Rhododendron Catawbiense at Low Elevations
by Robert L. Schwind, Atlanta, Georgia
Many of us in the Southeast involved in the culture of the genus Rhododendron are familiar with the extensive colonies of R. catawbiense found on the peaks of the higher mountains in the Southern Appalachians in Georgia, North Carolina and Tennessee usually above 4,000 feet elevation. There are few sights comparable to the beauty of this species as it blooms in profusion atop Roan Mountain and Mount Mitchell in late June and early July. The vigor and hardiness of R. catawbiense has figured importantly in the early creations of the so-called ironclads before the arrival of the exotics from the Orient. Even today these ironclads can usually be counted on to perform where others fail.
In the October 1919 issue of the Journal of the Mitchell Society, Dr. W. C. Coker of the University of North Carolina at Chapel Hill published an article describing a limited number of colonies of a different form of R. catawbiense found on certain precipitous bluffs overlooking streams in the lower Piedmont and coastal plain of the Southeast. Because of its apparent morphological and physiological differences from the mountain-top form as well as its isolation and location at low elevations, Dr. Coker chose to designate this form under the varietal name of "insularis". A few theories have been advanced in explanation of its appearance at low elevations, the more plausible of which is attributed to the Ice Ages. As the glaciers and their attending cold advanced gradually southwards, many species of plant life picked up and moved, as it were, to the South and East where they succeeded in surviving the frigid onslaughts. As the glaciers and the cold retreated northwards, isolated colonies of R. catawbiense evolved in adaptation to the warming trend and the present day torrid conditions of the coastal plain.
In May 1971 the writer, accompanied by his young son, Robert, and by Dr. Herbert Hechenbleikner of the University of North Carolina at Charlotte inspected colonies of R. catawbiense at three locations, namely near Wilson, N.C., at an elevation of 220 feet, near Lillington, N.C. at an elevation of 290 feet, and near Chapel Hill, N.C. at an elevation of about 280 feet. All three locations are in or adjacent to the coastal plain and are within the U. S. Department of Agriculture's plant hardiness zone 8a. Ordinarily the plants in these colonies begin blooming about the middle of April reaching their peak by May 1. Due to the lateness of the current season, the blooming was delayed and was approaching its peak when the writer and his companions visited the colonies at the end of the first week of May.
Casual observation readily discloses the more obvious similarities between the mountain-top and the low elevation forms of R. catawbiense, among which is the truss size and the flower color. The low elevation blooms range in color from a delightful light pink to darker pinks and even to a rosy pink which are free of the bluish tints characteristic of many mountain-top forms. Others were more characteristically catawbiense in their bluish and violet hues. All three colonies thrive on precipitous bluffs overlooking waterways under the cover of mixed hardwoods. In size the plants range from small seedlings to 15 foot shrubs. Generally the leaves are bright green, flat, and broadly elliptic. The current year's growth is frequently covered with a brown indumentum which rubs off at the touch.
In addition to the afore-mentioned colonies in North Carolina, the writer has inspected a similar colony in Cherokee County, Georgia at an elevation of about 800 to 1000 feet. The plants of this colony resemble those in North Carolina in almost all respects except shrub growth habit which in the Georgia form tends to be lower. The largest plant in Cherokee County was about 8 feet high; most of the others were in the 3 to 5 foot range.
The existence of the above-described colonies of R. catawbiense is of particular importance to rhodophiles in the Southeast where the cultivation of the genus is often frustrated by long, hot summers and concomitant root rot. Heat resistance and root rot resistance are perhaps the more elusive qualities lacking in most of the rhododendron material on the market. Cuttings and seeds have been collected from the colonies of R. catawbiense described above and are being propagated not only for their own beauty but also to serve as parents in the development of hybrid strains more suited for the Southeast and for introduction into the lower Piedmont and the coastal plain. During his recent inspection tour the writer collected trusses of several of the better forms and has used the pollen there from in making crosses with certain hybrids suitable in the Atlanta area, particularly those with a griffithianum and a griersonianum parentage in the hope that better heat and root rot resistant progeny will ensue.