by Susannah G. Cooper
R. maximum photographed by Robert J. McKenzie
Rhododendron is a member of the the Ericaceae (heath) family, which mostly consists of trees and shrubs which grow in acidic soil. The leaves can be evergreen or deciduous and the shape of the flower can vary from a tubular to funneedl. Species with both single and clustered flowers are found in this family. The fruit can be either a capsule or a berry[1].
The name rhododendron is from the Greek rhodon, meaning "rose", and dendron, meaning "tree"[2]. Its leaves are often a shiny green with a generally oblong shape. Rhododendron's leaves tend to crowd toward the tip of the twigs. The leaf bud is usually smaller than that of the flower, which is terminal and usually found within a cluster of leaf buds. The fruit is typically a capsule[1].
Horticulturists have been cultivating different species of rhododendron for centuries. R. hirsutum was the first rhododendron to be formally cultivated: it was introduced to Britain from Switzerland in 1656. In 1736, the second species of rhododendron, R. maximum, was imported to Britain from America. Peter Collinson, an English Quaker, and John Bartram, a Pennsylvania farmer, sold the species in London to garden enthusiasts. The species was not commercially successful due to the lack decorative quality and the late bloom of the flowers. The public enthusiasm about rhododendron led to much exploration for and importation of different species[3].
Rhododendrons are not only decorative plants; they have many other valuable attributes. Rhododendron is an essential part of the understory of the forest, the leaves are part of a deer's diet and it also provides cover for many mammals and birds[4]. Further, the wood is often used to make the bowls of briar pipes, the handles of tools, and small craft items[5].
The genus contains over 1000 species and is divided into five subgeni: Theorhodion, Pentanthera, Tsutsusi, Hymenanthes, and Rhododendron. Pentanthera has one section: Rhodora. Tsutsusi is divided into two sections: Tsusiopsis and Tsutsusi. Hymenanthes also has only one section: Ponticum. The subgenus Rhododendron has three sections: Rhododendron, Vireya, and Pogonanthum[2].
Please click here for a guide to identify species which are native to the southeast.
Soil: Rhododendrons, like most members of the Ericaceae, needs acidic soil. The optimum pH for rhododendrons is around 6 or less. The soil also needs to moist. Rhododendrons do not flourish in sandy soils because of problem with water storage; the genus typically does well in peaty soils and even in clay soils due to their ability to hold water [6].
Climate: Rhododendrons typically grow in partially shaded areas, like the understory of a forest. They are often found on stream banks, ridges and moutain balds [1]. "The Rhododendron continuously dispels moisture vapour through the stomata of its leaves and it diffuses more than it takes in" [6]. Therefore, rhododendrons require climates with ample rainfall [6]. The plants do well in places with "mild winters and humid, cloudy summers" [7].
[1]Swanson, R.E. 1994. A Field Guide to the Trees and Shrubs of the Southern Appalachians. Johns Hopkins University Press: Baltimore. p.303-306
[2] www.netaxs.com/~mckenzi1/intro.html
[3] Street, J. 1987. Rhododendrons. Globe Pequot Press, Chester, Connecticut. p.13-18
[4] www.fs.fed.us./database/feis/plants/tree/rhomax
[5] Duncan, W.H. and Duncan, M. B. 1988. Trees of the Southeastern United States. University of Georgia Press, Athens, Georgia. p.220.
[6] Barber, P.N., and Phillip, C.E.L. 1967. The Rothchild Rhododendrons: A Record of the Gardens at Exbury. Cassel: London.
[7] www.botany.com/rhododendron.html
