JARS v51n4 - Tips for Beginners: Hybridizing Notes - Crossing East to West

Tips for Beginners: Hybridizing Notes - Crossing East to West
Jim Barlup
Bellevue, Washington

As a West Coast hybridizer, my goal is to merge the wide range of Western colors with Eastern hardiness and thereby produce new plants for hybridizers and growers on both coasts. Here in Western Washington we sometimes forget that occasional cold winters can take a heavy toll on our marginally hardy plants. It is to our advantage to work towards creating hardier plants. The challenge is to obtain hardier plant material as well as reliable information about the plants.
Hardiness data is incomplete and inconsistent. 1 Resource materials such as books and catalogs frequently contradict one another. For example, one catalog lists 'Noble Mountain' at -25°F and another lists it at 0°F. 'Judy Spillane' is listed at -5°F in one and -20°F in another. The hardiness information included with the name registration indicated the lowest temperature the plant was known to endure up to the time of registration. That doesn't mean that the plant won't endure lower temperatures. A cross of ('Mrs. J.C. Williams' x R. yakushimanum , Exbury selection), submitted for name registration in 1997, is rated at 0°F because that was the lowest temperature we had in this area since the plant was created 12 years ago. Knowing the hardiness of the two parents, however, gives more information. 'Mrs. J.C. Williams' and R. yakushimanum , Exbury selection, are both rated at -15°F. Therefore, it is reasonable to assume that a cross of the two would also be hardy to -15°F. Perhaps we could come closer to predicting the hardiness of a plant based on the hardiness of its parents if we have accurate information on the parents.
Articles on hardiness and severe weather damage are extremely valuable. I thank Max Byrkit for the information on winter plant damage in his articles "The Winter That Was, Part I" (1) and "Part II" (2). He writes that many Western hybrids were killed or had severe leaf damage. The lack of damage to Eastern plants was quite evident, with some coming through in very good condition. Examples are 'Merley Cream', 'Edmond Amateis' and 'Queen Anne's'. I can check Byrkit's information against the plants that I am using for hybridizing. This gives me an in-depth view of how a particular plant reacted in this severe cold and provides a basis for my own judgment.
Pat Halligan's article "Northeasterners Pick Their Favorite Gems" (3) also provides information that Western hybridizers need to better understand crossing East to West. I especially liked his division of Eastern weather into "milder cold" and "icebox." It provides more reliable information than books and catalogs and gives me choices from which to select. The Eastern hybridizers have learned which plants work the best for their hybridizing programs. They rate 'Janet Blair' and 'Scintillation' as two of the better plants we could use in our programs on the West Coast. Seedlings from a 1996 cross of ('Scintillation' x 'Snow Candle') have incredibly beautiful foliage.
Increasing hardiness in a plant is dependent on your choice of parents. If we cross a plant with a hardiness rating of 0°F with one at -10°F, do we accomplish enough to make it worthwhile? Much of my hybridizing is with yellow rhododendrons. Some of the yellow Eastern hybrids, such as 'Bud's Yellow', 'Phipps Yellow',* 'Butter'* and 'Golden Star' are generally 10 degrees hardier than most West Coast yellows. Does using these plants or pollen from these plants to increase their hardiness by 5 degrees validate such a new cross? I believe that it does. A 5°F increase in hardiness on either coast can be of value, particularly in yellows.
My feeling is that it would be more advantageous to use plants or pollen from plants that are even hardier, starting with at least a -15°F. For a yellow, I would cross 'Windsong' ['Nancy Evans' x ('Mrs. Betty Robertson' x 'Fred Rose')] with 'Janet Blair', 'Mary Belle' or 'Vinecrest'. To create an even hardier line, I would start with plants or pollen from 'Rio', 'Golden Gala', 'Casanova', 'Arctic Gold' or 'Capistrano', all of which are in the -20°F range or below. The resulting hybrids could possibly create a West coast yellow at -10°F or even -15°F. It's worth a try!
Some Eastern hybrids are difficult to find on the West Coast. If you are fortunate enough to find the plant that you are looking for, it may be small and require several years of growth before it blooms. I feel fortunate in acquiring what I consider core plants for use in my hybridizing program. These plants include 'Edmond Amateis', 'Scintillation', 'Besse Howells', 'Tuscany', 'Dexter's Champagne',* 'Peter Tigerstedt',* 'Wyandanch Pink' and 'Ingrid Mehlquist'. I also use some of Hans Hachmann's hybrids such as 'Fantastica', 'Goldbukett', 'Schneespiegel' and 'Hachmann's Charmant'. Since it may be years before crosses from these parents are available, submitting seed to the ARS Seed Exchange is a logical course.
Since the seed plant is usually the dominate parent, it is preferable to use Eastern hybrids as the seed parent. In cases where the pollen from the Western hybrid appears to be sterile, there is little choice except to use that plant as seed parent. I can use pollen from Eastern hybrids to cross onto 'Anita Dunstan', 'Nancy Evans', and many of their children such as 'Invitation' ('Anita Dunstan' x 'Lem's Cameo'), 'Horizon Lakeside' and 'Mindy's Love' ('Nancy Evans' x 'Lionel's Triumph') with the hopes of creating a hardier yellow. If you do not have Eastern hybrids to work with, consider using pollen from the ARS Pollen Bank. In 1996, the list had pollen from many Eastern hybrids that met my criteria for creating a hardier yellow. Sending pollen to the exchange is of value to other hybridizers.

rhodie graphic

As you acquire new plants for hybridizing, you have to evaluate them and try to understand what they can do for you. There is a lot more than hardiness that we need to consider such as heat and sun tolerance, drought resistance, root rot and soil adaptability. I'm very critical of growth habits, foliage, budding capabilities, etc. I have to be selective and discard any plants that are in any way questionable. Select only what you feel will give the quality and the hardiness that you desire. My 1997 seedlings of crosses of East to West show great foliage, seedlings of ('Tuscany' x 'Nelda Peach') and ('Rio' x 'Nelda Peach') have shiny, deep mahogany foliage. (Mindy's Love' x 'Janet Blair') seedlings are strong growing with glossy foliage. Seedlings from 'Amber Touch' (one of my best oranges) crossed with Eastern pollen shows great promise. This is all very encouraging. Within a few years we will see the results.
Commercial rhododendron growers that ship nationwide or worldwide have a need for new hybrids that are reasonably hardy to at least -10F. One West Coast grower ships 85 percent of his plants to the East Coast; therefore he has to limit the inclusion of non-hardy hybrids in his propagating plans. Hybridizers need to be aware of this if they want to distribute their plants to a national or international market.
Hybridizers need to have confidence in the crosses that they make, to know they are going forward with their goals and to be contented to wait four to eight years or more for the results. Do your research, talk to other hybridizers, find out everything you can about the plants you want to use for hybridizing, experiment and learn to rely on your own judgment. Share your knowledge, pollen, seed and plants with other hybridizers. Let's continue the exchange.

1.  Byrkit, M. 1995. The winter that was, part I. J. Amer. Rhod. Soc. 49:4, 231-232.
2.  Byrkit, M. 1995. The winter that was, part II. J. Amer. Rhod. Soc. 50:1, 41-43.
3.  Halligan, P. 1996. Northeasterners pick their favorite 'gems'. J. Amer. Rhod. Soc. 50:1, 2-5.

1 In 1993 the ARS adopted a new definition of cold hardiness: "Cold hardiness is defined as the temperature range through which damage to flower bud, leaf or plant structure can be expected to occur, in a plant at least five years of age and in good health. Flower bud damage is defined as that which detracts from a normal floral display. The range is give by two figures, expressed in both Fahrenheit and Celsius. The lower figure is the lowest temperature after which the plant has been observed to perform normally; the upper figure is the highest temperature after which cold damage has been observed."

* Name is not registered.

With this issue of the Journal, Jim Barlup, a member of the Cascade Chapter, concludes his series on hybridizing for the Tips for Beginners column.