Breeding Evergreen Azaleas for Hardiness and Late Flowering
Dr. W. L. Tolstead
Elkins, West Virginia
When I first started breeding rhododendrons in the early 1960s there were two alternative choices from which to work: the evergreen azaleas (subgenus Tsutsusi which includes the former subseries Obtusum) or the native Rhododendron calendulaceum (sub-genus Pentanthera which includes the former subseries Luteum). Fortunately or unfortunately, I decided to work with the evergreens, probably because of their glamour and because they are more well known.
From 1960 through 1986, I grew 136 seed collections of evergreen azalea crosses. Of all these, there were only four groups that demonstrated special promise to fulfill my objective of producing a plant that could tolerate extreme low temperatures and also present a delayed flowering characteristic in order to escape the late frost of this area. These four standout groups are: 'Willy' x 'Boudoir', 'Susan' x R. kiusianum, R. kiusianum, and a fourth miscellaneous group.
'Willy' x 'Boudoir' (Gable varieties) produced a clone that was named 'Leonard'*. This clone was selected because of its unique flower, which is a dark lavender. Because of this trait I suspect it is a remote segregate from R. yedoense background.
From the cross 'Susan' (Gable) x R. kiusianum another clone was taken and named 'Doctor Smoff'. It is late, small flowered, and somewhat dwarfish in size. Flowers are pink and light lavender.
In 1969, I received seed of R. kiusianum from the U.S. Department of Agriculture. This seed group, crossed with R. nakaharai, yielded a clone that was named 'Creeping Joe'. These plants are also dwarfish in size, very hardy, and small flowered. They closely resemble the domesticated Easter azalea, which was developed in the lowlands of Japan and although sophisticated in appearance is very tender and unsuitable for colder climates.
The fourth group is a small population of miscellaneous plants from the remaining 132 seed collections that managed to survive. Three clones were taken from this group and named 'Cornhusker', 'Elkins', and 'Ames'. The precise genetic background of these clones is not clear.
All four of the above groups fulfilled my objective of producing a viable, hardy, late flowering plant that could tolerate extreme low temperatures (-26°F in 1986; -28°F in 1987). It must be mentioned, however, that besides the fourth small group, the remaining 132 collections produced nearly nothing. This illustrates a sound genetic principle: "You can't make a silk purse from a sow's ear." In other words, in search for hardiness, it's best to select plants from areas that have been cold for ages, such as the high mountains of Kiushu and Korea.
A study such as mine will probably never be repeated. As Edgar Allen Poe's raven quoth, "Never - nevermore."
Dr. W. L. Tolstead, Professor of Biology, Emeritus, at Davis & Elkins College in Elkins, West Virginia, is a member of the Great Lakes Chapter.
* Name is unregistered.