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Genus Rhododendron (Azalea)

Rhododendron schlippenbachii Photo/Illustration: Chris Curless

roe-doe-DEN-dron

Common Name: Azalea

Plants in this massive genus are grown mainly for their showy (sometimes fragrant) flowers, which come in numerous shapes, sizes, colors, and bloom times. The leaves, while not especially showy, offer some early or late season color and are evergreen in some species.
Noteworthy characteristics: Generally dark, lance-shaped leaves, some with fine hairs, some with bronze coloring, and some evergreen. Single or clusters of tubular flowers in many colors. Size ranges from low mat-forming shrubs to small trees.
Care: Grow in moist, fertile, humus-rich acidic soil (pH 4.5 to 5.5) in dappled shade. Plant shallow, as plants are surface rooted and like a mulch covering.
Propagation: Root semi-ripe cuttings in late summer or autumn. Layer in autumn.
Problems: Vine weevil, whitefly, leafhoppers, lacebugs, scale, caterpillars, aphids. Powdery mildew, rust, bud blast, leaf gall, petal blight, root rot, and chlorosis (due to insufficient soil acid).

Species, varieties and cultivars for genus Rhododendron

Rhododendron 'Admiral Semmes'
(Azalea) Be the first to rate this plant

Hardiness Zones:

This native azalea, winner of the 2007 Georgia Gold medal award, will thrive in heat and humidity, which is why it is a good choice for the South. Large, fragrant yellow blooms appear in early spring. Reportedly pest- and disease free, 'Admiral Semmes' is a progeny of Exbury hybrid R. 'Hotspur Yellow' and R. austrinum.

Rhododendron calendulaceum
(Flame azalea) Be the first to rate this plant

Hardiness Zones:

This plant's leaves are mid-green, and softly hairy on both sides. In late midseason, as leaves emerge or just after, this plant bears lax trusses of yellow to dark reddish orange flowers. It grows to 8 feet tall and wide.

Rhododendron canescens
(Florida pinxter, Hoary azalea, Piedmont azalea) Be the first to rate this plant

Hardiness Zones:

This narrow deciduous azalea bears fragrant, funnel-shaped, white, pink, or deep rose flowers. It grows to 15 feet tall and 5 to 6 feet wide. Mid-green leaves are densely hairy beneath.

Rhododendron prunifolium
(Plumleaf azalea) Be the first to rate this plant

Hardiness Zones:

This late-flowering azalea has bright red flowers over crisp green leaves in summer to autumn.

Rhododendron schlippenbachii
(Royal azalea) Be the first to rate this plant

Hardiness Zones:

Royal azalea has large, fragrant pink blooms in spring. This large-leaved azalea also has purple-hued foliage in spring, turning velvet green in summer, and finally fading to yellow in autumn.

Rhododendron vaseyi
(Pinkshell azalea) Be the first to rate this plant

Hardiness Zones:

This deciduous azalea bears trusses of 4 to 8 broadly funnel-shaped, unscented clear pink flowers in early mid-season. Blooms appear before the leaves emerge. Shiny, dark green leaves are paler green beneath.

Rhododendron viscosum and cvs.
(Swamp azalea, Sweet azalea) Be the first to rate this plant

Hardiness Zones:

This deciduous azalea has dark green leaves and funnel-shaped white flowers suffused with pink. The flowers have a spicy, sweet fragrance. This plant blooms very late in the season, and sporadically throughout the summer. Cultivars include 'Delaware Blue’, ‘Pink and Sweet’, 'Lemon Drop’, 'Parade’, and ‘Lollipop’.

Rhododendron williamsianum
(Williams rhododendron) Be the first to rate this plant

Hardiness Zones:

This rhododendron from China is quite unlike most of the better known species planted in gardens today. Its leaves are small, oval and, when young, bronze. Dainty-looking, pink, bell-shaped flowers bloom in spring. Williams rhododendron reaches just 5 feet tall and almost as wide, making it a nice choice for beds and borders in a shady area.