Stalking the Wild Azaleas
By Norman Pellett
Department of Plant and Soil Science
Univ. of Vermont
Cold-hardy azaleas and rhododendrons often fail in the northern tier of states. The iron-clad rhododendrons are often severely injured in northern Vermont where mid-winter temperatures often reach -35° F and lower. Our recent studies showed that leaf, stem and flower tissues of rhododendron cultivars like 'Boule de Neige,' 'Nova Zembla' and 'Roseum Elegans' may be injured by expected low temperatures of near 0°F in early December. And yet, we occasionally find R. catawbiense (origin unknown) doing well in our coldest regions of Vermont. We suspect these were plants collected from the wild.
Rhododendron breeders have produced hundreds of beautiful selections hardy in states where winters are milder. We must look to other sources for hardy rhododendron material. The eastern native azaleas and rhododendrons offer a tremendous range and variety of plants. Some may be hardy enough for our climate.
In October, 1977, I started the search for native azaleas and rhododendrons of the eastern United States that might have some potential for the northernmost states. We need plants adapted to the coldest regions. I decided to collect several eastern shrub species from the northernmost part of the range and from high elevations. Travel funds are being provided for 3 years by the Northeastern U. S. D. A. Plant Introduction Station in Geneva, New York.
Why collect plants from the northern edge of the range? The notion that plants collected from the northern edge of their range are more cold-hardy has some support. Minnesota studies with Red-osier dogwood (Corpus sericea) and red oak (Quercus rubra) studies at Purdue University support this notion. In some cases plants from more southerly areas acclimate too slowly to survive November or December temperatures in northern states. To my knowledge, no one has tested this idea with azaleas or rhododendrons. As our collections mature, we plan to use laboratory freezing techniques to compare cold-hardiness of the various climatic races.
Species growing at high elevations where temperatures sometimes go below -20°F may survive winters in the northern U.S. The record low temperature on Mt. Mitchell, North Carolina, was -29°F. I am collecting several species in the Great Smoky Mountain National Park at near 5000 feet elevation, between 4500 - 6500 feet elevation in the Blue Ridge Mountains, from West Virginia Mountains and from the Catskill Mountains in New York State. Many azalea and rhododendron collectors have taken plants from these areas, but to my knowledge, no one has systematically collected from only high elevations and the northern edge of the range.
I have sought the advice of botanists, horticulturists and rhododendron enthusiasts in the eastern states. Numerous people have helped find these plants. Some have advised that I should combine my search with a search for improved forms. This certainly has merit, however, several obstacles have led me to rely on seed collection from stands in cold places that show floral characteristics acceptable to northern gardeners who now have little to choose from.
Several species are hard to root from cuttings, especially Rhododendron prinophyllum (roseum) and R. calendulaceum. Often there is variation in rootability among selections within a species. These factors discourage propagation by cuttings of selections made far from home. Often, the best selections in wild stands have already been taken by admiring gardeners. Hopefully, their qualities may remain in the gene pool of seedlings which we collect.
Small plants are collected in some cases, but I am reluctant to remove plants since collection is one reason for extinction in some areas. Regulations often discourage the taking of plants. It is easier to get permission to collect seed or cuttings.
Since azaleas are cross-pollinated, the seedling variation potential is staggering. We should preserve some of this diversity for the future. Our needs of the future may be different than the desires of today. In addition to cold-hardiness and large colorful corollas, we may need to select for drought tolerance and air-pollution resistance. There is a need to maintain the diversity among the climatic races of plants for future breeding.
Table 1 shows the coldest sites where I have collected. Undoubtedly, there are colder natural sites for some species than I have found. I hope readers will contact me with advice on sites for collection. Seeds are available to arboreta and experiment stations as long as the supply lasts. Unfortunately, supplies do not allow distribution to others at this time.
Table 1. Coldest Sites Where Native Azaleas
and Rhododendrons Were Observed
Species Location R. arborescens Wayah Bald, N.C. 5340 35° 09' Mt. Pisgah, N.C. 5720 35° 26' Cheat River, W. VA 3500 38° 37' R. calendulaceum Dolly Sods, W. VA, Tucker Co. 4000 38° 58' Mt. Pisgah, N.C. 5500 35° 26' Wayah Bald, N.C. 5300 35° 09' R. canadense Island Pond, VT 1300 44° 52' natural stands occur in Maine,
Quebec, Nova Scotia
R. catawbiense Roan Mountain, Tenn. Carter Co. 6280 36° 06' Mt. Mitchell, N.C. 6500 35° 46' Craig Mountain, N. C. 6320 35° 46' R. periclymenoides (nudiflorum) Dover Plains, N.Y. 500 41° 43' R. prinophyllum (roseum) Ithiel Falls, VT, Lamoille Co. 450 44° 39' Lake Dunmore, VT 600 43° 53' Summit, N.Y. 1900 42° 33' R. vaseyi Grandfather Mountain N.C. 5960 36° 06' Water Rock Knob, N.C. 6290 35° 28' R. viscosum Colonie, N.Y. 320 42° 43' Pelham, Mass 920 42° 21' Shohala Falls, PA 1240 41° 23' natural in various sites
near coast in southern Maine
and New Hampshire