Rhododendron calendulaceum (Flame Azalea)

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Rhododendron calendulaceum

flame azalea

Ericaceae

Appalachian Mountains, eastern United States

Attracts Pollinators Attracts Butterflies Attracts Hummingbirds Container Friendly

Native to North America

SunFull Sun – Part Shade

WaterMedium

HardinessZones 5–7

Overview

Rhododendron calendulaceum is a deciduous azalea native to the Appalachian Mountains, reaching 4-10 feet (1.2-3 m) tall and about as wide with an upright, open, loosely branched form. Oval leaves 1.5-3 inches (3.8-7.6 cm) long are medium green and softly hairy, clustered at the branch tips, turning yellow to bronze in fall before dropping. In late spring, clusters of funnel-shaped flowers 1.5-2 inches (3.8-5 cm) across open as or just before the leaves expand, ranging from yellow and gold through orange to red, with a long flaring tube and protruding stamens. The flowers carry little or no scent. Seed capsules follow and split to release tiny seed. It is hardy in USDA zones 5-7 and grows on cool, acidic, well-drained mountain soils high in organic matter. The shallow roots dry out quickly in heat, and the species struggles in hot, humid lowlands and in alkaline soil.

Native Range

Rhododendron calendulaceum is native to the southern and central Appalachian Mountains of the eastern United States, from Pennsylvania and West Virginia south to Georgia and Alabama. It grows in open woods, dry ridges, balds, and forest edges from about 1,500 to 5,500 feet (450 to 1,700 m).

Suggested Uses

Used in woodland and native plant gardens, on shaded slopes, and in naturalistic shrub borders with other acid-soil plants such as mountain laurel and blueberries. The late-spring flowers draw butterflies and other pollinators.

How to Identify

Identify flame azalea by its deciduous habit and its clusters of funnel-shaped flowers in yellow, orange, or red with a long tube and protruding stamens, opening in late spring as the leaves expand. The flower color range and the soft-hairy oval leaves separate it from the pink-flowered R. periclymenoides. The flowers lack the strong scent of some other native azaleas.

Appearance

Size & Dimensions

Height4' - 10'

Width/Spread4' - 10'

Reaches mature size in approximately 8 years

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~3 weeks

Spring

Flowering runs from April through June, varying with elevation, as the new leaves emerge. Each cluster holds five to seven funnel-shaped flowers in shades from yellow through orange to red. Bees, butterflies, and swallowtails in particular work the flowers for nectar.

Detailed Descriptions

Flower Description

yellow to orange to red

Foliage Description

medium green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 4-8 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range4.5 - 6.0(Acidic)

357912

Soil Types

loam peat sand

Drainagewell drained

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Time to Maturity

5-10 years

Care & Maintenance

Care Guide

Grows in part shade to full sun on cool, moist, acidic, well-drained soils high in organic matter. A soil pH of 4.5-6.0 is needed, and the shrub develops chlorosis in alkaline ground. Shallow roots call for steady moisture and a mulch of leaf litter or bark, especially in sun. Afternoon shade in hot regions reduces heat stress on the foliage and roots. The plant does poorly in heavy clay, wet ground, or hot, humid lowlands. No heavy feeding is needed in suitable woodland soil.

Pruning

Pruning just after flowering removes spent trusses and shapes the open form before next year buds set. Dead or crossing stems can be taken out at the same time. Hard cutting into old wood regrows slowly on this species.

Pruning Schedule

late spring