Rhododendron calendulaceum
Common Name: flame azalea 
Type: Deciduous shrub
Family: Ericaceae
Native Range: Southeastern United States
Zone: 5 to 7
Height: 4.00 to 8.00 feet
Spread: 8.00 to 10.00 feet
Bloom Time: May to June
Bloom Description: Yellow to orange to red
Sun: Part shade
Water: Medium
Maintenance: Low
Suggested Use: Hedge
Flower: Showy
Attracts: Butterflies
Tolerate: Rabbit

Culture

Best grown in acidic, light, sandy, well-drained soils in part shade. Tolerates well-drained humusy loams. Does not prosper in areas with high summer temperatures, and is not recommended for planting south off USDA Zone 7. Prefers a sun dappled shade or high open part shade. Foliage may scorch in full sun unless soils are 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.

Noteworthy Characteristics

Rhododendron calendulaceum, commonly known as flame azalea, is an upright, loosely branched deciduous shrub that typically matures to 4-8' (infrequently to 10-15’) tall and to 8-10’ wide. It is native primarily to woodland slopes and mountain balds in the Appalachian Mountains from Pennsylvania to Georgia. Funnel-shaped, usually non-fragrant flowers (2” diameter) bloom in loose trusses (5-10 flowers per truss) in May-June. Flowers have exserted (protruding) showy stamens. Variable flower color ranges from yellow to orange to red. Medium green leaves (1-3” long) are elliptic to obovate with yellow-red fall color.

This species is an important parent of many deciduous azalea hybrids.

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 calendulaceus meaning orange-colored as are the flowers of Calendula.

Common name of flame azalea is in reference to the purported resemblance of the upright flower buds to candle flames.

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

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.