Rhododendrons in the Southeast
By W. E. Bowers, Stone Mountain Ga.
During the last 10 year:, I have tested upward of 50 varieties of rhododendrons seeking to learn the extent of their adaptability to our particular lower Piedmont section here in the Southeast.
The Piedmont is that strip of rolling terrain some 75 to 150 miles wide, extending from Virginia southwestward through a section of the Carolinas into northern Georgia and northern Alabama. It represents roughly the upper limits of the Southeast's camellia japonica belt. The stretch lies between the lower reaches of the Appalachian mountain range an area too cold for camellias, and the Coastal Plains region where camellias are entirely at home.
The soils of the Piedmont are as well adapted to rhododendrons as to azaleas and camellias. Ordinarily they are well drained and by natural formation slightly acid. However they are short of organic matter. But of course that important constituent is none too difficult to supply.
Our seasons appear to be little different from those of the rhododendron-growing area of the Pacific Northwest, as I gather from the Government's Atlas of American Agriculture. I refer to the time of seasons. The big difference of climate of the two sections, as affecting the growing of rhododendrons, lies in their relative humidity. Up there the sun "steams." Down here it "bakes."
During our critical growing months of June, July and August we are favored with a great deal more rain than falls in the Oregon area. Our 20 year average for the 3 summer months is from 15 to 20 inches, that of the NW Pacific coastal range is only 2 to 6 inches. But this advantage doesn't mean that we are provided also with a humid atmosphere. The rapid drying-out effect of our "overhead" prevents that possibility. In other words, we have a dry atmosphere in summer regardless of good rainfall. Oregon and neighboring areas has a humid atmosphere during the same period despite much less rain. I have concluded that humidity has a profound bearing on the behavior of rhododendrons in general and on their flowering in particular. It is the limiting factor here as concerns their behavior.
Our climate during the fall, winter and spring seasons is not unfavorable for maintaining the rhododendron plant, fairly mild conditions with usually sufficient rain are present. But I consider that the line of demarcation in selecting suitable hardy ones is pretty well drawn. The A, B and C varieties may be relied upon to withstand our winters without trouble, the less hardy not. Our lowest temperature rarely ever descends under 15 degrees above zero, but we have sudden changes of temperature.
We have suitable soil, favorable rainfall and long growing seasons, as well as freedom from rigorous cold. Also I maintain adequate surface irrigation facilities. Yet some of my best-looking rhododendron plants have had flowers, others very few. R. 'Doncaster' is one in this category, R. 'Mrs. Holsford' another, as examples. I suspect that these to flower demand through inheritance even a damper atmosphere than those which flower better for us. Some other varieties, R. 'Alice' to mention one, struggles along and causes one to decide that they need something special. No bush of R. 'Alice' has ever bloomed in my garden.
Some hybrids that I have put out prove so poorly adapted to our conditions, or vice versa, that they never once show signs of liking it here. Many manifestly are so out of place that they seem particularly anxious to get the "dying-off" procedure over with in a special hurry. For instance, last spring I added some 20 varieties to our testing plots. We had an unusually favorable growing season. Yet the R. 'Blue Peter' which came to me well established in good Oregon soil and transplanted in April went out like a light in July. Mostly though a plant of a rhododendron, unsuited, drags along longer but never shows the least inclination to want to grow. Finally it is thrown out dead.
Most R. catawba hybrids, I conclude, are more or less tolerant of our conditions. One long-established (20 years) planting 60 miles further south in the lower edge of the Piedmont continues doing rather well, from last report. Plantings of these in our Atlanta area seem to do well, in some instances without any too much care. R. 'Roseum Elegans', R. 'Everestianum', R. 'Mrs. Chas. Sargent', R. 'Lee's Dark Purple' and R. 'Dr. Dresselhuys' are ones that have performed well for me.
Many of the Asiatic hybrid will grow here with more or less success, depending on the variety, and a great deal on the care exercised in planting and maintaining them. They definitely, though, appear to be more sensitive to our general conditions than the R. Catawba hybrids. I have settled upon four so far, which have proved consistently satisfactory over 10 years of trial growing. They are R. 'Pink Pearl', R. 'Bagshot Ruby', R. 'Cynthia' and R. 'Purple Splendor'. Another, R. 'Britannia' grows and buds up well but requires more protection from the sun to prevent leaf scalding. R. 'Cynthia' and R. 'Purple Splendor' do particularly well in sun. However all my plants now are growing in some degree of shade. I found that our sun, even as early as in May and June when the rhododendrons are in bloom, burn and disfigure the flower.
Currently in new plantings I have R. 'Loderi Venus', R. 'Loder's White', R. 'Jan Dekeus', R. 'Butterfly', R. 'Zuider Zee', R. 'Unique', R. 'Mars', R. 'Fagetter's Favorite', R. 'Souvenir of W. C. Slocock', R. 'Lady Chamberlain', R. 'Lady Milford', R. 'Betty Wormald', R. 'Elspeth', R. 'Earl of Athlone', R. 'Countess of Athlone', R. 'J. H. Van Ness' and a few others. The garden is littered with straggling plants of several more and other Asiatic varieties imported front Holland. For the present I am giving these imported rhododendrons the benefit of the doubt. Conditions of importation to which they were subjected might well have accounted for their failure to do well.
The rhododendron species? I have tried several, some more than once. Every consideration that results from a strong imagination and soil preparation know-how has been given the ones brought in. With one exception I have not a single plant of the various species to show for the effort expended. All that I have tried died and didn't consume much time in doing it, either the first year or the second. The list is not an extensive one but the experience I have had is sufficiently poignant to put me warily on guard hereafter. To mention some species I have tried to grow: R. ciliatum , R. callimorphum , R. fortunei , R. racemosum , R. thomsonii , R. smirnowii , R. yunnanense , R. griersonianum , R. sutchuenense , R. neriiflorum , R. leucaspis and R. williamsianum .
R. fortunei is the lone exception of the species that I still have. The Bureau of Plant Industry sent me 10 small plants of R. fortunei for testing in 1940. They performed beautifully for three or four years, but since have been doing very little. Nine of the 10 are still living, but have never bloomed. The plant that died managed to give a bloom in '45 or '46 but it promptly passed out from the effort.