were added. A few of the Slocock varieties of the hardiest kinds were included. Then finally there were the German hybrids bred by the Seidel family. These are plants bred from R. catawbiense and degronianm, that are hardy in eastern Germany - and parts of Scandinavia. This comprised the bulk of the commercial varieties handled by the Oldenburg nurseries.
Fig. 14 R. williamsianum hybrids Fig. 15. R. 'H.C. Foerster'
The reports of the botanical expeditions into Tibet, Szechuan, Yunnan, Upper Burma and the Himalayas aroused much attention. During the nineteen twenties and thirties many new rhododendron species were brought into Germany to join the previously introduced species from Japan and America. About 1920 I first became interested in the propagation of rhododendron for commercial purpose, and began to raise species from seed. I read as much as I could find about rhododendron and found the Gardener's Chronicle and the Yearbooks of the Rhododendron Association especially exciting with their reports of the intensive hybridization work being conducted in England. It was not until 1937 that I was able to visit the great rhododendron gardens in Cornwall and southern England. There at Exbury, Lamellen and Kew I had my first glimpse of these magnificent hybrids in bloom. On the spot I resolved to start hybridizing. But where to start? My first attempts were seedlings derived from the English R. griffithianum and arboreum hybrids. Unfortunately a severe winter killed the young seedlings after a few seasons. However this unhappy ending convinced me of one thing: regardless of all other objectives, winter hardiness must come first.
Fig. 16. R. 'Gertrud Schäle' Fig. 17. R. williamsianum hybrids
In 1938 I had in bloom, in the greenhouse, a single plant of R. 'Britannia', a plant which is not quite winter hardy in this area. Outdoors, in my small collection of rhododendron, R. forrestii var. repens (hereinafter referred to as R. repens) had just opened its buds. This seemed like a natural! Using the anthers of R. repens, I pollinated the flowers of R. 'Britannia'. A little later in the season this same plant of R. 'Britannia' was to serve as the seed parent of a cross with R. williamsianum also. It was two years later though before it was possible to say with certainty that the seedlings were hybrids for only then did the characteristics of both parents become apparent.
My last packets of rhododendron seed from Professor Sir W. W. Smith of Edinburgh came in January, 1939. These were collected by the G. Sherriff expedition into southeast Tibet. Before the war I received seeds of both species and hybrids from Mr. Joseph B. Gable on many occasions. Both Mr. Gable and Professor Smith were exceedingly helpful with advice and their correspondence gave me much encouragement in my endeavors to create new rhododendron hybrids.
In 1941 I crossed R. 'Burgermeester Aarts' and R. 'Madame de Bruin' with R. williamsianum. (In all cases the seed parent is given first and the pollen parent last.) Today the offspring of this cross are specimens 1.7 meters high and as much through. The flowers of both hybrids vary from bright to deep rose. The first hybrid blooms a little earlier and its leaves are spoon shaped, it is probably the better hybrid. Although many of the seedlings suffer leaf burn and yellow in both winter and summer sun, they are quite hardy. About forty per cent of the seedlings are quite insensitive to sunlight. The new growth appearing after the blooms is especially attractive; it is of a leathery appearance with a color ranging from red-orange to pink and often rivals the floral display. It lasts from ten to fourteen days, then gradually turns green. However this color does not appear with equal intensity every season. This phenomenon is most pronounced with the hybrids of R. williamsianum.
In 1942 the following crosses were made: 'R. Canary' x repens, R. 'America' x repens, R. 'Essex Scarlet' x repens ('R. Elizabeth Hobbie'), R. 'Mad. de Bruin' x repens (R. 'Ostfriesland'). There are now several hundred seedlings of these combinations; the finest flowering and the hardiest are being propagated. The cross 'R. Canary' x repens produced some astonishingly hardy offspring, but also quite a number of deformed plants. A few of the seedlings have glowing orange scarlet flowers; three of the plants are being propagated. The hybrids derived from 'R. America' bloom in shades of carmine and scarlet, but the 'Elizabeth Hobbie' cross produced remarkably hardier plants. The appearance of offspring hardier than the parents has occurred in many combinations; and though I have seen it many times, I am always surprised by its recurrence.
In this same year I made hybrids of R. 'Goldsworth Yellow', 'Cunningham's Sulfur', 'America', 'Essex Scarlet', and 'Prometheus' with R. williamsianum. Several hundred specimens of these hybrids remain in my nursery, the hardiest and most beautiful resulted from R. 'Goldsworth Yellow' and 'Essex Scarlet'. The selected plants out of the R. 'Goldsworth Yellow' cross are hardy and have yellow orange flowers. They are now, dense, well rounded shrubs about eighty centimeters high and about one hundred centimeters across. About half of the seedlings resulting from R. 'Prometheus' and 'America' are quite sensitive to light.
A number of crosses using R. discolor as pollen parent were also made in this year. The seed parents were R. 'Catherine van Tol', 'Caractacus', 'Mrs. R. S. Holford', 'John Walter', 'Catawbiense Grandiflorum', 'Professor Hugo de Vries', 'Madame Masson', and 'James Nashmyth'. Out of these combinations the best hybrids resulted from 'R. Catherine van Tol', 'John Walter', and 'James Nashmyth'. Most of the seedlings are rather free blooming. The trusses are fairly large, bearing flowers in shades of pink or mauve. All of the hybrids from R. discolor are scented, hardiness is about that of R. 'Mrs. P. den Ouden', while the blooming period follows the latest of the Catawba hybrids.
A few hundred seedlings of the 1943 crosses remain in the nursery. These are derived from 'R. Jacksonii', sanguineum and 'Adriaan Koster' using R. williamsianum as pollen parent. Most of these are dense shrubs about seventy to eighty centimeters through and fifty or sixty high. In general the leaves are a little smaller than either parent. Like its parent, the hybrid derived from 'R. Jacksonii' blooms at the end of April bearing apple-blossom pink trusses of eight to twelve flowers. In Oldenburg the plants are winter hardy.
The other combinations made in 1913 gave no hybrids with outstanding qualities.
In 1944, again using R. williamsianum as pollen parent, crosses were made on R. 'Duke of York', 'Hassan', and 'Homer'. The hybrids derived from R. 'Duke of York' has bronzy-colored new growth, very pretty old rose flowers, and a dense compact habit of growth. Some of the flowers have seven petals. Unfortunately, this hybrid, like many others with R. fortunei blood in their breeding, is a rather sparse bloomer when young. 'R. Hassan' x williamsianum produces strikingly-colored new growths, the upright trusses are compact and of a wonderful rosy pink.
Because of the war it was not possible to continue the hybridization work until 1946. In that year R. repens (as pollen donor) was crossed with R. 'Prometheus' (R. 'Gertrude Schale'), 'Purple Splendor', 'Dr. V. H. Rutgers', 'Earl of Athlone', (R. 'Ursula Siems'), 'Edward S. Rand', and 'Britannia' (R. 'Linswegeanum'). The most valuable of these are R. 'Gertrude Schale' and 'Ursula Siems.' Three thousand seedlings resulted from the 'Gertrude Schale' cross; a thousand of these were either tender, or else had to be destroyed because the foliage was disfigured by the winter weather. Another thousand were gradually eliminated by 1956, while from the balance six were finally selected. These selected forms bear magnificent scarlet flowers and will be introduced eventually. R. 'Ursula Siems' is a plant unexcelled for color and profusion of bloom. Outdoors, the plan's are in bloom by the middle of April which is rather early for this region. I believe that the greatest value of this hybrid lies in its future as a forcing plant. About fifteen forms remain out of several hundred seedlings of this cross. Until the spring of 1956 there were several hundred plants resulting from the cross R. 'Dr. V. H. Rutgers' x repens. These were splendid sturdy shrubs about forty to sixty centimeters high and some of them were quite hardy. However the majority of them suffered from a fatal defect. The edge of the corolla burnt in the sunlight and turned black; this behavior is especially characteristic in plants bearing intensely pigmented flowers. By May of 1956 it was clear that only about fifteen or twenty of the seedlings would bear normal flowers of a purplish red color. All others were destroyed. Likewise the offspring of the hybrids from R. 'Edward S. Rand' and 'Caractacus' were destroyed since they were of no value. On the other hand with R. williamsianum as pollen parent, R. 'Dr. V. H. Rutgers' produced extremely floriferous plants blooming mostly in shades of purplish pink.
In addition, still using R. williamsianum as pollen parent, crosses were made on 'R. Caractacus', 'Canary', 'Edward S. Rand', 'Professor Hugo de Vries', 'Doncaster', 'Eidam', 'Mrs. Lindsay Smith', astrocalyx, 'Faggetter's Favorite', 'Corona' (R. 'Bow Bells'), 'Kate Waterer', 'Madame Fr. J. Chauvin', 'Poot', 'James Marshall Brooks', 'Antoon van Welie', and 'B. de Bruin'. The best offspring are derived from R. 'Caractacus' with reddish purple new growth and flower buds, flowers reddish purple; and from 'R. Doncaster' with reddish purple flower buds, cherry red flowers, especially hardy and of rather dense growth. The prettiest of these combinations is with R. 'Madame Fr. J. Chauvin'. This is a somewhat laxer growth, blooming in mid-May large splendid pure rose flowers that are frequently edged with a somewhat deeper tint. Unfortunately many of these seedlings suffer slightly during a severe winter such as occurred here in 1956. However by the end of the summer all signs of damage have disappeared and the plants are covered with buds.
Fig. 18. R. 'Suomi' Fig. 19. R. Metternianus
In 1947 I hybridized R. 'Professor F. Bettex' x williamsianum, 'Mrs. Butler' x williamsianum ('R. Psyche'), 'Bismarck' x williamsianum. 'Helene Schiffner' x williamsianum, discolor x williamsianum (R. 'Oldenburg'), (wightii x caucasicum stramineum) x williamsianum (very hardy and having flowers of a silky texture), 'Madame Masson' x williamsianum, wardii x williamsianum, Catawbiense compactum (from Joseph B. Gable) x williamsianum didymum x williamsianum, metternianus* (a very hardy and attractive form of degronianum) x williamsianum, astrocalgx x repens, (catawbiense x thomsonii) x repens, 'Britannia' x repens) x williamsianum (R. 'Dr. H. C. Karl Foerster'), 'Staring' x williamsianum, 'Genoveva' x williamsianum, 'Louis Pasteur' x williamsianum, 'Catherine van Tol' x williamsianum, wardii (G. Sherriff 5679) x williamsianum, plus a miscellany of Catawba hybrids x williamsianum.
Hybrids of R. 'Professor F. Bettex' bloom bright red in May, but over half of the seedlings develop black spots on the leaves during the winter, and therefore had to be destroyed. 'R. Oldenburg' is a cross wherein the seedlings are practically one hundred per cent uniform. A bronzy tint appears on the new growths, and this is the latest blooming of all of the R. williamsianum hybrids. The individual flowers average ten centimeters in diameter, they are colored a delicate pink, and are seven petaled. Hardiness is about B, and the flowers are fragrant. Likewise, R. 'Psyche' has very large flowers with a somewhat weaker fragrance. It is rather characteristic that the hybrids of R. discolor, and of R. fortunei, too, give vigorous F1 seedlings, however the uniformity is rather disturbing, while the failure to bloom readily in the juvenile state is a distinct defect. Most of the other R. williamsianum hybrids are rather free flowering while young. Here I might add that most hybrids of R. repens are much freer flowering than the species. I have noted that in general only one-fourth R. repens blood will suffice to confer the quality of free and early bloom; similarly for the hybrids of R. williamsianum. I hasten to qualify that this may be extremely variable in some individual cases. Of the 1947 combinations the most floriferous were the somewhat tender R. 'Staring' x williamsianum, 'Poot' x williamsianum, and Dr. 'H. C. Karl Foerster'.
* These plants originated from seed that was obtained in 1937 from K. Wada of the Hakoneya Nurseries in Japan and are not to be confused with R. metternichii. The seed was given to Mr. Hobbie by J. P. Mager in the original containers and these were labeled R. Metternianus. In a catalog of the Hakoneya Nurseries, Mr. Hobbie found the description: "A very hardy and attractive form of R. degronianum.- Mr. Hobbie states further that he has searched the botanical literature but has never found any reference to R. Metternianus. Mr. Hobbie also sent a leaf from this R. Metternianus and one from R. degronianum. The former leaf has only the vestigal traces of a heavy faun-colored indumentum that occurs on the latter. This indumentum is in fact so thick on R. degronianum that it obscures all signs of the veins on the underside that are plainly seen on the other. I sent these leaves to Dr. Bowers with the suggestion that a morphological examination be made of the plant called R. Metternianus. Apparently this is a hybrid for Mr. Hobbie tells me that this plant bears six lobed flowers. Apparently it is not the type form of either R. degronianum or R.metternichii.
* R. Ammerlandense = R. 'Britannia' x williamsianum
Eighty combinations were bred in 1948. To mention but a few: R. chrysanthum x repens, ('Britannia' x repens) x metternianum ('R. Suomi'), sutchuense x williamsianum, oreodoxa x williamsianum, oreodoxa x repens, 'Jacksonii' x 'Linswegeanum,' Ammerlandense* x repens, Ammerlandense x astrocalyx, 'Campdis' x willianisianum, 'Mrs. P. den Ouden' x williamsianum, 'von Oheimb Woislowitz' x williamsianum, insigne x 'Louis Pasteur,' insigne x 'Antoon van Welie', 'Duke of York' x griersonianum, 'Duke of York' x venator. Of these probably the most important cross for future hybridization work is R. chrysanthum x repens. Twelve seedlings have bloomed for the last two years bearing fine brick red flowers. In this cross the extreme hardiness is combined with a tendency toward free flowering together with the red and yellow pigmentation; certainly a most desirable combination of qualities for further breeding. Using this cross as a parent, there are already seedlings employing as the other partner R. 'Prometheus', wardii, 'Polarstar', and astrocalyx. The hybrid R. 'Suomi' combine good winter hardiness with a great tendency to flower freely in a color that ranges from deep rose to brilliant scarlet. After fourteen days the scarlet color gradually changes to a deep pink or a yellowish pink. This hybrid holds its blooms for a longer time than any other rhododendron that I know of. I consider 'R. Suomi' to be a very promising rhododendron for Scandanavia and those parts of the United States where the winters are severe. Here it may be noted that R. metternianus confers great winter hardiness even when crossed with such tender species as R. griersonianum and dichroanthum.
Fig. 20. R. 'Elizabeth Hobbie' Fig. 21. R. 'Burgermeester Aarts'
Fig. 22. R. chrysanthum
All photos by Hobbie
In 1949 on a visit to some of the large rhododendron gardens in England and Scotland I collected pollen of some of the more interesting species and hybrids for crossing with certain selected winter hardy hybrids of my own breeding. This collection included among others pollen from hybrids derived from R. griffithianum, griersonianum, venator, auriculatum, haematodes, neriiflorum, cerasinum, and the hybrids 'Vega', 'Francis Hanger', 'Dainty', 'Aspansia', and 'May Day'.
At least half of the seedlings from these crosses were killed in the winter of 1956. At the time these crosses were made I was not sufficiently appreciative of the various degrees of winter hardiness and failed to realize that only the hardiest would be worth breeding to such relatively tender varieties if hardy offspring were desired. In my experience there is little chance for the tender sorts to give offspring suitably hardy for the continental climate unless they are combined with the most reliably hardy species and hybrids among which I include R. chrysanthum and its hybrids, smirnowii, 'Catalgla', catawbiense compactum, brachycarpum, some selected clones of fortunei, brachycarpum montnaum, brachycarpum montanum lutescens, caucasicum in its hardiest forms, maximum and the hardiest hybrids.
Starting in 1950 it was possible for the first time to use my own hybrids of R. williamsianum and repens as breeding partners. Out of a total of sixty crosses, twelve employed such hybrids for one parent and hardy Waterer hybrids on the other. Other crosses were made using R. wardii, astrocalyx, puralbum, and souliei. Many seedlings from the collections of G. Sherriff, Professor Hu, and Dr. Schafer were in bloom for the first time and the best of these were used in further breeding. R. wardii, Sherriff 5679, has been used extensively because of its fine yellow color. In most combinations this form of R. wardii gives very free flowering offspring.
The year 1950 also marked the inception of a new breeding project. At the suggestion of Mr. Fritz Heiler, the garden director of the city of Munich, I began breeding rhododendron which would be more tolerant of alkaline soils. Although this work is still in the initial stages, the preliminary results look as if there might be some hope in this direction.
In 1951 one hundred and thirty six combinations were made. Of these I shall enumerate only the most interesting: R. 'Dr. V. H. Rutgers' x aperantum, 'Dr. H. C. Dresselhuys' x williamsianum hybrids, 'Dr. H. C. Dresselhuys' x repens hybrids, ambiguum x concatenans, catawbiense rubrum x repens, 'Catalgla' x repens, wardii x haemaleum, 'America' x ('Mad. de Bruin' x repens), Metternianus x orbiculare, 'Catalgla' x griersonianum (hardy!), 'Catalgla' x dichroanthum aff. Sherriff, Metternianus x dichroanthum aff. Sherriff, 'Catherine van Tol' x repens hybrids, 'Goldsworth Yellow' x wardii, wardii x scyphocalyx, wardii x herpesticum, 'John Walter' x aperantum, and chrysanthum x campylocarpum (hardy!).
During 1952 I concentrated on four-way hybrids such as for example (R. 'Britannia' x repens) x ('Britannia' x smirnowii) About one hundred and twenty five crosses were made focusing attention on the problem of tolerance to alkaline soils and plants of even greater winter hardiness. In addition R. carolinianum and some other lepidotes were used in the hybridization work. A hybrid of R. carolinianum with R. ciliatum has already bloomed here and it exhibits a good degree of winter hardiness even though R. ciliatum is not at all hardy here. There is also a hybrid R. carolinianum x lutescens, similarly hardy and bearing a good number of pale yellow flowers.
In 1953 the number of crosses was fifty nine. It was now possible in view of the previous experience to plan precise directed crosses. These were aimed at the further development of Rhododendrons tolerant of alkali, and again it seemed as if fully hardy plants for the colder regions merited further attention. For this latter objective the following were used mainly: R. 'Catalgla',' 'Catalgla' hybrids, catawbiense rubrum, brachycarpum aff. from Korea (a form hardy in Mustila, Finland), chrysanthum, chrysanthum hybrids, brachycarpum montanum lutescens, insigne, traillianum, puralbum, repens, williamsianum hybrids, Metternianus, oreodoxa, and the hardiest Seidel hybrids.
In 1954 only thirty six crosses were made concentrating on winter hardy hybrids of R. 'Catalgla' x chrysanthum, fortunei x chrysanthum, and fortunei x brachycarpum montanum lutescens with the intention of producing creamy yellow blooming plants of dense bushy habit and completely winter hardy. It was now possible to use the hybrids already created here for certain specific objectives. Where pollen of a required plant was lacking, it was readily supplied by breeders in England and in other parts of the world.
In the meanwhile the number of seedlings has increased to almost a quarter of a million. Selection and transplanting require a great amount of time and considerable space. The first selections of all this effort are now being propagated in Germany and Holland. Propagators for other selections will he designated in England and the United States as soon as the other hybrids have been properly evaluated and tested. Many thousands of welcome visitors from all parts of the world come to Linswege each year. I hope that my work with the rhododendrons will strengthen the bonds of peace and friendship with the people of many countries so that these magnificent plants may be enjoyed by all.