As one travels across North Carolina it is quite evident that azaleas are favorite ornamental plants for home gardeners and professional landscapers. Azaleas offer a wide range of size, form and color, and can be used as specimen plant accents or as a mass planting. Flowering dates are from late March to late June with both ever-green and deciduous types avail-able. Azaleas can be grown all across the state (Zones 6,7,8,9), but in order for these shrubs to grow, mature, flower profusely, and generally contribute to the total landscape, an understanding of the different kinds of azaleas, the culture, and environmental factors is necessary.
Azaleas are grouped together as one species of the genus Rhododendron, and are therefore members of the Heath Family (Ericaceae). This could cause some confusion because of the 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. There is obviously a great deal of confusion with classifying azaleas. The following is a simplified, short breakdown of the more popular groups being grown in N.C.
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 N.C. nurseries are:
Southern Indica Hybrids - This group of azaleas, commonly referred to as Indica azaleas, are very popular in the eastern and southeastern parts of N.C. 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. They are popular cultivars of the South. Indica Azaleas are as follows:
Belgian Indican Hybrids - The Belgian hybrids were developed from the hybridization of the Indican Hybrids, in Belgium and England in the mid 1980's. Developed mainly as greenhouse forcing varieties, this group is extremely tender and not recommended for landscape use. Several popular cultivars are:
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 N.C. gardeners. These very low, dense, compact azaleas produce an abundance of blooms in June and even early July. 'Gumpo' produces white blooms with a 2½- 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 among gardeners in the western and northwestern parts of N.C. Popular varieties are:
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 dates would be 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 Indican Azaleas yet be much more cold hardy. 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. 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. There are over 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 Indican Azaleas.) For landscape purposes they should be used only in southern areas of N.C.
Carla Hybrids - Since the azalea breeding program was initiated in part by a former N.C. State horticulturist now at L.S.U., all resulting cultivars will be released as Carla (North Carolina - Louisiana) hybrids.
In July 1976, the N.C. 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 wide in later development, 1 to 3 flowers per bud; plant medium sized; bloom in Raleigh area April 16-26.
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 15-25.
Jane Spalding - Flowers rose pink, single, 1 to 3 per bud, medium sized; plants medium sized; blooms in Raleigh area April 15-25.
Emily - Flowers deep rose red, single, medium to small, 1 to 3 per bud, hose-in-hose (one flower within another); plant medium sized; compact; blooms in Raleigh area April 18-30.
Adelaide Pope - Flowers deep rose pink, single, medium to large, 1 to 5 per bud; plant medium large, vigorous, compact, blooms in Raleigh area April 15-25.
Sunglow - Flowers deep rose pink, single, medium large, 1 to 4 per bud; plant medium to large sized, vigorous; blooms in Raleigh area April 20-30.
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 15-25.
Cochran's Lavender - Flowers purplish pink, single, medium sized, 1 to 3 per bud; plant medium in size, spreading, dense, blooms in Raleigh April 15-25.
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 15-25.
Wolfpack Red - Flowers strong red, single, small, 1 to 4 flowers per bud; plant semi-dwarf, spreading; blooms in Raleigh area April 15-25.
Native Azaleas - Deciduous native azaleas are found throughout N.C. along the coast to the Appalachian range. Native azaleas would include the Florida azalea (R. austrinum), Cumberland azalea (R. bakeri), Flame azalea (R. calendulaceum), Plum leaf azalea (R. prunifolium). Those native species generally have orange or red flowers. Native Pink Azaleas would include the Florida Pinxter Azalea (R. canescens), Pinxterbloom Azalea (R. nudiflorum), Roseshell Azalea (R. roseum), and Pinkshell Azalea (R. vaseyi).
White flowering azaleas would include the Sweet Azalea (R. aborescens), Texas Azalea (R. oblongifolium), the Swamp Azalea (R. viscosum), and Dwarf Azalea (R. atlanticum).
Several hybrid azaleas were developed from crosses between 2 or more of the deciduous native species, the most popular being the Ghent hybrids (1830) and the Mollis hybrids (1870).
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.