Common Name: rhododendron
Type: Broadleaf evergreen
Family: Ericaceae
Native Range: Caucasus, Turkey
Zone: 5 to 8
Height: 5.00 to 6.00 feet
Spread: 5.00 to 6.00 feet
Bloom Time: May
Bloom Description: Pale pink to rose purple
Sun: Part shade
Water: Medium
Maintenance: Medium
Suggested Use: Hedge
Flower: Showy
Leaf: Evergreen
Attracts: Hummingbirds, Butterflies
Other: Winter Interest
Tolerate: Rabbit
Culture
Best grown in acidic, light, sandy, well-drained soils in part shade. Tolerates well-drained humusy loams. Prefers a sun dappled shade or high open part shade. This species is native to cool mountain areas with exposure to some full sun, however foliage has less tolerance for full sun in hot summer climates particularly if soils are not kept uniformly moist. Consistent moisture is best, but soils must drain well (doesn’t like “wet feet”). Poor drainage inevitably leads to root rot, therefore raised beds/plantings should be considered in heavy clay soils such as those present in much of the St. Louis area. Roots must never be allowed to dry out. Acidify soils prior to planting and thereafter as needed. This shrub should be planted in a location protected from strong winter winds in the St. Louis area. Shallow, fibrous root systems (do not cultivate around shrubs) 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. Slowly naturalizes by root suckers.
Noteworthy Characteristics
Rhododendron smirnowii, commonly known as smirnow rhododendron, is an upright spreading broadleaf evergreen shrub that is native to pine/spruce forests up to and slightly above tree line in the Caucasus. Species plants are perhaps best known for having good winter hardiness, indumented foliage and frilled corollas (hybridizers have used this rhododendron as a parent to take advantage of the aforementioned characteristics). This shrub typically matures to 5-6' tall, but over time may rise to as much as 12' tall (to 20' tall in their native habitat). Pale pink to rose purple funnel-shaped flowers (2-3" across) with frilly pink margins bloom in May in rounded clusters (trusses of 9-12). This is a heavily indumented species (leaf undersides are covered with felted white to silvery hairs which often age to brownish-white or orange-brown or gray). Oblong to oblanceolate leaves (to 6" long) are covered with tomentum on top and indumentum below (tomentum/indumentum describes this covering of fine woolly hairs which protect the leaf from water loss and extreme temperatures). The tomentum on top found on new leaves gradually disappears as the summer progresses leaving a dark green leaf, but the indumentum below remains throughout the year. In subsequent years, this felty leaf coating on mature leaves is usually confined to the leaf undersides.
Genus name comes from the Greek words rhodo meaning rose and dendron meaning tree. Transferred from the Greek name for Nerium oleander.
Baron Ungern-Sternberg discovered this plant in 1885 in the Caucasian Mountains and named it after a friend, M. Smirnov, hence the specific epithet and common name.
Problems
Rhododendrons 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.
Uses
Group or specimen for shrub borders, mixed borders, open woodland gardens, native plant gardens and open shade gardens. Effective near patios and as a specimen around the home.