Rhododendron viscosum
Common Name: swamp azalea 
Type: Deciduous shrub
Family: Ericaceae
Native Range: Eastern and southern United States
Zone: 4 to 9
Height: 3.00 to 5.00 feet
Spread: 3.00 to 5.00 feet
Bloom Time: May to July
Bloom Description: White to pale pink
Sun: Part shade
Water: Medium to wet
Maintenance: Medium
Suggested Use: Hedge
Flower: Showy, Fragrant, Good Cut
Leaf: Good Fall
Attracts: Hummingbirds, Butterflies
Tolerate: Rabbit, Wet Soil

Culture

Best grown in acidic, humusy, well-drained loams in part shade. This species of azalea is tolerant of moist to wet soils including ones with somewhat poor drainage (its native habitat is swampy lowland areas). It also tolerates periodic flooding, but will not grow in soils where the roots are submerged in water. Root rot is less likely to occur with this species. Prefers a sun dappled shade or high open part shade. Foliage may scorch in full sun unless soils are kept uniformly moist. Roots must never be allowed to dry out. Acidify soils prior to planting and thereafter as needed. This azalea should never be planted near a black walnut or butternut tree (roots of both trees produce toxic juglones which will typically damage or kill rhododendrons/azaleas growing within or close to the drip line of either tree). It is best sited in a location protected from strong winter winds. This shrub has a shallow, fibrous root system (do not cultivate around the shrub) and will benefit from a good mulch (wood chips, bark or pine needles) for retention of moisture, stabilization of soil temperatures and winter protection. Clip off spent flower clusters immediately after bloom as practicable. Plants will slowly naturalize by root suckers.

Noteworthy Characteristics

Rhododendron viscosum, commonly known as swamp azalea, is a loose, upright-spreading, deciduous woody shrub that typically grows to 3-5' (less frequently to 8') tall. Branching opens up with age. It is one of 17 species of azalea which are native to the U.S. It is typically found in swamps, bogs, stream margins and wet lowlands from southwestern Maine to northeastern Ohio south to Florida and Alabama. It may be found at some higher elevations in the Appalachian Mountains. Fragrant (musky clove-like aroma), tubular, white to pale pink flowers (1 1/4" across) bloom in clusters of 4-9 after the leaves have emerged in May-July (one of the last of the native azaleas to flower). Each flower has 5 petal-like lobes. Narrow, obovate to oblong-ovate leaves (to 2 1/2" long) with wedge-shaped bases and blunt/short-pointed tips are clustered at the branch ends. Leaves are dark green above and pale green below. Leaves turn attractive shades of yellow, orange and purple in fall. Branchlets are hirsute (stiff hairs). Fruits are egg-shaped capsules (to 3/4" long).

Genus name comes from the Greek words rhodo meaning rose and dendron meaning tree. Transferred from the Greek name for Nerium oleander.

Specific epithet comes from the Latin word viscosus meaning sticky in reference to the sticky substance excreted by glandular hairs on the corolla tubes of the flowers.

Additional common names include clammy azalea in reference to its sticky (viscous) corolla tubes and honeysuckle azalea (even though it is a rhododendron and not a honeysuckle) in reference to the resemblance of its flowers in both appearance and fragrance to the flowers of some honeysuckles.

Problems

Azaleas are susceptible to many insect and disease problems, including but not limited to canker, crown rot, root rot, leaf spot, rust, powdery mildew, aphids, borers, lacebugs, leafhoppers, mealybugs, mites, nematodes, scale, thrips and whitefly. A healthy plant in the proper environment with proper care should have limited problems, however.

Garden Uses

Best grouped in shrub borders, mixed borders, open woodland gardens, native plant gardens and open shade gardens. Effective near patios or decks. Specimen around the home. Plants in groups with earlier blooming azaleas to extend the annual azalea bloom period. Plants often thrive when sited in moist soils near stationary or moving water. Good cut flower.