JARS v58n2 - Let's Talk Hybridizing: Starting Over

Let's Talk Hybridizing: Starting Over
Dennis Mac Mullan
Hamburg, Pennsylvania

I have been growing rhododendrons for over thirty-eight years, first in Greenwich, Connecticut, then on the north shore of Long Island. Currently I live in Hamburg, Pennsylvania. In the early days, like some of you, I was fascinated by yellow and orange flowers. I had never realized such plants existed in the rhododendron world. I then discovered that these plants did not just "spring up" in commercial nurseries. People had worked to develop them - adding this, subtracting that. They were hybridizing.
It got me thinking. Could I do that? I decided to at least give it a try. And that, my friends, was the end of me as a normal person. I became a plant addict of the worst kind - a rhody hybridizer. I blush to admit it, but it's true. After a period of time my wife, Leslie, a lovely and tolerant woman, decided there was little she herself could do to cure me. She thought perhaps that she could "check me in" for a few weeks at something like the Betty Ford clinic for rhody abuse. No such luck. She has learned what many spouses have - live with it! Now she just smiles and asks if I would like some help transplanting inch seedlings from one flat to another.
In those early days I looked at slides, studied photographs, read articles and books. I delved into every source I could find to unlock the doors to success. My interest was in developing really hardy plants with yellow, orange or true red flowers (without any blue undertones).
Conversations with "those in the know" turned out to be the most valuable sources of information. I learned more practical information from Carl Phetteplace, Jack Rosenthal, Bob Bovee and Jim Caperci than all the other areas of research. One of the most valuable pieces of information given was when I asked Carl Phetteplace how I could shortcut some of the usually employed trial and error methods and whether he could give me some tips - some rules of hybridizing. He answered, "There are no rules, just indications."
I am now 70 years old. Like many of you, I wish I knew then what I know now - about a great many things, but especially about hybridizing for rhodies that are suitable in my area - the interior Northeast. ¹ By "suitable" I mean something more than borderline cold hardy. For the sake of this article I would like to add a new word to the descriptive rhody lexicon: tough - as in a really tough but beautiful plant. A tough plant is hardy to 25F to 30F (-30C to 34C), is wind and heat resistant (or at least tolerant), and has a good truss, compact plant habit and acceptable foliage. It is also not susceptible to dieback as are many currently growing in our area. In each color group the ideal plant would be the winner of Best Elepidote Hybrid at the Helsinki, Finland, annual rhododendron show, assuming there is one! I can already see your heads shaking in disbelief!
Few really tough rhodies of good color have been developed because there is a "poverty of expectations" ² - a tendency to confuse the unfamiliar with the improbable. What we have not considered seriously seems strange to us; what seems strange is thought improbable; and what is improbable need not be considered seriously. In the mind's eye it is only a hop and a skip from "improbable" to "impossible." Jim Barlup, the Northwest hybridizer, has said that his least favorite word is "can't."
Well, I believe it is possible and that the "tough" rhodies are more than a dream. So why not give it a try? Let's start over. If the task seems overwhelming, share the work with friends.

A Basic: Get Organized
Get organized. Set your goals and develop a plan. Take notes. Use a looseleaf notebook and record each step you take. ³ I include dates. This project will take time, and it is important to know where you are, where you have been and where you are going. Take photos of your choice seedlings. Be certain they are honest photos of the blooms, not artistic masterpieces. They are for your use when comparing them in development and not impressing your friends. File the photos or slides. Don't leave things to memory. Naturally you must keep the record of yellow, orange and red separate (if you are interested in all three color areas).

Seedlings
The F ₁ -generation (yes, we are talking in terms of generations here) will probably not show you much for three or four years. When you find plants with hoped for traits (genetic bi-products) you can continue to test them while using some additional crosses. Label each seedling you decide to keep and destroy the rest. Be ruthless. Even if you have limitless acres to use, you still have to take time to care for these young plants. Don't waste your time! A plan such as this - well organized and executed - is like paying off your mortgage. It gets better every year. Keep abreast of the efforts of others who may be working along similar lines. Share information with them. Do not let people discourage you .
Definitely read the two articles by John Weagle of Nova Scotia in the Winter 2001 and Spring 2001 issues of our journal. They are filled with useful information on cold hardiness. His aims are different since he is working to develop dwarf plants that will thrive in the maritime climate of his area. Many other hybrids (and the plants with which he is working) are not suitable for the interior Northeast, but some of them are. I hope that some of these fine plants will eventually find their way to the United States.

Indications that Warrant Consideration
Contrary to some opinions, it does make a difference whether rhododendron A is the seed parent or rhododendron B. The genes of the seed parent are dominant in a large majority of rhody crosses. One excellent example is Mike Stewart's 'Carmen' x R. degronianum ssp. yakushimanum . The plant opens with rich scarlet buds, blooming to the same color and maintaining the color throughout its blooming period. The same cross, made a number of times with the yak as the seed parent, resulted in the usual "yak as seed parent," with flowers in the usual pink and fading to either pale pink or white, which we all know too well. Whatever traits (genes) are most important to you should be looked for in the seed parent. As the professional gambler will tell you, always look for an edge.
There is also the factor of "hybrid hardiness" to consider. Often a hybrid's "whole" will contain traits - hardiness among them - that exceed expectations based upon the components. For example:

Plant A	x	Plant B	= Plant C
Hardy to 10F	x	Hardy to 0F	Hardy to ?

Arithmetically the logical answer should be 5F (-21C) (or at least the very largest percent of the resultant seedlings). Not necessarily. Many will be hardy to 10F (-23C) (remember the seed parent dominance) and you will pick up some hoped for traits from the pollen parent (Plant B). This, of course, is dependent on the complexity and background (genes) involved in the composition of each parent. In the simplest form, with two species involved in the cross, the chance of this happening is lessened (and the results more predictable) because of the very limited variance in the genetic pool. (See discussion of 'Fashion Plate'* later in this article.

Plant Habit and Genetic Traits
Both good and bad plant habit and genetic traits are passed on to a plant's progeny. These must be factored in when choosing which plants to include not only in a specific cross but also in your entire program. Here is an example:

'Hotei'
Positive Traits	Negative Traits
-deep yellow color	-tender (0F), maybe 5F
-opaque (if desired)	-cannot take heat or afternoon sun
-attractive foliage	-slow to set buds
	-very prone to root-rot

Many of these negatives can be minimized in future generations of hybrids. The question you must address is your willingness to include the negative genes in order to gain access to the positives. Bearing this in mind, the following are examples of plants I would avoid and why:
R hododendron fortunei (including Gable's hardy form used by Don Hardgrove and many other Eastern hybridizers) is an old favorite (hardiness, large flowers, fragrance) but with what I feel is a major flaw: lengthy pedicels resulting in partially hanging trusses. This gives the impression of "incompleteness." Too often it seems as if one or two more flowers are needed to fill in the gap created in the center of the truss. This trait is passed on to its hybrid progeny. A high percentage of Hardgrove elepidote crosses contain R. fortunei , and those that do have this characteristic. Also, it often results in rangy seedlings.
Rhododendron forrestii ssp. forrestii Repens Group (and all other forrestii varieties) has beautiful depth of color, but the plant cannot bear the Eastern summer heat. This is passed on to next generation hybrids and often beyond.
A very interesting example of positive/negative in the same plant is R. 'Elviira' ( R. brachycarpum as ssp. tigerstedtii x R. forrestii ssp. forrestii Repens Group). It is bud hardy to 30F (-34C) (from brachycarpum ) and a deep red (from forrestii ) but impossible to grow successfully in the interior Northeast because of lack of heat resistance. Should we try to baby 'Elviira' in order to get at those luscious red genes or not? This is why hybridizing is a continual series of evaluations and decisions. It can be a draining experience, but, oh, what fun...

Which Plants to Use As Basis of Program
If you are starting from scratch (or starting over) this is where important decisions need to be made. The following are some I would choose (and have chosen) in the quest for the super-tough:
1. R. brachycarpum as ssp. tigerstedtii (Finland), hardy to 38F (-39C), has light pink to white flowers and good, shiny somewhat bullate foliage, and it absorbs/passes on colors used with it (as seed or pollen parent). See 'Elviira' discussion.
2. R. brachycarpum ssp. brachycarpum (var. formerly known as roseum ) is a reddish dwarf form with a very compact habit. It is heat and sun tolerant in my garden (and in Japan where Dr. Yasayuki Doi has used it in developing some intriguing pure red dwarfs. See Spring 2001 issue of the Journal, p. 103). It is hardy to 30F (-34C).
3. R. x nikomontanum (a natural hybrid of R. aureum x R. brachycarpum ) is hardy to 25F (-32C). It looks exactly as one would expect and is an excellent parent. Gable used a "yellowish brachycarpum." This may have been it. Joe Becales (Glen Mills, Penn.) has a cross of R. x nikomontanum x 'Roman Pottery' (Fabia Group). It has lovely orange hues and is hardy to at least 15F (-26C). It should be used further.
4. R. 'Kullervo' (-28F, -33C, Finland) is a cross of R. brachycarpum as ssp. tigerstedtii x R. degronianum ssp. yakushimanum . It is more compact than tigerstedtii itself and has white flowers. It has been crossed with R. dichroanthum ssp. scyphocalyx 'Bohnen', a good orange. With two species involved (one with good hardiness) the prospects are promising.
5. R. brachycarpum , white form, crossed with 'Fred Peste' by Tom Ahern (Bethlehem, Penn.) resulted in a light red with a considerably darker red picotee. The colors are strong. While the bud hardiness is yet to be determined, of significance is the color. Crossing of a white brachycarpum with a dark red hybrid produced a red. It is therefore reasonable to conclude that R. brachycarpum is a "color carrier." The jury is still out on the heat resistance of the various forms of R. brachycarpum (and 'Kullervo'). Reports indicate that they are good doers. I have them, especially ssp. tigerstedtii , at the top of my list of tough developers.
6. R. catawbiense , white flowered, compact form, is a fine reliable interior Northeast parent. I do not recommend 'Catalgla'. Research has shown that it often develops a poor root system. This shows up after three or four years in many of its hybrids.
7. R. aureum (-15F, 26C). I know it can't take sun, doesn't like heat, etc., but it has yellow genes and passes them readily. When you get to second generation hybrids it can be an asset, especially if you are interested in dwarf or low growing plants. Capt. Richard Steel's (Nova Scotia) R. aureum x 'Prelude' is a fine plant and has been crossed successfully with a variety of things.
8. 'Delp's Dream', a cross of 'Si Si' (ssp. yakushimanum x 'Gold Mohur') x 'Serendipity' ⁴ is reasonably hardy (-12F, -25C), semi-dwarf and compact. It is a creamy yellow, but came through our hot, dry summer of 2002 in fine shape. Occasionally you may decide to play a hunch. This is one of mine.
9. 'Evening Glow' ( R. fortunei ssp. discolor x Fabia Group) is a Ted Van Veen beauty that has withstood the passage of time. Just like the Energizer bunny, it keeps on ticking - an example of the whole being greater than the sum of its parts. I believe it is bud hardy to lower than rated (-5F, -21C), is sun-tolerant and very heat resistant. It also survived the summer of 2002. I am not sure of the reason(s). I also have mature plants of 'Balalaika', 'Amaretto' and 'Abendsonne', all containing R. dichroanthum ssp. scyphocalyx (as does the Fabia Group). There was a little leaf burn on 'Amaretto' but nothing of real significance. They all made it through the 2002/2003 winter and bloomed in spring 2003. Perhaps the "knock" on R. dichroanthum hybrids in the interior Northeast is not totally warranted. They certainly represent a source of orange genes in the program. A consideration.
10. 'John Paul II' (-20F, -29C) is Joe Minahan's masterpiece. It is a cross of 'Mars' x ('The Hon. Jean Marie de Montague' x 'Cheer'), with a full, glowing truss with just a touch of a blue cast and with fine foliage and plant habit. Some scarlet genes and additional hardiness (I know I am being picky) would make it exactly what we are aiming for. By any standards it is a terrific rhody. Congratulations, Joe!

11. 'Fashion Plate'* is a stunner from Joe Becales's garden. It has everything except the 25F (-32C) bud hardiness we are aiming for. Hardy to 15F (-26C) (possibly lower), it takes extreme heat and summer sun without flinching. There is no air circulation in Joe's lower garden. 'Fashion Plate'* has a full truss and each flower is 5 inches in diameter! A beautiful clear deep yellow, the truss holds up for eight weeks and literally drips gobs of pollen. The parentage, you ask? It is: ([Gable's cream fortunei x R. vernicosum 'Mount Siga'] x 'Mary Belle') x ([('Dido' x R. chlorops 'Lackamas Cream') x R. lacteum ] x 'Golden Star'). It looks like a genetic lottery...but if we take a minute to look more closely at the parentage we can find some things worth noting. First, let's break down the components: (this is a good exercise).
Seed parent = (species x species) x hybrid
Pollen parent = ([hybrid x species] x species) x hybrid
This totals seven plants. Two thirds (2) of the seed parents are species; one half (2) of the pollen parents are also species. All of the species are cream, medium or dark yellow. These represent about 60 percent of the total cross. Significantly they possess the least variance in the total gene pool, the species being "pure" (not containing competing coloration genes). Thus, fewer seedlings need to be grown to blooming size in order to find suitable plants. This is opposed to a cross consisting of five, six, seven or more hybrids. ⁵ The lesson is "simple is usually better." The key, however, is to chose the best simple "pieces" in order to create the ideal "whole."
'Fashion Plate'* represents a well thought out effort and not just a mlange of yellow rhodies thrown together with crossed fingers and high hopes. It has been said, "luck is the residue of design." I believe that this plainly represents that statement. A number of yellow hybrids have been developed with 'Fashion Plate'* and more are on the way. Some such as 'Janet Blair' x 'Fashion Plate' show real promise but not in the 25F (-32C) range.

12. An unnamed cross is the cross ('Vinecrest' x ['Janet Blair' x 'Donna Hardgrove']) x 'Weston's Hardy Yellow', a cross by Allan Glassman (Allentown, Penn.), and seed sown, raised and named by John Doppel (Lenhartsville, Penn.) If you want to see the ultimate test garden, visit John Doppel's place on one of the garden tours during the 2004 convention. Plants here receive no protection from the elements, including deer. Mother Nature rules supreme in this semi-alpine atmosphere. There is a view from John's back porch that covers 37 miles. He grows more fine hardy hybrids than anyone I know. Already a true yellow, this unnamed cross is among the best. He considers it a work in progress and looks to improve on growth habit and hardiness. If you are seeking direction with regard to "tough" hybridizing, talk to John.
13. 'Camp Hill Sunrise'* is the cross 'Mary Belle' x 'Odee Wright' (-18F, -28C). No, that is not a misprint. Minus 18F (maybe lower) is correct. The parentage may say "no," but Mother Nature says "yes"! The foliage is as pretty as anything you will see this side of Oregon - shiny (like 'Odee Wright'), bullate and leaves over 12 inches long and 5 inches wide, with a full yellow truss to top it off. Joe has about twelve siblings growing, all similar in plant habit with flowers ranging from peach-apricot to pure yellow - an outstanding result from one cross. They survived the summer of 2002. A cross of 'Camp Hill Sunrise'* should be made with R. x nikomontanum , R. brachycarpum as ssp. tigerstedtii or 'Kullervo'.
14. 'Janet Blair'. Personally I don't think highly of 'Janet Blair' as a rhody. I used to grow it, but I gave it away and replaced it with something having "more character." It still lacks character for me but, oh, those genes! Over the last twenty years more beautiful hardy hybrids have been developed with 'Janet Blair' as a parent than any other Northeastern rhody I can think of. They are usually in the yellow/cream/orange hues. Here are a few:
Jim Barlup, dean of the yellow hybridizers, has a new entry: 'Mindy's Love' x 'Janet Blair'. While not yet tested in the Northeast, it will probably be hardy to 5F(-21C) to 8F (-22C). An intermediate step, I grant you, but a good one. Jim says it is a good yellow, and that's enough for me. Jim has crossed some of his earlier hybrids (most hardy to 0F, -18C) with some Eastern hardier plants in an effort to produce the color, plant habit, etc., of his well-known creations ('Mindy's Love', 'Recital', 'Invitation') and the hardiness and heat tolerance of the other parent. Some of his are crosses that might work as an intermediate step in the tough program: ('Mindy's Love' x 'Janet Blair'), ('Janet Blair' x 'Summer Peach'), ('Invitation' x 'Janet Blair'), ('Percy Wiseman' x 'Recital'), ('Percy Wiseman' x 'Summer Peach'), ('Amber Touch' x 'Rio') and ('Wind River' x 'Janet Blair'). They should all be hardy to at least 5F (-21C) and some to 10F (-23C).
Quite a few years ago Joe Becales crossed 'Janet Blair' (s) with 'Goldsworth Orange' (p). One plant is a yellow-orange blend that so impressed David Leach that he returned to Joe's garden the same year in order to take some cuttings. He felt it would make a fine addition to his hybridizing program. It is hardy to 15F (-26C).
John Doppel also has a 'Janet Blair' entry: ('Janet Blair' x 'Whitney's Orange')#1. The flowers make it look like a sibling of 'Whitney's Orange', but it is obviously a lot hardier. 'Janet Blair', named after a lovely Pennsylvania-born stage and screen actress of the 1950s and 1960s, is another rhody that passes color to its progeny and also adds considerable hardiness. There is quite a long list of other 'Janet Blair' successes - too long to name here. Let's add this lovely lady to our list of rhodies to work with.
Here are some more considerations:
15. 'Capistrano' (-20F, -29C) is the best hardy commercial yellow. A must because of bud hardiness and depth of yellow color. Also it can take Northeastern heat. Top of the list.
16. 'Vinecrest' (-15F, -26C) is almost as good as 'Capistrano', although the color is not quite as "brilliant."
17. 'Blazen Sun' (-15F, -26C) by Lanny Pride bears orange-pink flowers.
18. 'Wizard' (-15F, -26C) is the cross 'Catawbiense Album' x Fabia Group. It is an old-timer with orange flowers and hardy. It seems to have been passed over and almost forgotten, much like some women's fashions. The genes are there for orange and hardiness and should be worth a look in someone's program.
19. 'Golden Harvest'* (-12F. 25C) is the cross 'Dexter's Champagne' x ( R. fortunei ssp. discolor x R. wardii ). It is Dr. Bill Rhein's fine compact yellow with a good truss and takes the heat.
20. 'Kathy Lou' (-8F, -22C) may be hardier than 'Golden Harvest'. An unknown cross, probably containing 'Whitney's Orange', produced this gem grown by Lou Seeds (Bethlehem, Penn.). It is not as hardy as we want to work with but you have to cut it some slack because it is as strong an orange as I have seen grown in the interior Northeast.
21. R. brachycarpum as ssp. tigerstedtii x 'Crest' (-15F, -26C), brings us back to Joe Becales. It has good color but is rangy, as are many 'Crest' hybrids, but definitely on the right track because we capture yellow genes plus hardiness. Just keep the process moving along.
Another group of plants worth considering are those produced in the Weston hardiness factory in Massachusetts: 'Arctic Gold' (-20F, -29C); 'Weston's Hardy Yellow' (-15F, -26C); 'Big Deal' (-20F, -29C); and 'White Dimples' (-20F, -29C). While none of them are outstanding yellows, they carry and more importantly pass on yellow. One very successful cross made by Tom Ahern is 'September Song' (0F, -18C) x 'White Dimples'. The seed was grown by John Doppel and Howard Kline (Leesport, Penn.) and produced seedlings of varying color (off-white, cream, colors similar to 'September Song', and a brilliant clear yellow of excellent color). The exact parentage of these Weston hybrids is not known, but they offer additional building blocks to the program.

We have examined the visible plant elements (flower color, truss size and shape, plant habit, etc.) and those that we cannot see (hardiness, heat and sun tolerance, resistance to soil pathogens). They must be joined together, genetically, to create the race of hybrids we are looking for - the tough yellow, red or orange flowered rhodies. Utilizing some of the things mentioned earlier, here is how I would approach it, as shown in the Table. (The aim in this particular exercise is, obviously, yellow flowers.)

Table 1. Crosses for producing hardy yellow flowered rhododendron hybrids.
Plant	Nickname	Hardy to:
A. R. brachycarpum ssp. tigerstedtii	Tiger	-38F
B. 'Capistrano'	Cap	-20F
C. 'Fashion Plate'	Plate	-12F/-15F
I.
(A x B) = D (B x A) = E (D x C)* = F (C x E)* = G	*(F 2 , F 3 , F 4 , etc.).
A Section . (G** x D) = H (G** x E) = I (F** x D) = J (F** x E) = K	**Plus best selected siblings. The number selected and used for future breeding is up to the hybridizer.
II. Using the nicknames, the above formulas would read: (Tiger x Cap) = TigerCap (D) (Cap x Tiger) = CapTiger (E) (TigerCap x Plate)** = TigerCapPlate (F) (Plate x CapTiger)** PlateCapTiger (G)
B Section . The crosses in B Section could be reversed. The B Section can be advanced by additional crosses. Plug in your own selections. (PlateCapTiger x TigerCap) = H (PlateCapTiger x CapTiger = I (TigerCapPlate x TigerCap J (TigerCapPlate x Cap Tiger) = K
III. An alternative set of crosses using the same three plants:
(A x C) = L (C x A) = M (L x B)* = N (B x M)* = O	*(F 2 , F 3 , F 4 , etc.).
A Section . (O x L) = P (O x M) = Q (N x L) = R (N x M) = S
IV. Using the nicknames, the above formulas would read: (Tiger x Plate) = TigerPlate (L) (Plate x Tiger) = PlateTiger (M) (TigerPlate x Cap) = TigerPlateCap (N) (Cap x PlateTiger) = CapPlateTiger (O)
B Section . These crosses could be reversed. These crosses should result in the 25F range.
(CapPlateTiger x TigerPlate) = P (CapPlatetiger x PlateTiger) = Q (TigerPlateCap x TigerPlate) = R (TigerPlateCap x PlateTiger) = S

When you have developed some promising seedlings and you are waiting to make further advancements, is there something more you can do? Another old adage: "If something can go wrong, it will - and even if it can't, it might!" It sometimes seems as if Nature plots against our well-intentioned attempts to improve upon the existing flora. Drought, hail, excessively high winds or snow that cause tree branches or the entire tree to fall on the garden can occur. We have all lost some valuable plants because of such occurrences. What to do? Be smart and plan against such things. Take cuttings of seedlings that show promise and root them. Some people have more talent in this area than others. Rather than relying on my ability, I send my cuttings to the Van Veen Nursery. They are professionals at rooting - it's what they do for a living. Many of the most experienced hybridizers work with them. They advertise in this journal.
Starting over...I am indeed doing just that since my return four years ago from Houston, Texas (a.k.a. rhododendron Alcatraz). I have restarted my hybridizing efforts, albeit somewhat late in the game, with the same enthusiasm I had almost forty years ago. Periodically you ask yourself, "Is it worth the effort?" Yes. Are there any rewards other than talking with interesting people about something you love to do? A few. Why should we pursue such a difficult goal? It is in the application of logic - trying to overcome genetic obstacles in the laboratories of our back yards and basements - that spur us toward success. It is said, "A man's reach should exceed his grasp." That, in the proverbial nutshell, is what it is all about.
I don't know if I will be around to see any of my own "super-toughs" in bloom, but I hope to see some of yours. Stay in touch.

* Name is not registered.

Endnotes
¹ This includes Massachusetts, Pennsylvania, New Jersey, northern Maryland, Connecticut. It does not include Long Island, Cape Cod, coastal Connecticut, coastal New Jersey and the Philadelphia-Wilmington area.

² Thomas Schilling.

³ Specifics for which color a plant would be used.

⁴ R. 'Serendipity'. Basil Potter's R. aureum x R. degronianum ssp. yakushimanum (-20F) (direction of cross unknown).

⁵ The unexpected hardiness comes from a combination of A. the "hybrid hardiness" theory, and B. the dominant seed parent which contains hardy species (2/3 of the genetic makeup) and a hardy hybrid (1/3 of the makeup). If this same cross were done in reverse, the seed parent becoming the pollen parent, it would be more difficult to produce a plant with the hardiness and color of 'Fashion Plate' in a seedling population of similar size.

⁶ This plant (and 'John Paul II') survived the winter of 1993/94 when temperatures in this area were below 20F for 3 plus days.

⁷ Make a copy of your records. You may lose the original. Don't depend on your PC to store valuable material.

Dennis Mac Mullan is a member of the Valley Forge Chapter.