Azaleas are grouped together as one species of the genus Rhododendron are therefore members of the heath family (Ericaceae). This could cause some confusion, because of number of related plants referred to by the common name of rhododendron. This publication refers only to those plants which are true azaleas.
Botanically, azaleas are separated from rhododendron based upon floral structure. Azaleas have 5 to 7 stamens per flower, while rhododendrons have 7 to 10 stamens per flower. Currently, there are between 70 and 80 species of azaleas and several thousand cultivars. Our modern-day azaleas which nurserymen grow and sell can be a species or a hybrid. Species are grown from the native environment or possibly grown from seed collected from a particular cultivated plant. Hybrids are developed through a controlled breeding process and are propagated asexually and distributed as a specific variety or, more correctly, a cultivar. Thus, the Pinxterbloom Azalea or Wild Honeysuckle (R. nudiflorum) is a species while George L. Taber is a hybrid. Species will come true to type from seed while hybrids will not. The following is a simplified list of the more popular groups being grown in North Carolina.
Kurume Hybrids. This popular group of evergreen azaleas is generally thought of as dwarf or semi-dwarf in size. They range in height from 2 to 6 feet with a spread of 2 to 5 feet. Kurume azaleas have extremely dense foliage and twiggy branch structure. The hardiness zones are 6,7,8 and 9 with flowering periods in mid-spring.
The growth rate is considered to be moderate. The popular cultivars for North Carolina nurseries are as follows:
Southern Indica Hybrids. This group of azaleas, commonly referred to as Indica azaleas, are very popular in the eastern and southeastern parts of North Carolina because of their lack of cold hardiness. Indica azaleas grow to a height of 6 to 12 feet with a spread of 6 to 8 feet and flower from late March to mid to late April. The flowers can reach a diameter of 2 to 3 inches. Indica Azaleas are as follows:
Belgian Indian Hybrids. The Belgian hybrids were developed in Belgium and England from the hybridization of the Indian Hybrids in the mid-1980s. Developed mainly as greenhouse forcing varieties, this group is extremely tender and not recommended for landscape use. Several popular cultivars are as follows:
Indica Azaleas (R. indicum). The true R. indicum from Japan (1883) is a small, dense, semi-evergreen azalea rarely reaching 3 feet in height. Most of the common late-flowering cultivars (June) are sold as Macrantha' azaleas.
Dwarf Indica Azaleas (R. eriocarpum). Commonly known as the Gumpo' group, these are the most popular dwarf azaleas for North Carolina landscapers. These very low, dense, compact azaleas produce an abundance of blooms in June and even early July. Gumpo' produces white blooms with a 2 1/2- to 3-inch diameter flower and Pink Gumpo' is pale pink with a white edge.
Gable Hybrids. This large group of hybrids was developed by Joseph Gable in Pennsylvania and introduced in the mid 1920's. This very hardy group was obtained by crossing the Korean and Kaempferi azaleas. This group of hybrids is very popular in the western and northwestern parts of North Carolina. Popular varieties are as follows:
Satsuki Hybrids. The Satsukis were introduced from Japan to the U.S. in 1938. Satsuki azaleas generally are low growing, only reaching a height of 2 to 4 feet and a spread of 2 to 4 feet, flowering in May to June with large showy flowers. Colors vary quite widely, some being one color, striped or some with a different color margin.
Kaempferi Hybrids. This is a large group of azaleas which originated in Holland around 1920. They are popular because they are extremely cold hardy.
Glenn Dale Hybrids. This large group of hybrids have been developed since 1935 by B. Y. Morrison of the USDA at Glenn Dale, Maryland. They were developed to produce large and varied flowers like the Southern Indian Azaleas yet be much more cold hardy.
The flowering season was extended with the development of the Glenn Dale hybrids. Some flower as early as the Kurumes, in mid- March, while others don't flower until mid-June. Flowers can range to over 4 inches in diameter, single, hose-in-hose, semi-double and double. The general size would be 4 to 6 feet in height with a 3- to 4-foot spread. There are more than 450 named cultivars.
Pericat Hybrids. The Pericat hybrids were introduced as greenhouse-forcing azaleas in 1931. Some are as hardy as the Kurume, but most are rather tender. (They were crosses between the Kurume and Belgian Indian Azaleas.) For landscape purposes they should be used only in southern areas of North Carolina.
Carla Hybrids. Since the azalea breeding program was initiated in part, by a former North Carolina State horticulturist now at Louisiana State University, all resulting cultivars will be released as Carla (North Carolina/Louisiana) hybrids.
In July 1976, the North Carolina Agricultural Research Service approved the release of seven azalea cultivars: Adelaide Pope, Carror, Elaine, Emily, Jane Spalding, Pink Cloud, and Sunglow.
In 1982, the Agricultural Research Service approved the release of four additional Carla hybrids Autumn Sun, Cochran's Lavender, Pink Camellia, and Wolfpack Red.
The following are descriptions of the new azalea cultivars:
| Elaine | Flowers light pink, fully double, medium sized rose-bud- type opening full in later development, 1 to 3 flowers per bud; plant medium sized; bloom in Raleigh area April 16 to 26. |
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| Carror | Flowers rose pink, semi-double, medium sized, 1 to 4 per bud; plant medium sized, compact; blooms in Raleigh area April 25 to May 1. |
| Pink Cloud | Flowers light pink, predominately single, large-sized, 2 to 4 per bud; plants medium sized; blooms in Raleigh area April 15 to 25. |
| Jane Spalding | Flowers rose pink, single, 1 to 3 per bud, medium-sized; plants medium sized; blooms in Raleigh area April 15 to 25. |
| Emily | Flowers deep rose red, single, medium-small, 1 to 3 per bud, hose-in-hose; plant medium sized; compact; blooms in Raleigh area April 18 to 30. |
| Adelaide Pope | Flowers deep rose pink, single, medium-large, 1 to 5 per bud; plant medium large, vigorous, compact, blooms in Raleigh area April 15-to 25. |
| Sunglow | Flowers deep rose pink, single, medium large, 1 to 4 per bud; plant medium-large sized, vigorous; blooms in Raleigh area April 20 to 30. |
| Autumn Sun | Flowers bronze-red, hose-in-hose, medium small, 2 to 3 per bud; plant small to medium; upright-spreading, dense; blooms in Raleigh area April 15 to 25. |
| Cochran's Lavender | Flowers purplish pink, single, medium sized, 1 to 3 per bud; plant medium in size, spreading, dense, blooms in Raleigh April 15 to 25. |
| Pink Camellia | Flowers light purplish pink, completely double, rosebud tube opening full in later development, 1 to 3 flowers per bud; plant medium sized; blooms in Raleigh area April 15 to 25. |
| Wolfpack Red | Flowers strong red, single, small, 1 to 4 flowers per bud; plant semi-dwarf, spreading; blooms in Raleigh area April 15 to 25. |
Native Azaleas. Deciduous native azaleas are found throughout North Carolina along the coast to the Appalachian range. Native azaleas include the Florida azalea (R. austrinum), Cumberland azalea (R. bakeri), Flame azalea (R. calendulaceum), and Plum leaf azalea (R. prunifolium). Those native species generally have orange or red flowers. Native Pink Azaleas include the Florida Pinxter Azalea (R. canescens), Pinxterbloom Azalea (R. nudiflorum), Roseshell Azalea (R. roseum), and Pinkshell Azalea (R. vaseyi).
White flowering azaleas include the Sweet Azalea (R. aborescens), Texas Azalea (R. oblongifolium), Swamp Azalea (R. viscosum), and Dwarf Azalea (R. atlanticum).
Several hybrid azaleas were developed from crosses between two or more of the deciduous native species. The most popular being the Ghent hybrids (1830) and the Mollis hybrids (1870).
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