Rhododendron in Primeval Culture
Elsworth Brown, Chattanooga, Tennessee
Introduction
This is a report of an investigation which has for its objective the determination of the nutritional requirements of rhododendron. It is a continuing investigation, and subsequent reports will be in order. Because I have gone into the wilderness for basic information, I believe this report, in a series of "installments," may be of interest to botanists.
"Wilderness," writes Benton MacKaye in the October 1950 issue of The Scientific Monthly, "is the perfect norm; it is wild or untamed land as distinguished from domesticated...wilderness is a reservoir of stored experience in the ways of life before man."
American rhododendron species have had rather scanty treatment in horticultural literature; virtually nothing has appeared comparable with the works of English rhododendron enthusiasts. The researches of Kingdon-Ward, Cox, and Rock, and of the American A. H. Wilson, have turned up so much information about eastern Asiatic rhododendron that the lack of research on our native species has tended to suggest that because ours is a smaller field it may not be of much importance. Smaller? Doubtless so but not consequently unimportant.
I think there may be more to the story than has been unfolded. Some botanically trained horticulturists have told me they think the domestication of some of the native species should have attractive commercial possibilities. While apparently most of the members of the American Rhododendron Society seem engrossed in English importations some are wondering what modern technique could do with American native rhododendrons several of which are known only to botanists.
Leaving the "commercial possibilities" to the business people, I am content to remain merely a hunter and observer.
The "satisfaction" a flowering plant exhibits as regards its setting, its state of health and exuberant growth, may be shown by the degree of its development above what we have come to regard as the normal or the "expected."
By careful observation of the environment of rhododendron in true wilderness setting, we may hope to determine the conditions by which we may synthesize the primeval culture in practical nursery operations. By such artificial bringing in of the wilderness, we may provide optimum performance of ornamental wildings that have been set out in the home gardens and in public places.
Two geologic situations especially favorable to rhododendron exist in Tennessee-the soil resulting from decomposition of the rocks of the great Unaka range and the sandstones of the Cumberland mountains.
For superlative development, a weather factor importantly figures in the high mountain rhododendron growths along the Tennessee and North Carolina state line.
In this compilation of notes on the primeval culture of rhododendron, the author hopes to describe several species of both the evergreen and the deciduous groups; and shall select, for detained pertinent description, localities where one or more conditions of soil or of weather, or both together, very obviously have favored optimum plant development. In this first paper, we shall go to a station immediately south of where Monroe County, Tennessee, joins the corners of Cherokee and Graham Counties, North Carolina.
Rhododendron On Little Junction
Little Junction is a peak approximately 5,000 feet above sea level where Rough Ridge, of Monroe County, joins State Ridge on the Tennessee and North Carolina state line. It is an upheaval of the Ocoee formation (4) with frequent exposure of iridescently tinted, dark bluish rock. Occasionally, extrusions of white quartz appear. The rock is friable at the exposed surfaces, and factures into boulders and angular fragments until finely integrated with the top soil. The top soil is shallow, with the solid rock of the mountain protruding at many points. The bottoms of most of the ravines radiating from Little Junction are strewn with small boulders and angular fragments. A sample of this rock was powdered in a mortar and submitted to the Soil Testing Division of the Tennessee Crop Improvement Association in Nashville. The laboratory report rated the pH of this rock at 5.7 and indicated "very high" available phosphorus and potash.
The forest is dominated by northern red oak (
Quercus borealis
) of low, spreading tops. Yellow birch (
Betula lutea
) contributes many shrubs to the undergrowth and sprouts of American chestnut (
Castanea dentata
), and an unidentified species of
Crataegus
brightly red-fruited in September help fill in the denser places. June to October, the forest canopy shuts out about half the skylight.
Next to the south of Little Junction on State Ridge is a partially open area designated as Big Grassy Top, and the "bald grass" (
Danthonia compressa
) and associated ground cover complex extend on to the forest floor of Little Junction except at the very apex of the peak. Worth and south and within a few hundred feet of the apex are perpetually flowing springs of cold water, trickling through roughly scattered rock fragments-the southward spring to Rough Ridge Creek and the northward spring to Sycamore Creek, both on the Tennessee side. The eastern slope drains into Peckerwood Creek, North Carolina. All are tributaries of the Tellico River. Where the water divides-that is the state line. Eastward, it is the property of the heirs of Mercer Fain who acquired 10,000 acres here 70-odd years ago; and westward Little Junction lies in the Cherokee National Forest.
Average annual precipitation here has been 71.46 inches for the eight years since the Tennessee Valley Authority moved the Haw Knob recording rain gauge from the Whig Meadow to the Hog Jaw Gap clearing, right at Little Junction, in 1941. In 1938, the snowfall and rainfall on nearby Whig Meadow totaled 101.13 inches. In 1949, Little Junction had 88.20 inches precipitation with 13.88 inches coming in May and June while the azaleas were getting ready to bloom, followed by 31.02 inches the next three months while they were maturing their seed capsules and setting flower and leaf buds for the spring of 1950. Here, then, during the five months' season of activity, these azaleas had 44.40 rainfall which may be compared with Knoxville's average annual precipitation of officially reckoned at 44.77 inches, and Johnson City's 43.48 inches. (1)
According to the statistics which the author has examined, (5) the precipitation record for Little Junction is only exceeded in volume, in Tennessee, by that of Clingman's Dome in the Great Smoky Mountains National Park.
Flame azalea (Rhododendron calendulaceum) dominates the rhododendron "population" of Little Junction. There are a few stands of R. catawbiense, and at least one representative of the species
R. arborescens
. Many years ago, some member of the family of the late Jasper Fain found on the eastern slope a specimen of what the author tentatively has identified as R. furbishii; and it was successfully removed to the hamlet of Fains, N. N., where it may still be seen, blooming two weeks after the flame azalea is at its best on Little Junction. The hamlet of Fains is about 1,200 feet lower than Little Junction. In connection with this reference to R. furbishii, it is interesting that, in his book "Azaleas, Kinds and Culture." H. Harold Hume (3) speculated that this azalea "perhaps" may be found "in the Great Smoky Mountains at elevations above 3,000 feet."
The latest discovery, reported to the author by Fred J. Fain, North Carolina game warden, apparently is a relative or variety of R. furbishii which Mr. Fain says has two instead of one petal splotched with orange yellow. This possibly new azalea has been removed to Fains for convenience of observation.
The dominant flame azalea on Little Junction may reach an extreme height of 16 to 17 feet as observed by the author, and Fred J. Fain has found it even higher. Such height, however, appears to have been induced by the closing in of associated shrubbery, compelling the azalea to exaggerate its upward growth in order to obtain sunlight. In the average setting, it will usually be found in shrubby clumps, up to 10 feet in height, with many stems around 2 inches in diameter, and with as many as 25 stems greater than 1/2 inch in diameter to a clump. (Diameter here is taken at the ground.) Cross section of average 2-inch stems reveals about 30 annual rings.
The preliminary labor by which were obtained the stems exhibited with the reading of this paper was performed by one or more black bears. The resident game warden so assured the author as the two, in June, 1948, found several damaged azalea bushes on Little Junction. At blossoming time, in June, the native wild azaleas are subject to leaf gall produced by the parasitic fungus
Exobasidium vaccinii
. These are pathologic distortions of newly appearing leaves. Children used to go into the woods and gather leaf galls from native azaleas, calling them "honeysuckles." The author has eaten them to "stretch out" a vanishing supply of carried drinking water while on mountain trips. Apparently the bears like "honeysuckles," too. Some of the fresh, lush, brightly green galls were more than an inch in diameter. Those on the tips of long, limber branches, which the bears could not reach from the ground, escaped harvest; and in some places under observation in June of both 1948 and 1949 were conspicuously grouped with the flowers.
Soil collections from around the roots of large clumps of flame azaleas on and near the peak of Little Junction consisted of black, gritty, peaty material. Much of it appeared to be residue of the natural leaf mulch which accumulates naturally, often found 10 to 12 inches deep while fresh and loose in the fall, and settling, by blossoming time to about half that depth. At the bottom, the mulch constantly is decomposing into the top soil.
Samples 'of the soil at the roots of the larger azaleas selected for photographing were examined on the spot for acidity. Duplicate samples were sent to Tennessee Soil Improvement Association in Nashville for determination of the available phosphorus and potassium plant food, and also for the pH to check the author's findings. In general, the phosphorus was found to be "high," the potassium "very high," and the pH varied 4.50 to 4.2. This acidity range conforms to that which is regarded as characteristic of highland peat. In ten tests, Wherry found optimum pH for
R. calendulaceum
to be 5.5, and tolerance down to 4.5 was observed.
Authorities Cited
- Climate and Man, 1941 Yearbook of the United States Department of Agriculture, Washington, Government Printing Office, Pages 1119-1128.
- Account of the finding of the large "pink" azalea at the Jasper Fain home at Fains, N. C., was related to the author June 15, 1949, by Fred J. Fain and his, mother, Mrs. Jasper Fain, whose husband (deceased 1938) was a son of Mercer Fain, pioneer settler in this Unaka mountain region.
- Hume, H. Harold: Azaleas, Kinds and Culture, New York, 1948, The Macmillan Company. Page 35.
- Safford, James M. (state geologist): Geology of Tennessee, Nashville, 1869, S. C. Mercer, printer to the state. Page 186, section 434.
- Tennessee Valley Authority-letter to the author from James Smallshaw (hydraulic engineer), February 14, 1950. Average annual precipitation on Clingman's Dome: 85.14 inches.
- Wherry, Edgar T. (U. S. Bureau of Chemistry): "Soil Acidity-Its Nature, Measurement, and Relation to Plant Distribution" in 1920 Annual Report of the Smithsonian Institution, Publication 2622, Washington, U. S. Government Printing Office. Pages 247268.