JARS v57n4 - Let's Talk Hybridizing: The Saga of the Parks' Rhododendrons

Let's Talk Hybridizing: The Saga of the Parks' Rhododendrons
Joe B. Parks
Dover, New Hampshire

Reprinted from The Rosebay, Vol. 30, No. 2, Fall 2002/Winter 2003.

This is a saga of a quest for superior rhododendrons for cold climates - not rhododendrons that would merely survive and flower in upper New England but ones that you would really crave for your garden. Although I had been hybridizing rhododendrons - "playing" is more accurate - since the early 1950s, I was ill prepared, rhododendron-wise, for New Hampshire when coming here from Virginia over a quarter century ago.
It soon became obvious that in spite of much advice and literature to the contrary, many of the loveliest rhododendrons just weren't up to New Hampshire's erratic winters. Winters sometimes without snow cover, winters frequently in the –18°F to –23°F range and sometimes lower, day after day with temperatures not getting above zero (F) and winters with erratic warm periods in the +40's to +50's seemingly always followed by the coldest weather of the year! There were of course the "Ironclads" but many are pastels, have poor plant habit and some, in spite of their reputation, poorly adapted to the vagaries of New England's climate. Although there were many esteemed New England hybridizers such as Ed Mezitt producing hardy hybrids, it was concluded that it would be fun to try to develop my own that might be better adapted to upper New England's capricious climate.
Over the years, I've made hundreds of crosses and raised myriads of seedlings. Out of these have come a few superior, hardy plants apparently worth naming. Time of course may alter this judgment. It is unfortunate that early on I didn't appreciate the importance of specifically developing elepidotes with disease and insect resistance as I did with the Cherokee Azalea Series. As the availability of insecticides and fungicides becomes more and more restricted, this will become of much importance to those who love these wonderful plants. As I approach the age of 88, development and testing time being what it is, the likelihood of making a contribution in this regard is on the low side. However, approached seriously and using modern techniques, there is no reason not to have a substantial number of disease and insect resistant hybrids available within the reasonable future. It is important that someone pickup the baton and move forward on this.

A Bit of Hybridizing Philosophy and Advice
Of all the pleasures of working with plants, clearly the greatest is that of creating a new plant that has never existed before. In more exalted moments, I like to think of myself as a hybridizer when, in fact, I really am just a guy having a lot of fun. True, there is a plan and it is followed methodically with study, research and objectives. And true, in the last 50 years some plants (perennials as well as rhododendrons) have been developed that some say are an improvement - but in the end, if it weren't so enjoyable, I would most likely be doing something else.
Before we get mired in the details, let me give you a few reasons that make hybridizing so enjoyable:
First, every cross brings forth a plant - whether worthless or useful - that never existed before. Someone has said it's almost like playing God; I'm not so sure about that, but most certainly it's your call that counts. Your garden is your laboratory, ready to use whenever you wish.
Second, your imagination is the only limitation as to what can be achieved! Just remember, the most beautiful rhododendron of all is still out there waiting in the wings for you to release it with a bit of pollen. The princess that turned a frog into a prince with a kiss has nothing on you.
Third, the pleasure/time ratio is very high. Once you have started the process, the plant does most of the work and you can go about your other business while it is "working" i.e., doing what comes naturally. If you have a plan, you can be successful with a modicum of effort.
Fourth, the pleasures of achievement never stop. Each step in the process is a cause for celebration. You pollinate and, glory be, seeds are produced; the seeds are planted and a crop, the rarest of the rare - your own hybrids - appear; you set them out and when they finally come to flower you'll never know if canons boom and bells ring for you'll be far out on Cloud 9.
Objectives are most important in a hybridizing program but it can't be said that I started down the road with any particular shrewdness; I wanted more azaleas (this was in the early 1950s) but they were too expensive. Ergo, grow them from seed. It became obvious rather quickly that it was not possible to just stumble around in the dark and hope something good would happen; that if there was any hope for "nice" plants then some homework had to be done. The old saw that goes "If you don't know where you're going, it doesn't make any difference how you get there" was still in force.
Plants with better flower quality and color were the only objective at first. Some deciduous azaleas from those early crosses are still around fifty years later - gorgeous, fragrant flowers, but who would want the gawky, mildew prone, insect chewed plants under them. When I retired the second time (that one didn't "take" either) and moved here, new vistas opened with a plan to develop new rhododendrons. The major objective was hardier plants; but to be acceptable they had to have either very dark or very light flowers, i.e. no "muddy" tones and bushy with (hopefully) dark, glossy leaves and an extended flowering season. Had I realized at the time how difficult these objectives were and how long it would take, some perennial with a shorter turnaround, such as daylilies, might have been chosen. So, not realizing the difficulties, I just bulled ahead blissfully unaware of the fustrations to come.
Since the "Ironclads" already existed, it seemed wise to use them as a parent. Had it been known just how poor and unreliable some of them are, different parents would likely have been chosen. But I didn't know any better and some great plants have resulted. This is the great advantage of being an amateur; you don't know that "It won't work, it can't be done!" so you go ahead and accomplish something the experts "know" to be impossible.
My approach was very simple, perhaps even simplistic, cross "Ironclads" with more desirable, but tender (New Hampshire-wise) plants. Early on, many "Ironclads" including 'America', 'Nova Zembla', 'Roseum Elegans', 'Ice Cube', etc., were planted. Other hardy plants were obtained from cold climate hybridizers such as Pride and Shamarello. In addition, many other plants were obtained for testing, particularly those Dexter Rhododendron fortunei hybrids reputed to be hardier than most. Pollen was collected from everywhere - even at truss shows. I am never without a desiccant bottle and capsules and have gradually built up a very substantial pollen bank.
It was soon obvious that hardiness ratings of existing rhododendrons were, too often, more imaginative than real. So, in the early 1980s, a hardiness survey of New England rhododendrons was initiated. Over a period of some fifteen years, with the help of many ARS chapter members, thousands of entries on hundreds of plants growing in Massachusetts, New Hampshire and Vermont were compiled. This data has proven useful in evaluating the hardiness of plants used in hybridizing. In this regard, it is clear that climate type, day length, cumulative temperatures and season length are equally important in hardiness determination as either of the commonly used measures: winter minimum temperatures or the range of winter temperatures.
Very early in the game, it was learned from other hybridizers, that to increase color range, it was necessary to use parents with the darkest flower colors possible. As Weldon Delp pointed out at a Canadian Hybridizers Round Table, "Go for the dark colors, the pastels will take care of themselves." Unfortunately, there is little information as to what characteristics will actually prove dominant when a cross is made. Will progeny be tender or hardy, will they likely have dark flowers given only one dark parent, will plants be compact or leggy, etc.? So, much hybridizing has been a real crapshoot based mostly on faith rather than expertise or science.
I still know very little. In fact, the more I learn the more certain it is that I really know very little about what will succeed. But there are a few things that have been learned that can usually be counted on when making rhododendron crosses, things, that had they been known early on, would have probably saved considerable frustration. Here are some (for whatever they are worth):
-'Roseum Elegans' delivers hardy children but its genes seem to dominate more often than not,
-'America' tends to have leggy children but does a good job of transmitting its red color,
- 'Henry's Red' produces mostly raspberry pinks and reds (though crossed with the right plant it might produce a stunning hardy, dark purple),
- R. hyperythrum delivers compact, heavily branched plants with most everything it is crossed with,
- R. fortunei hybrids produce hardier progeny than might be thought,
- R. fortunei hybrid progeny are often more fragrant than parents several generations previous,
- Plants with some fortunei in their make-up tend to have glossy leaves.
- If a particular characteristic is desired in the progeny, it appears more likely to be achieved if it exists in the female parent - this is controversial but seems to be the case in my experience.
- Seedlings can be pushed into flowering within 2½ to 3 years or less by providing year-round light (14 hours) and heat (around 60°F).
- If you want dark flowered progeny with any certainty, both parents must be dark flowered; i.e., red x red = red; red x purple = red or purple; purple x purple = purple or red, etc. However, there will be muddy colors, whatever the parentage.
- If two plants prove incompatible, i.e., pollen from the selected male plant will not fertilize the female plant, then the sterile pollen technique, a four-step process, should be used. The steps are:
1) collect pollen from the female plant,
2) sterilize this female pollen (175°F for 15 minutes or treat it with high proof alcohol, filter and dry it),
3) place this sterile female pollen on the female stigma, and
4) then place the male pollen on the female stigma. This has proven successful in many plant breeding programs.
- If a R. degronianum ssp. yakushimanum hybrid seedling has leaf indumentum, the flowers will do the "yak dance", i.e., fade no matter how dark they are in bud.

Naming New Hybrids
With thousands of rhododendrons out there, unique plant names are quite difficult to devise. So I have chosen a technique that simplifies the problem; either use a person's name (nearly always unique) or use a unique first word in the name. For elepidote rhododendrons, "Cocheco," the Indian name of a local river; thus 'Cocheco Belle'*, 'Cocheco Elf', etc., is used; for deciduous azaleas, "Cherokee" (my heritage) is used; for evergreen azaleas, "Piscataqua," the Indian name for another of our rivers, was chosen; and for all other plant hybrids such as perennials, shrubs, etc., "Parkwood" is used.

R. 'Kathryn Forbes'
'Kathryn Forbes'
Photo by Joe B. Parks

The Parks' Hybrids and How They Were Developed
Since everyone was saying how hardy 'Scintillation' was, early on I had high hopes for it as a parent. However, these high hopes were later dashed when it proved to be not reliably bud hardy below about –13°F - a warm winter for Dover. But in 1983, thinking it hardy, it was crossed with 'Roseum Elegans'. Out of this cross, a few plants proved hardy and one seedling proved better than either parent.
'Anne Goss' (named after my oldest daughter; cover photo) is a superior plant in every way. At twenty years, it is a compact plant about 8 feet tall by 15 feet across with glossy dark green leaves. It looks good in the landscape, is attractive throughout the year, is a heavy bloomer and is bud hardy to at least –20°F. Its flowers (a bit lighter than 'Scintillation') surrounding dark pink buds make a beautiful truss.
'Roseum Elegans' as the seed parent has produced some good purples. Crosses with 'Lee's Dark Purple' and 'Dexter's Purple' didn't prove useful but crossing it with 'Olin O. Dobbs' proved to be a different story. Reputedly leggy and not too reliable here, it does not sound like the best of choices but since that was the only pollen from a dark purple flowering plant available, it was used anyway. This cross produced two plants with dark purple flowers, two medium purples with heavy, dark blotches and a number of lavender-pinks with brown blotches. Though perhaps not quite as compact as might be desired, the plants are well leafed and a distinct improvement over both parents. Four of these offspring have been named:
- 'Florence Parks'* is a heavy flowering dark purple. The flowers are set off well by the dark green leaves. Leggy at first, it has filled in very nicely over the years and is a very desirable plant.
- 'Cocheco Purple Passion' flowers are a rich, very dark purple (the darkest I've seen) with a tightly packed ball truss (20 or more flowers) set closely in a rosette of dark green leaves like an oversize boutonniere. The plant blooms heavily only in alternate years but is well worth the wait.
- 'Cocheco Purple Sentinel'* is a large flowered medium purple with a dark purple, almost black, flare centered in the top petal. The leaves are a medium green. In bloom, it is a very striking plant though not a tight as the previous two.

R. 'Purple Sentinel'*
'Cocheco Purple Sentinel'
Photo by Joe B. Parks

- 'Cocheco Butterfly'* is medium lavender with a brown flare that almost covers the top petal. It flowers heavily with fairly large trusses making it a lovely plant in the landscape.
'Roseum Elegans' crossed with itself produced mostly junk (flowers that never open, etc.) but also produced three plants that are a considerable improvement over their parent. In twenty-one years, none of these selfed hybrids have displayed the unfortunate winter desiccation (winter-kill) propensity of 'Roseum Elegans' - nor have their flower buds frozen. Better still, they all seem to root as easily as 'Roseum Elegans'. One has been tentatively named: 'Cocheco Roselegans'* is a heavy bloomer and has dark pink/lavender flowers. Leaf color and plant habit are quite similar to the parent but because of the good flower color and resistance to "winter kill" it is much superior. Its two sister plants have better flowers but so far their plant habit is not quite as good so are still being watched.
'Mrs Charles S. Sargent' has proven to be an excellent parent that produces compact, hardy offspring that typically are late flowering as she is. A cross with 'Dexter's Purple' in 1984 produced two plants well worth naming:
-'Kathryn Forbes' (named after my other daughter) is, at 19 years, a compact plant (about 7' x 10') with glossy, green leaves. It blooms heavily with, almost fluorescent, pinkish-purple flowers.
-'Cocheco Big George'* is a very large, fairly open (but not leggy), plant that has now reached over 12 feet tall by 15 wide. The glossy, dark green leaves are much larger than is common—some 9 to 11 inches long. These have won "Largest in Show" several times at the Massachusetts Chapter fall foliage show. It is a heavy bloomer with large, slightly ruffled pink flowers.
'Mrs Charles S. Sargent' crossed with 'Consolini P148'* produced one of the best pink flowered plants I've had the pleasure of growing:
'Cocheco Belle'*, after eighteen years, at about 8 feet, it is as wide as it is tall - almost a globe—covered uniformly with glossy, dark green leaves. In late May it is covered with large trusses of rose pink flowers - would that they were darker, but the perfect plant doesn't exist. It is similar to 'Bravo!' though an observer might agree that 'Cocheco Belle' is superior. But, far more importantly, 'Cocheco Belle' is more bud hardy - by at least 5°F - so for upper New England it is clearly the better choice.
- This cross also produced another lovely plant that remains un-named. It flowers heavily with quite large rose pink flowers. It has reached about 10 feet high by 15 across and is quite nice year-round in the landscape with its dark green leaves. Why hasn't it been named? Because there is already an over-abundance of pink flowered rhododendrons.

R. 'Cocheco Prince Royal'
'Cocheco Prince Royal'
Photo by Joe B. Parks

'Ice Cube' attracted attention as a potential parent early on because of its hardiness. Flower color, a pale sort of indecisive lavender, is a big negative but its hardiness makes it worth using. Out of several crosses with it as the seed parent, one in 1987 with an unidentified Dexter seedling, produced two nice hardy plants:
- 'Cocheco Peaches 'n' Cream', even though growing in almost full shade, has grown into a solid plant about 6 feet by 6 feet in sixteen years. The delightful flowers are light pink towards the edges blending to cream towards the center. Though it may be the heavy shade or the poor rocky clay soil where it's growing, this plant has not proven a heavy bloomer.
- 'Cocheco Honey Glacé'* growing in even heavier shade is also a solid 6-foot by 6-foot plant. The flowers are a light honey color. Heavy shade may account for the fact that it sets only a moderate number of buds. Now that there are rooted cuttings, both plants can be tested in better locations.
'America' would seem to be the perfect parent for New Hampshire hardy hybrids. It is very hardy - flowers even after temperatures in the minus twenties (F) - and blooms heavily with bright red flowers. Unfortunately, the bush is quite leggy, is floppy and has a poor leaf cover, so it is not the most desirable plant in the landscape. Worse, it tends to transmit its leggy habit to its offspring. Nevertheless, its hardiness and red color make it of value. One cross in 1983 with 'Dexter's Appleblossom' has produced several nice plants worth naming:
- 'Cocheco Double Ace'* has large flowers of a truly lovely shade of red, a tremendous improvement over 'America'. Though the flowers are not male sterile, stamens in some flowers tend to be petaloid, some having up to fourteen extra petals. This plant is in a poor, wet location, so it has had phytophthera problems - but has survived. Thus, I don't know whether it is genetically leggy or leggy because of "die-back." Again, cuttings growing in better locations will prove the plant's quality.
- 'Cocheco Bright Star'* flowers are a bit larger and perhaps an even brighter shade of red than 'Cocheco Double Ace'. Each petal has a lighter center (almost a stripe) that extends from the tip to the bottom giving a lovely star effect, thus the name. This plant is growing next to its sister and has the same problems. Both are being propagated and tested in a different situation.
- Unnamed, growing back in the brush was "lost" until it decided to put on a real show this year.
Tony Shamarello hybridized a number of excellent, hardy plants at his nursery near Cleveland, Ohio. Unfortunately, now that Tony has passed on, many have fallen into disuse. I have two of his hybrids, 'Sham's Candy' and 'Sham's Pink'. Both have proven to be top performers - and in some lousy locations too - even after the coldest of winters. Crosses of 'Sham's Candy' with 'Dexter's Appleblossom' and with 'Consolini P148'* produced two very nice plants. I consider the selection from the Consolini cross, yet to be named, to be among my finest hybrids:
-'Moira Forbes'* (from the 'Dexter's Appleblossom' cross) is a low growing, somewhat loose, spreading plant - after nineteen years it is about 5 feet high and 9 feet wide. The ruffled flowers are of a two-tone pink, with the petal edges being darker than the center. It is a heavy bloomer.
- 'Cocheco P8304'* (from the Consolini cross) will probably be named "Laura W." This is a heavy flowering, heavily branched, somewhat open plant reaching about 7 feet high by 10 feet wide in twenty years. The plant, growing under white pines, is definitely leaning towards the light so it would probably be denser with more sun. The large, ruffled flowers are difficult to describe being a pleasing two-tone pink set off by a tan flare in the upper petal.

R. 'Amethyst Ice'
'Amethyst Ice'
Photo by Joe B. Parks

My first rhododendron worth naming, 'Amethyst Ice', has proved itself over the years to be an excellent, hardy New Hampshire performer so I decided to try using it as a parent. The negatives to using it as a parent are that the flowers are quite pale in color and that it is a fast grower thus making for a large plant. But it flowers heavily, is nicely fragrant, and has a dense, heavy cover of dark, glossy leaves. So, I decided to cross it with a white Dexter (un-named) - both parents having R. fortunei in their background. Out of this cross came two unusual plants only one of which has been registered:
- 'Cocheco Sweet Perfume' is a compact plant, being under 5 feet high and about 7 feet wide after eighteen years. Growing in almost full sun, it is quite compact. The flowers are almost white, male sterile and mostly female sterile - though last year, with 'America' as the male parent, it produced a goodly volume of seed. There is an advantage to sterility; the flowers last much longer than most because, being unable to accept pollen, they are forever waiting to accomplish their mission. 'Cocheco Sweet Perfume' with its pale, almost white color would probably be just another cross that didn't make it were it not for its outstanding fragrance. In fact, the lily-like fragrance is so intense that, on a warm spring day, its delicious aroma is wafted though the garden.
- 'Cocheco Pink 'n' Sweet'* is a sister plant to 'Cocheco Sweet Perfume'. Its pale pink flowers open a week or so earlier. Although given a name for record purposes, it will probably not be registered as it is not quite as fragrant as its sister.
Although 'Boule de Neige' is not as "iron hardy" as usually cited, it's a compact plant that looks good year-round so it has been used it in a number of crosses both as the female and the male parent. One of the better crosses, using it as the seed parent, was in 1990 with 'Henry's Red'. All of the progeny have nice flowers of uncommon raspberry red shades but most are leggy. One has been named:
- 'Cocheco Raspberry Swirl' is a compact plant being about 7 feet tall and about as wide at thirteen years. Even growing in the shade, it has filled in nicely as it has matured. The ruffled flowers are a two-tone luscious color like red raspberries at their ripest.
Back in the early days when the Massachusetts Chapter met at a Wellesley church, we always had a fall plant exchange - bring a plant and choose a plant. In 1982, not having brought much, I waited till others had chosen and ended up with a flat of year old seedlings no one else wanted. Who brought them, I never learned. They were a complex cross of (ssp. yakushimanum x haematodes ) x (ssp. yakushimanum x ?), the "?" being because I lost the label and didn't remember the cross. Those hundred or so seedlings grew into quite a mélange most of which have been destroyed, but three produced low growing plants with good red buds, although they quickly do the "yak dance" and fade to an off-color pinkish-white. One of these three is an excellent plant: dark green leaves, indumentum, low compact growth (3 feet high by 10 wide in 20+ years) - everything but flowers that hold their color. A cross with 'Boule de Neige' in 1985 has produced several nice plants and several other crosses have produced compact seedlings:
- 'Cocheco Elf' is a dwarf growing plant under 30 inches high by perhaps 5 feet across after eighteen years. The dark green leaves tightly cover the plant. When in bloom, the lovely pale pink flowers hold their color well and cover the plant, often virtually hiding the leaves. This is a superior year-round plant for limited space.
- 'Cocheco Red Imp'* is also a hardy, very tight, compact plant that has grown to about 4 feet by 4 feet - a bit taller than 'Cocheco Elf'. The leaves are darker than but similar to 'Boule de Neige' and, like its sister, solidly cover the plant. The red, almost tubular flowers retain their color well. It is also an excellent plant for limited spaces.

R. 'Cocheco Red Imp'
'Cocheco Red Imp'
Photo by Joe B. Parks

Other Hybrids in the Wings
'Roseum Elegans' crossed with 'Henry's Red' (P9105) has not yet flowered. The hybrids should be hardy and offer the chance of some good flower colors. So far, however, the plants are a bit leggy and gawky looking so, like so many other crosses, nothing useful may result - only time will tell.
Crosses of 'Mrs Charles S. Sargent' with 'Melanie Shaw' (P9507) and with 'Doctor H. C. Dresselhuys' (P9505) have not yet flowered but have produced some nice compact, dark leaved plants. Time will tell whether they are desirable or not. It is the pleasure of anticipation and the delightful surprises that occur (though sometimes it's frustrations instead) that make hybridizing such a delightful occupation.
'Joseph's Technicolor Coat'* offered up unusual flowers in three colors for the first time this past spring. The flowers nestle tightly in the leaves and whether this is just an idiosyncrasy of the first flowering or a treasure for all time, we'll have to wait to find out. And too, at this point the plant is not particularly prepossessing. Unfortunately, it is also a good demonstration of why not to allow anyone else to help with your new plants. When it was moved from the raised bed to the propagation bed, the wrong label was moved, so it now has to be carried in the inventory as "cross unknown."
Crosses of R. hyperythrum with 'Boule de Neige' and 'Henry's Red' have proven very compact, mostly low growing and are, hopefully, hardy. One plant out of the 1995 'Boule de Neige' cross has flowered and is being named:
- 'Cocheco Pink Elf'* is heavily branched and, at 8 years, is only about 13 inches high by 30 inches wide. Leaves are a dark glossy green and the first flowers a medium pink.

R. 'Cocheco Pink Elf'
'Cocheco Pink Elf'
Photo by Joe B. Parks

Several of the 'Henry's Red' crosses are very heavily branched. All have dark green leaves with some being glossy and wavy. Dark flowers are unlikely but if the plants prove to be as compact as they promise there should be several choice hybrids out of the lot. Though only two years old (and "pushing" dwarf plants may distort them) one or two are being pushed into flower in an accelerated green house program.
Rhododendron brachycarpum ssp. fauriei is plant hardy here but not quite bud hardy - years go by without flowers. However, being quite compact and late flowering, it has considerable to offer as a parent. So, when it does flower after an early (and winter long snow cover), it has been used to cross with hardy, late flowering plants such as 'Henry's Red', 'America', 'Summer Rose' and 'Edith Pride' hoping to achieve June flowering, low-growing plants. Except for the 'America' cross, seedlings have already proven as compact and even more heavily branched than the hyperythrum crosses and also have darker green leaves. The flowers will likely be pastels, but if they flower late and continue their tight, compact habit there should be plenty of winners.
'Florence Parks'* crossed with 'Dexter's Purple' has so far produced one plant that has flowered. The plant itself is too young to determine its quality, but the large flowers are delightfully ruffled with a dark lavender edge and a pale lavender center. It is tentatively named 'Cocheco Lavender Lady.'*
This is not a complete rundown of all my named rhododendron hybrids, let alone the un-named, nor have the azalea or perennial hybrids even been mentioned. However, hopefully it will give the reader a feel for what is being attempted here and will provide some modicum of information to those interested in hybridizing.
All in all, it is a most delightful, enjoyable avocation. Try it and you'll never look back!

* An asterisk indicates unregistered name.

Joe Parks is Past President of the Massachusetts Chapter.