Joseph B. Brueckner - Mississauga, Ontario
RHODODENDRONS: A SEARCH FOR STRENGTH WITH BEAUTY
|But here the simplicity factor in
my conclusion ends. Years of correspondence followed. First I wrote to
nurseries, then to arboretums, botanical gardens. Yes, most nurseries had
RR. mucronulatum, some even had indeterminate dauricums, but none had parvifolium,
Siberian aureum, dauricum (like var. sempervirens), lapponicum, to say
nothing of the Tigerstedt subspecies of brachycarpum.
It was a lengthy search, until I had three breaks. Dietrich Hobbie kindly wrote me that he had come across an erect-growing R. lapponicum in the Great Slave Lake area of Canada, where it grew knee high. Orlando Pride offered me a plant, a very hardy R. brachycarpum, grown from seed, which he received years ago from Finland and, if I am not mistaken, from Tigerstedt himself. Finally, I established contact with Vladimir Vasak, a Czechoslovakian botanist who collected plants in the Soviet Union for the Praha Botanical Garden.
Use was made of these sources and enough material obtained for breeding hardy hybrids. However, even after overcoming these initial problems, the breeding of satisfactory - and it must be emphasized, SATISFACTORY hybrids, did not prove to be as simple as was envisioned. Plants growing in the Arctic or at high elevations have a short growing season. Also, the winter may quite suddenly turn into summer. Once there are a few mild days the summer for them has arrived. They cannot hesitate much, they start moving. Moreover, to utilize the short time span to the utmost, the foliage unfolds at the same time the flower buds do. Both create a problem within the horticultural context. We have a few mild days in succession in January or even in March, the buds are forced into growth, then the winter returns and we have no flowers.
However, the situation is not entirely hopeless. Clones, or even the whole grex in some instances, may not be affected by any of these disadvantages. One should be able to find satisfactory plants with even greater frequency in the second generation hybrids. But all this needs much time and observation before a satisfying selection can be made.
To bring order to this communication, let's first deal with lepidote hybrids, and foremost of all, with the descendents of R. lapponicum, the truly arctic species with which I spent so much of my time in my breeding project.
The two plants of R. lapponicum that I received from the Great Slave Lake area survived a number of years, though not happily in Mississauga. In fact, the last of the two died a year ago. It is a very difficult plant to use within a breeding project, but even so, it was possible to obtain nineteen hybrids.
Some of these hybrids probably have a good horticultural potential, as for example, R. lapponicum X dauricum. It should be noted that this (or others of similar parentage) could possibly be the hardiest rhododendron hybrids, theoretically at least, one can create. In this particular grex a remarkable variation amongst the individual clones, with regard to stature, foliage and flower colour can be noted, unusual when two species are crossed. The explanation lies in R. dauricum, the pollen parent, a hybrid in itself. It is the result of a cross of Dr. Gustav Mehlquist's of a white form with a dwarf purplish-pink form of R. dauricum.
R. chryseum x lapponicum is, on the other hand, a textbook example of a species to species cross. All clones are identical, and during years of observation I could not detect any variation amongst them in any respect. All have cyclamen-pink flowers, are equally floriferous, and the flowers exude a delicate and delightful perfume, especially noticeable in a mass planting on a sunny afternoon.
RR. campylogynum, racemosum, calostrotum (Gigha form), carolinianum and others also gave good results. To describe them, even briefly, would however be beyond the scope of this paper.
With due regard for all the efforts that were concentrated upon R. lapponicum, R. dauricum, which is represented by several forms in my collection, was not neglected. Neither were RR. carolinianum, in both its pink and white forms, ferrugineum and some other species and/or hybrids that could contribute their hardiness to the offspring produced. The first that comes to my mind is a cross of R. dauricum var. sempervirens with a R. augustinii hybrid. The best two clones selected, and especially one of them, are vigorous, tall-growing shrubs with large light-lobelia-blue flowers. These contrast impressively with the light yellowish-green fresh growth. Hybrids produced with another form of R. dauricum, deciduous, (collected in Siberia by Vasak) and R. impeditum are dwarf with violet flowers and a good green, dense foliage.
R. calostrotum (Gigha) x dauricum var. album is a neat dwarf floriferous bush with somewhat greyish-green foliage and large cyclamen-purple flowers with a conspicuous ruby-red blotch. Of the many dauricum hybrids, two more ought to be mentioned. R. dauricum var. album X fletcherianum is covered with huge creamy-white flowers in early Spring, hiding the evergreen foliage. After they fade, the medium-sized bush remains a delight to look at all year round, clothed in its lush green foliage. Never have I seen a rhododendron grow so fast, at a rate of up to 60 cm per year, as an open-pollinated seedling of R. dauricum var. sempervirens. It is also perhaps the first to bloom reliably in early Spring, a welcome sight in the barren landscape with its rosy-purple flowers profusely produced.
R. carolinianum is considered to be the most widely-used parent in creating lepidote hybrids, and justifiably so. It gave rise to very satisfactory offspring, usually quite hardy, especially when mated with an even hardier partner as, for example, was the case when the famous 'P.J.M.' was created. In my breeding programme both the pink and white forms of R. carolinianum were used. Crossed with R. lapponicum the two forms yielded hybrids with distinct differences, as expected. Both grexes are hardy, quite uniform in their clones and have merit. Another carolinianum cross, R. carolinianum X patulum, is in its best clone a low, well-formed bush with fairly large rounded dark green leaves, and at blooming time large open bells of a silvery pink scattered densely over them. It is as effective alone as it is in mass plantings, blooming well even in shade.
Good crosses of R. carolinianum were also obtained with RR. chryseum and impeditum. Unfortunately, many R. carolinianum hybrids are sterile, preventing the raising of second generation hybrids F2 seedlings.
Finally, a few lepidote hybrids which do not have a very hardy parentage should also be included in this presentation. Some of these are hardy in the Toronto area, some are only marginally so, but they have horticultural merit. 'Lavendula', a well-known Hobbie hybrid, is reputedly sterile, so it was somewhat of a surprise to find a well-formed ripe seedpod on one of the plants on an autumn day. It was harvested, the seed was sown, it germinated in due course and yielded some three dozen healthy plantlets. Two of the best seedlings were saved. One grew into a very dwarf plant with comparatively large, light pink open bells. The other has very large (60-70 mm) impressive flowers of a lavender or amethyst-violet colour. The former is hardy in Mississauga, the latter just about marginally so.
Then, a R. chameunum hybrid should not be forgotten. This species was crossed with a R. calostrotum hybrid ('Cutie'). All of the clones have interesting foliage and pink flowers with a large red flare, sitting on erect, long petioles. They are especially effective when the late afternoon sun strikes them.
In turning to the large-leaved rhododendrons, it may be said that R. brachycarpum, ssp. tigerstedtii played the same role in my breeding programme as did R. lapponicum in creating hardy lepidote hybrids. However, being much easier to work with, it was possible to obtain three times as many hybrids, about sixty, including a few second generation ones and F2 forms. As a rule, the hybrids are robust, vigorous and tall-growing plants with large leaves. There are, however, some notable exceptions when the other parent is a dwarf, like R. forrestii var. repens. All are, or were, leaf hardy so far in Mississauga. Only a few of the numerous crosses made can be briefly referred to here.
A cross with R. 'Mars' (the reverse cross was also made) yielded robust-growing plants, the tallest nearly 200 cm in twelve years, except one clone which is medium in height. All have light to medium-deep pink flowers, most with a reddish hue or streak. More than half of the clones were bud hardy after a severe winter when the temperature dropped as low as -31 C. A cross with R.. 'Pinnacle' gave similar results, though they flowered with a lighter shade of pink. R. 'Catalgla', in its cross displayed in all clones white flowers with a yellow flare. This hybrid could hypothetically be one of the hardiest elepidote crosses possible to make.
Crosses were also made with RR. 'Carmen' (one clone very dwarf flowers light red), Cerasinum (edge of flower light red, centre yellowish), 'Goldfort' (white), williamsianum (pink bud opening to white flower), arboreum, forrestii var. repens, orbiculare, metternichii 'Elizabeth', 'Treasure' and many others that have not yet flowered. My experiments with R. aureum as a hardy parent were neither encouraging nor successful. After fifteen years, only one hybrid displays sufficient resilience and good health, as well as a good habit, pleasant foliage and creamy white flowers. It is R. 'Catawbiense Album' x aureum. I had better results with R.. nikomontanum, which is a dwarf, quite hardy species (or established natural hybrid).
The next bet in creating hardy hybrids is, of course, the well-known and proven R. catawbiense, the type, and even more, its white and compact forms, as well as some of its excellent hybrids.
One of my earliest crosses, considered to be one of my best, is R. 'Ice Cube' x R. yakusimanum 'Exbury'. Buds in all clones are light pink (and not purple), opening to snow-white flowers. All are extremely floriferous, strong-growing, low to medium-high shrubs, with large, very dark green leaves. They require medium shade for best performance, with not more than one or two hours of mornng or late afternoon sunshine. Another similar cross, R. catawbiense var. compactum x yakusimanum 'Exbury', has produced more sun-tolerant plants. All clones have pink buds, opening to white or light pinkflowers on neatly rounded dwarf to medium-low bushes with pleasing foliage.
An early cross, R.. 'America' X 'Carmen' displays lovely clean dark red flowers of substance on neat, very dwarf bushes with pleasing vivid green foliage. It is, however, only marginally hardy in Mississauga.
It was thought that crossing R. 'Mrs. C. S. Sargent' with 'Janet Blair' should give hardy plants with attractive flowers, and indeed, so it happened. However, with a few exceptions, most of the clones do not root well. Another cross made with the same thought in mind, R..'Catalgla' X 'Treasure', more than fulfilled my expectations. The neat dwarf to medium-sized shrubs with rounded leaves have flowers ranging from red through all shades of pink to white. Of this grex 29 clones are under observation at present.
The compact form of R.. catawbiense gave hardy and quite satisfactory hybrids with R.R. williamsianum, orbiculare, wallichii and (R. brachycarpum X souliei). Several of the clones of the latter grex inherited the characteristic metallic-green foliage of R. sauliei.
For many years I have received samples of pollen from Dietrich Hobbie. One of these, R. wardii x yakusimanum, was crossed onto R. 'Catawbiense Album'. After thirteen years, several of the clones have not yet flowered, while others had flowers of no merit. However, one has very acceptable flowers of light yellow bells carried in loose trusses, good medium-green foliage, and an interesting tiered growth habit. It is hardy here, which unfortunately cannot be said of Hobbie's primary cross. It may be worthy of mention that the R. wardii used is a Volker selection. It does not have the red spot of the LST form, but is of a deeper yellow colour, as I understand.
R.. 'Sham's Juliet' X (yakusimanum X 'Mars') should not be by-passed. The best form has warm, deep reddish-pink flowers. R. 'Mars' x (yakusimanum X 'Mars') proved to be hardier than expected. In Mississauga it has bloomed during the past few years without damage and in profusion, with large trusses of glowing red flowers of an exciting shade.
In closing this communication, it might be of interest to note that reference has been made here to about 40 grexes, of which hardly more than 70 clones were briefly described. This compares to about 250 or more grexes, comprising well over 1500 clones altogether which are under observation at present, not counting seedlings in my nursery. The balance of the approximately 600 seed lots which germinated throughout the years were either abandoned for reasons of necessity, destroyed for lacking any particular merit over existingr hododendron hybrids, or lost. Some were donated to public gardens.
Finally, I would like to express my gratitude to Richard Birkett for his encouragement and help in so many ways. I am also greatly indebted to Richard for so splendidly introducing the hybrids I was fortunate enough to create, in a slide show at the 14th Annual Meetings of the Rhododendron Society of Canada. I consider this to be a great honour bestowed upon my rhododendron hybrids, as the slide presentation was somewhat the focal point of the meeting. In appreciation, I thought it might be fitting on that occasion to name one of my hybrids for the first time, after the greatest hybridizer of all times; the hybridizer to whom not only we interested in horticulture, but also our fruit-growing friends and all mankind can be thankful, for receiving so much for so little in exchange for enormous unparalleled work performed to our benefit. This great hybridizer is: the BEE. Therefore, the name of my first rhododendron, baptized at the meeting, is Rhododendron 'Abeille'. The original cross, which I made in 1971, was R. keleticum x dauricum (the deciduous type collected by Vasak in Siberia). R. 'Abeille' is an open-pollinated seedling and appears to be the best clone in the grex. I also thought that R. 'Abeille' should be the property of the Rhododendron Society of Canada.
Note: This paper is a somewhat condensed and modified version of a talk and slide show delivered by Richard Birkett at the 14th Annual Meeting of the Rhododendron Society of Canada at Halifax, in 1985.
Source: Bulletin of the Rhododendron Society of Canada. 1985, Volume 14 No.2, pp. 18 to 22.
Rhododendrons are a common sight in Edinburgh. Almost every garden seems to have a few, the woods are full of R. ponticum and some of the finest species and hybrids grow at the Botanical Gardens which are located several miles from where I used to live. It was hard to imagine a landscape without rhododendrons. That, however, was exactly what I found when I emigrated to Canada in 1968. In retrospect I should have headed west to Vancouver but, Toronto offered the best opportunities for work and I settled there. The prospect of long, hot Canadian summers and plenty of winter skiing seemed an attractive alternative to eastern Scotland's cold, damp summers and even colder, damper winters. Rhododendrons, I was told, did not do well in Ontario.
Certainly a few iron clads could be purchased from local nurseries and 'PJM' seemed to flourish, but there was not the wealth of colour and form which I was used to seeing. Some optimistic and, doubtless, wealthy growers tried importing plants from the west coast but invariably a tender rhododendron in Toronto is usually a dead rhododendron by spring. Just as I was convincing myself that marigolds and petunias were the plants for me, I was fortunate to meet Joe Brueckner and things, rhododendron wise at least, took a turn for the better.
Dr. Brueckner was born in the Austro-Hungarian monarchy and developed an interest in rhododendrons during his visits to the Alps. In the late 1940's Joe, with his wife Martha, left Hungary for Switzerland and, after two years, emigrated to New Zealand. Several years later they settled near Saint John, New Brunswick, in Canada, where, in spite of the proximity of the Atlantic Ocean, winters are bitterly cold.
During his stay in Switzerland, but more especially in New Zealand, Joe became very interested in rhododendrons. He was determined to grow them in New Brunswick but recognized that there was no information available on raising plants in such a hostile climate. Some of the local gardeners had tried a variety of English hybrids with remarkably consistent results. Every plant died. In spite of this Joe felt certain that rhododendrons could be grown successfully in the area for, after all, they are to be found in nature in the tropics and the arctic and many places in between.
The first approach involved the raising of plants from R.H.S. seed and, although some successes were achieved, the results were not altogether satisfactory. It was at this time that fate intervened. Among the inhabitants of Saint John, who were treated to visions of dead and suffering rhododendrons, was a local gas station attendant. He remembered regularly filling up a converted Volkswagen mini-bus which looked very much like a greenhouse on wheels, loaded to the brim with rhododendrons. As it turned out, the van belonged to one of Canada's premier rhododendron hybridizers, Captain Dick Steele. A meeting was arranged and before long Captain Steele had explained the fundamentals of his hybridization program and the methods he used to select crosses and grow on seedlings.
Armed with this new knowledge Dr.Brueckner, at age 56, began to make his first crosses utilizing 'Mars' and R. maximum. Nothing especially significant was achieved and subsequently none of the plants showed the degree of hardiness necessary to insure success in New Brunswick, however, it was a start. Rhododendron maxi-mum was soon abandoned as it yielded inferior hybrids which seemed to be happy only within certain restrictive growing conditions.
The following year crosses were made using 'Ice Cube' and the Exbury form of R. yakushimanum, which generated very interesting plants with definite cold tolerance. Subsequent observations have shown that the Exbury form imparts a much greater degree of cold hardiness to its off-spring than could be expected. Many other hybrids were tried but only 'Mrs. C. S. Sargent' was hardy.
The problem was, of course, where to start? Inquiries at the major nurseries yielded nothing of value. Arboretums were also of no help, in spite of the fact that collectors such as Rock, who explored in the Kansu region of northern China, had sent back seeds and plants of hardy species.
The first breakthrough came when Joe wrote to Dietrich Hobbie and discovered that he had visited the Great Slave Lake region of Canada's Arctic. It was there that an erect growing lapponicum had been located by him which, at a height of close to 20 inches was clearly not covered by snow at times during the winter months. Arrangements were made for plants to be collected and sent on to Saint John. The second interesting development came when Vladimir Vasak, a Czechoslovakian botanist, was contacted. Vasak had collected in various parts of the USSR and had obtained seed and plants of R. dauricum and R. aureum. One of the dauricums collected northwest of Lake Baikal was used in some of the crosses. Rhododendron ledebourii, which is probably just a local variant of R. dauricum var. sempervirens, was also collected by Vasak in the Altai Mountains at the Kadrin River, and promised to have great potential as far as contributions to hardiness and quality were concerned. It was some time before R. ledebourii could be used in the program as it took several years to grow on plants to flowering size from Vasak's seed. Possibilities for the production of cold tolerant lepidote hybrids were enhanced with the discovery of literature dealing with a hardy form of R. brachycarpum. During the Japanese occupation of Korea, seed of various trees and shrubs had been collected by the Japanese Department of Forestry. Dr. Tigerstedt, in Finland, had obtained seed of a particular form of R. brachycarpum which had been collected from the northern part of Korea and he observed that the resulting plants were hardy, tolerating -45 degrees Fahrenheit. Frequent attempts were made, by Joe, to locate Dr. Tigerstedt's R. brachycarpum or to obtain seed though none were successful. Fortunately it was discovered that Orlando Pride had managed to obtain seed of R. brachycarpum from Finland, possibly from Dr. Tigerstedt himself, and a small seedling was sent on to Dr. Brueckner. Shortly afterwards, Pride destroyed all his brachycarpums presumably because they didn't do as well as expected. At a later date Nitzelius described R. brachycarpum ssp. tigerstedtii, and quantities of seed, as well as pollen, were also obtained from him. The basic ingredients for a successful lepidote and elepidote hybridization program were now in place. Apart from those mentioned, a number of other hardy species and hybrids were also used. Innumerable crosses and attempts were made over the years resulting in some 800 seedlots, about 2/3 of which germinated.
R. lapponicum: In winter, temperatures in the Great Slave Lake area can drop to -70 degrees Fahrenheit. Desiccating arctic winds are common and, as a result, most plants seek refuge under snow. Although the average snowfall is in the region of 40 inches per year, the actual accumulation is significantly less. Typically, R. lapponicum grows to only several inches in height and is a prostrate, compact, branching shrub. At 20" in height, the form originally discovered by Hobbie, on the south-east side of Great Slave Lake, must spend a large part of the winter exposed to the elements and can thus be considered exceptionally hardy. The flowers are somewhat larger and redder in hue than the type and the leaves are slightly longer. Young shoots from around the base of the plant may grow 3 to 4" in one season with terminal shoots on older branches growing at a rate of between 1/2 - 1". Flowering, in New Brunswick, takes place in early May and by early summer seed capsules are well developed and the following year's flower buds are set.
With the onset of winter, the leaves completely dehydrate and can be rubbed to a powder between the fingers, making it seem as though the plant has died. This appearance continues even through mild spells in winter and usually well into spring at which time the leaves fill out and the plant resumes normal growth. It seems likely that this dehydration mechanism is the reason that the plants can survive the harsh conditions in their native habitat.
Pollen, first collected in 1969, was used to make a number of hybrids but only a few were successful as they were very difficult to cross. None of the original plants of the Great Slave Lake lapponicum have survived in Toronto due to the hot summers and relatively mild winters, however, some very interesting hybrids have been produced.
This species, or at least the type that Dr. Brueckner is working with, was not the easiest subject for breeding purposes. The flowers are frail and easily break off on emasculation. In addition, there is also scant production and supply of pollen. Of the hundreds of individual attempts which were made, only a few proved successful and, in the end, 19 hybrids were obtained. Few of these have an overall garden value as they prefer cool and moist summers. However, crosses with R. racemosum (named 'Nahanni'), R. calostrotum 'Gigha', R. carolinianum (interestingly the hybrids of the white form seem to be more resilient than those of the pink form) as well as R. chryseum, R. dauricum and 'Ptarmigan', where R. lapponicum was the seed parent, all have merit.
Both R. dauricum var. sempervirens and R. ledebourii are non-deciduous and grow to between 7 and 8 feet after 20 years. Flower colour is purple with a touch of pink, although R. ledebourii tends to be a little warmer. The original R. dauricum var. sempervirens was obtained from Moscow by David Leach, who gave it to Peter Cox, who gave it to Joe. It is a well behaved plant and is considered to be attractive all year, however; its most important contribution is its ability to pass on its cold hardiness to its off spring, but comparatively little of its morphological properties. The size and growth habit of the other parent, the foliage, the size and colour of the flowering come through in the hybrids to a marked extent. Because of their early flowering, R. dauricum var. sempervirens and R. ledebourii were mainly used as pollen parents in the hybridizing program. Both species performed equally well in Saint John and in Toronto. Deciduous dauricum (type) as well as several other forms, such as the white form from Hokkaido, were also used. Rhododendron dauricum proved vastly easier to work with than did R. lapponicum. As a rule, and with only a few exceptions such as R. dauricum var. sempervirens x R. moupinense, R. dauricum was the pollen parent since it is one of the earliest flowering rhododendrons. Of the numerous crosses selected for long term evaluation the following hybrids have proven to be most interesting. 'Azuray', a hybrid of R. augustinii x R. dauricum var. sempervirens, is a large, robust, very resilient and hardy bush. The flowers are similar to R. augustinii, in that they are large and open, however, the flower colour tends toward a light violet blue. The new shoots are distinctly yellow and provide an added dimension to the plant. 'Audacious' an open pollinated seedling of R. dauricum var. semper-virens is, after 12 years, 7-8 feet tall and just as wide. It is one of the first plants to bloom in the garden and the large lavender pink flowers stand up to full exposure to sun and are not affected by early frosts. In addition, it has bloomed every year without fail, even when 'P.J.M.' was nipped bv late frosts.
Rhododendron dauricum album crossed with R. fletcheranum has yielded a low to medium sized plant with lovely dense foliage which is attractive all year round. The buds, which are apricot pink, open to large white or creamy white flowers, suffused with pink in the initial stages.
Miscellaneous Lepidote Hybrids
'Fairy's Fairy' is the name for R. keiskei 'Yaku Fairy' crossed with a hardy form of R. keiskei. The shrub is a dense, flat, very low bush with deeper yellow flowers than those of R. keiskei 'Yaku Fairy'. In addition, the plant has come through many severe winters whereas R. keiskei 'Yaku Fairy' generally succumbs.
Rhododendron carolinianum album crossed with (R. chryseum x R. lutescens) is a low shrub with bright yellow, ball-shaped flowers. Both the white and pink forms of R. carolinianum have been crossed on to R. chryseum with good results, (R. chameunum x 'Cutie') yielded a nice plant with good pink flowers and a red flare.
Rhododendron aureum is mentioned here, not because of any successes achieved in growing either it or its hybrids, but because it failed dismally. Seed collected from the Baical Sea, Kamchatka and also from Japan produced plants which simply disappeared from the garden in Toronto. The only successful cross, out of the many that were tried, was R. catawbiense album x R. aureum. Further attempts were therefore abandoned in spite of the obvious contributions to hardiness which R. aureum could potentially make. Rhododendron x nikomontanum, a plant which is hardy in both New Brunswick (snow cover?) and Toronto, has proven to be a reasonable substitute, contributing both hardiness and compactness to its offspring. The original plant, obtained from Hobbie, is low growing, spreading out rather than up, and has a pale yellow flower with a greenish yellow blotch. Joe has some doubts as to whether or not this form is pure R. x nikomontanum, however, the flower does correspond as typical of the type according to descriptions by Japanese authorities.
R. brachycarpum ssp. tigerstedtii
Rhododendron brachycarpum ssp. tigerstedtii is known to be hardy to -45 degrees Fahrenheit and the original plant is now around 8 feet tall and 12 feet wide, after about 23 years from seed. Growth is initially very slow; however, this form eventually becomes a large, spreading bush, as wide as it is tall. Even in New Brunswick, it needs a fair amount of shade as the plant will tolerate very little sun. The flowers are white, relatively small and with a greenish blotch, not unattractive but certainly humble. The flowering period varies greatly depending on the weather, but R. brachycarpum ssp. tigerstedtii can be considered a medium bloomer. Certainly one of its great attractions is the foliage and in a wet year leaves are produced which are noticeably longer than those formed in a dry year. They are also very sensitive to weather conditions and will curl up, on a cool night, long before any of the other species.
From a large number of crosses over 60 hybrids were obtained, including a few F2, second generation crosses. Of all the partners with which this rhododendron has been paired, the following have proven to be the most promising.
Species: R. catawbiense album, R. catawbiense album 'Catalgla', R. cerasinum, R. williamsianum, R. forestii var. repens, R. smirnowii and R. arboreum.
Hybrids: 'Janet Blair', 'Mars', 'Pinnacle', 'Rodhatte', 'Elizabeth'.
Crosses with 'America' and 'Nova Zembla' led to vigorously growing, robust plants which were rejected, as flower quality, in the first generation at least, was poor.
All of the R. brachycarpum ssp. tigerstedtii crosses have proven to be leaf hardy in Mississauga and, with one or two exceptions, bud hardy. Most notable of the exceptions are crosses which involve 'Elizabeth' but even here second generation hybrids have shown a few hardy clones. The R. arboreum hybrids, from crosses made in 1978, have yet to flower.
Only R. catawbiense album 'Catalgla' x R. brachycarpum ssp. tigerstedtii has been exposed to temperatures as low as -35 degrees Fahrenheit. While the plant flowered without any bud or leaf damage it should be noted that it has not been subjected to any long term testing.
R. yakushimanum, Exbury form Rhododendron yakushimanum, has been established as a parent which lends hardiness to its offspring beyond expectations. A cross made in 1969 with 'Ice Cube' yielded a number of very satisfactory clones. Those that have been named are 'Albula', which has large ball shaped trusses, 'Igloo', which is a rounded bush always covered in flowers, and an as yet unnamed clone with spotless white flowers. All open from pink buds and have dark green leaves which are retained for 4 or 5 years. The clones are generally more vigorous than R. yakushimanum and 'Albula' is now 5 feet tall and 6 feet wide after 20 years, while 'Igloo' is 6 feet tall and 6 feet wide. This particular cross is a good example of the contribution which R. yakushimanum, Exbury form, makes towards in-creased hardiness. All the clones are sensitive to sun and should be grown in full to light shade where they will put on an impressive display of bloom every year. A number of interesting hybrids resulted when (R. yakushimanum x 'Mars') was crossed back to 'Mars'. All have red coloured flowers, some with most unusual tints. The names for two of these clones are 'Hot Dawn' and 'Ma Chere'. It is interesting to note that while 'Mars' is hopelessly tender in the Toronto area, all of these clones have flowered every year with absolutely no damage.
R. catawbiense compactum and miscellaneous hybrids When R. catawbiense compactum was crossed with R. yakushimanum, Exbury form, clones were produced which gave very hardy, well rounded bushes with good foliage. With two exceptions the flowers open from pink buds and then turn white. Not as hardy, but with a pleasant light yellow colour, are clones of (R. faurei x 'Inamorata') x (R. wardii x R. brachycarpum). They started flowering several years ago and have done so every year since, without damage. The same may be said of 'Lionel's Red Shield', a hybrid originating from a cross of America' x 'Carmen'. Ten-year-old plants are about 1 foot high and 3 feet wide with vivid clean red bell shaped flowers.
Summing up, the Brueckner garden is located in Mississauga which lies at the southern periphery of the greater Toronto area. It has noticeably milder winters than communities bordering Toronto to the north. Even so, since the time that Joe began the garden, temperatures as low as -25 degrees Fahrenheit, (in 1981) have been experienced. Last winter was relatively mild with a minimum of -9 degrees Fahrenheit, although there was no snow on the ground until well into March.
Testing for hardiness involves so many variables that it is hard to state categorically that a plant will survive, anywhere in the country, down to a certain temperature. Nevertheless, it is possible by comparing how existing varieties do, to say that a plant is better. There is no question in my mind that Joe has hybridized some superb, hardy plants, which offer gardeners in Eastern Canada, and elsewhere, an opportunity to grow rhododendrons just like 'back home'.
The author: Barrie Porteous, a member of the American Rhododendron Society, served as editor of the Bulletin of the Rhododendron Society of Canada from 1984 through 1989.
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