The majority of azaleas native to North America herald from Maine to Florida, running down the Appalachian mountain range. All of the North American natives are deciduous. They are known for their hardiness and exquisite fall foliage; many have sweet to spicy perfumes, and they tend to have an open, loosely branched habit.
Though azaleas, in general, prefer part sun and moist, humus-rich, well-drained soil, among species there is a broad spectrum of tolerance for heat, moisture and hardiness. Flowering times are also wide ranging: from early April into August.
Following are some native species and their cultivars that can be found in the Azalea Garden at The New York Botanical Garden.
In its native habitat, this low-growing (2 feet), stoloniferous (spreading, above-ground stems) azalea is found on dry hillsides and sandy coastal plains. When planted in rich garden soil, the suckering will be restricted and it will grow to 6 feet tall. The mid-May flowers are white with a yellow blotch and have an intense, spicy, lemon fragrance.
This large azalea averages 8 to 15 feet tall when mature. With a preference for well-drained, consistently moist soils, it is found on the banks of mountain streams. The flowers, which bloom from late June into July, are typically white with a striking red style and filaments (reproductive parts) that jump out at you. Its fragrance is reminiscent of heliotrope 'Cherry Pie' and its foliage turns red in fall.
Cultivars: R. ‘Hot Ginger and Dynamite’, R. ‘Pink Smokey’, R. ‘Summer Parasol’, R. ‘Sweet and Lowdown’
This low grower spreads along stolons and generally doesn’t get above 3 feet tall. It is native to the coastal plains from New Jersey to Georgia. White fragrant flowers are tinged with pink and appear in mid-May. It prefers moist soil and more sun than many azaleas, and is borderline hardy in New England.
Cultivars: R. ‘Milenberg Joys’, R. ‘The Pearls’
This azalea, hardy to Zone 6, grows 6 to 8 feet tall and produces fragrant, yellow-orange flowers in late April to early May. The flowers form dense clusters and range in color from shades of yellow to red, but are generally yellow-orange or orange-red. The shrub takes on a round habit when planted in sun and an upright habit when in part shade.
Cultivar: R. ‘Millie Mac’
This statuesque azalea can reach 12 feet in height. The color of its flowers speaks to its common name, with tones ranging from yellow to orange and red. Late-May to early-June blooms give way to red foliage in autumn.
A small upright grower, this azalea grows from 3 to 4 feet tall and has reddish-purple flowers that open in April. Its native range extends from Canada to Pennsylvania, making it suitable for cooler climates. It likes moist sites and does well in part shade.
A compact version of the flame azalea, this azalea reaches 3 to 8 feet tall and blooms two weeks later than the flame azalea (late June to July). The flowers of the Cumberland azalea are a deep reddish-orange in color.
Cultivar: R. ‘Camp’s Red’
Due to its heat and drought tolerance, this azalea is often hybridized with other species. Native from Georgia to South Carolina where it is found in open woods and on slopes, its late-May flowers range in color from yellow to orange-red. It generally reaches a height of 6 to 8 feet.
A woodland understory plant averaging 4 to 6 feet tall, the pinxterbloom fares better in heavier shade than most azaleas. Its slightly-fragrant, light- to dark-pink flowers open in late April to early May.
The pink flowers of this intensely fragrant, clove-scented azalea open in late May. Its bright-green foliage turns a yellow-bronze color in fall. Indigenous to open woods and stream banks from Quebec to Virginia and across to Missouri and Oklahoma, it is hardy in cold climates and grows 4 to 8 feet tall.
Cultivar: R. ‘Marie Hoffman’
This late bloomer has rich orange-red flowers that appear in mid- to late-July and glossy green foliage. It grows to 6 to 10 feet tall.
Cultivar: R. ‘Late Lady’
This azalea’s upright form averages 5 to 10 feet in height. Its pink flowers appear in early May, before the foliage, which turns red in fall. It is a high elevation species that can grow in rocky places.
Cultivars: R. ‘Pinkerbell’, R. ‘White Find’
This stoloniferous (spreading), hairy azalea is normally found in swamps or by fresh water ponds and averages 3 to 5 feet tall. Nicknamed swamp honeysuckle, its sticky, white flowers have a clove-like fragrance and bloom in June and July. It grows well in sun or shade and in wet conditions.
Cultivars: R. ‘Betty Cummins’, R. ‘Bob’s Bayou Beauty’, R. ‘Delaware Blue’, R. ‘Pink Mist’
Rhododendrons & azaleas : a colour guide by 
Rhododendrons and Azaleas by 
Success with Rhododendrons and Azaleas by 
The Timber Press Encyclopedia of Flowering Shrubs by 
