QBARS - v30n1 R. vernicosum aff. R. 18139

R. Vernicosum aff. R. 18139
Gable Study Group, Potomac Valley Chapter
George W. Ring, Chairman, Caroline Gable, Col. and Mrs. R. H. Goodrich,
Mr. and Mrs. C. R. Haag and George T. Miller

R. vernicosum aff. Rock #18139 was grown by Joseph B. Gable from seed collected by Dr. Joseph F. Rock in China in 1929. It differs from R. vernicosum which has two to three inch white to rose flowers. 1
From the Gable seedlings, two superior clones were propagated. Clone # 1 is a four inch clear peach pink with no trace of blue. It is hardy to at least -5 deg. F. Growers on the East Coast rate it 4/3. The cover photograph shows Clone # 1.
Clone #2 is the same four inch size but slightly more pink than peach. Both tend toward yellow as the florets age. Clone #2 is the hardier, to -10°F. It forms a mound shape at maturity. Unless growers own both clones, it is hard to tell the difference. Blooming the first or second week in May at Gable's Nursery at Stewartstown, Pa., plants attain eight to ten feet after many years. The foliage, while not superior, offers a "second show": the bracts on the new growth are like scarlet ribbons.
Respondents to the Gable Study questionnaire place R. vernicosum aff. R. 18139 from North Carolina to Nova Scotia on the eastern seaboard, although in Nova Scotia flower buds only occasionally survive the winter. Undoubtedly there are other seedlings of R. 18139 growing in the U.S. and abroad. It is quite probable that some un-bloomed seedlings were sold by Mr. Gable. It is also evident that Mr. Gable was not the only subscriber to the 1929 Rock expedition who received this seed lot. Lord Aberconway exhibited R. vernicosum aff. 03788 in the 1972 Rhododendron Show in England 2 .
Researching of Mr. Gable's notes clearly indicates that the numbers 18139 and 03788 3 refer to the same seed lot.
Both Clone #1 and #2 are easy to propagate from July cuttings, which bloom in four to five years. With half shade and good drainage plants yield ample to heavy bloom.
While R. vernicosum aff. R. 18139 is not well enough distributed to be prominent as a parent, it has done well when used by Mr. Gable. Crossed with R. fortunei , cream, it yielded 'Mary Garrison', a beautiful blend to salmon yellow and pale red, destined for greater fame when its propagating problems are solved. From a cross with R. houlstoni came 'Dr. Rock', with the R. vernicosum aff. R. 18139 strongly influencing the flower color, and rated by its possessors at 4/4. Crossed on 'Mary Belle' R. vernicosum aff. R. 18139 produced 'Isabel Gable', coral in bud and opening to flesh pink. All the known hybrids of R. vernicosum aff. R. 18139 appear to be heavy bloomers. Hybridizers on the East Coast have used both clones extensively in crosses, and seed has been offered in the ARS Seed Exchange. So there are many hybrid seedlings coming along with this excellent parent in their make up. Miss Caroline Gable has furnished R. vernicosum aff. R. 18139 cuttings to the Species Foundation.
The authors are indebted to all those who responded to the Gable Study Group questionnaire, which made this article possible.

1. Rhododendron Handbook, Part One, Rhododendron Species, Royal Horticultural Society (1967), p. 167.
2. Rhododendrons 1972, Royal Horticultural Society, p. 59.
3. Rhododendron Handbook, op. cit., p. 246.

There is some controversy about the Rock Collection Number under which this plant is being grown. Some experts on the Rock expeditions have said there is no such collection number. Others suggest that the number R. 18139 may be the result of a transposition of figures somewhere along the line. Until the question is settled, the identification R. vernicosum aff. Rock # 1813 9 will continue to provide an adequate means of identifying the two clones under discussion. The Editor.
The Gable Study Group has received this additional information from the U.S. National Arboretum since sending the above article. "Seed collected from shrub 5-8 ft. found on alpine slopes at 14,500 ft. altitude, Mt. Siga, s. w. Szechwan, in September-October, 1929, J. F. Rock. Seed received January 10, 1930 from the National Geographic Society, Washington, D.C. by the United States Department of Agriculture who assigned the Plant Introduction number 84054 in 1930." Neither the National Geographic nor the USDA assigned the 18139 number.