Gerald L. Klingaman
Family
Ericaceae
Botanical Name
Rhododendron
Plant Common Name
Azalea, Rhododendron
General Description
The enormous genus Rhododendron comprises more than a thousand species. They are naturally distributed on every continent except Antarctica, Africa and South America. The highest concentrations of species occur in the temperate and mountainous regions of China, Japan, Korea and Taiwan. Grown for their showy flowers, rhododendrons are garden favorites worldwide and have been highly hybridized. There are more than 28,000 registered cultivars.
Plants in this genus are extremely variable in size, habit and floral form. Some are tall trees, but most are medium to large shrubs with mounded habits. A few odd species are epiphytes (tree-dwellers). They can be evergreen, deciduous or semi-evergreen. Rhody leaves are arranged alternating on the stem. They can be tiny or large and are usually elliptical or lance-shaped with smooth edges. Leaf surfaces can be smooth, glossy, hairy or scaled.
The flowers are generally borne in clusters, but some have single blooms. They appear at the ends of the branches, a few on lateral shoots. The clusters are called trusses and may have few or many blooms. They may be small or large and funnel-shaped, bell-shaped, tubular, or saucer-shaped, and double, semi-double, or hose-in-hose (one bloom in another) forms exist. Flower color is wide-ranging. The blooming period is dependent on the species or cultivar. Flowers can be produced from late winter to autumn, but most garden types flower from late winter to spring. The fruit is a capsule which splits to expel many small, dark seeds.
Classification is complex. Taxonomists have split the genus into several sub-genera as a result of intensive study, and changes to the nomenclatural status of Rhododendron continue to be made. For most gardeners, Rhododendron can be divided into five general types, large-leaved rhododendrons, small-leaved rhododendrons, vireya rhododendrons, evergreen azaleas and deciduous azaleas.
Rhododendron culture and use is species or cultivar dependent. It is best to match each plant’s growth requirements and site needs. Generally, most prefer indirect light and highly organic, acid soil. Most are shallow-rooted and require a combination of good drainage and even soil moisture, hence the need for lots of organic matter. Mulch plants well to conserve moisture and protect their roots. Many types develop buds in the summer for the following spring, so prune them shortly after they flower. Summer pruning can result in poor flowering the following year.
Rhododendron are beautiful in woodland gardens and look best planted in masses, especially in open forests. They are ideal for shaded foundations and borders and pair well with other Ericaceous ornamentals.
