Selecting and Growing Azaleas (B 670) University of Georgia Extension Azaleas' vivid colors, profusion of flowers and adaptability to a wide range of soils and climates make them one of the most popular flowering shrubs in Georgia. Although most people associate azaleas with spring, there are several that bloom in summer and fall. By carefully selecting plants, you can have azaleas blooming at least eight months of the year. 2017-03-27 15:24:42.717 2007-10-22 15:14:53.0 https://secure.caes.uga.edu/extension/publications/images/primary-pub-images/B670-primary.jpg Selecting and Growing Azaleas | Publications | UGA Extension Skip to content

Selecting and Growing Azaleas (B 670)

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azaleas

Gary L. Wade, Ph.D., Extension Horticulturist
S. Kristine Braman, Ph.D. Entomologist
Jean Williams Woodward, Ph.D., Extension Plant Pathologist
in cooperation with
Frank Bryan, Ph.D., Jim Thornton and Albert Penland, Oconee Chapter, Azalea Society of America

Introduction

Few plants can rival the spectacular floral displays of azaleas. Their vivid colors, profusion of flowers, and adaptability to a wide range of soils and climates make them one of the most popular flowering shrubs in Georgia. Although most people associate azaleas with spring, several bloom in summer and fall. By carefully selecting plants, you can have azaleas blooming at least eight months of the year.

Botanically, azaleas are members of the Ericaceae (Heath) family, which includes blueberries and mountain laurel. All azaleas are rhododendrons, and both are in the genus Rhododendron. The term “rhododendron,” however, is commonly used to refer to the group of plants usually with large, leathery, evergreen foliage, while “azalea” refers to those with smaller, thinner leaves. Generally, azaleas and rhododendrons have the same cultural requirements.

The Royal Horticultural Society in London maintains an International Rhododendron Registry that lists over 800 species and several hundred named cultivars. To be registered, a cultivar must have a unique name and unique characteristics that set it apart from others. Some hybridizers in the United States register their new cultivars with the Rhododendron Society of America.

Grouping Azaleas by Characteristics

Azaleas are grouped into categories based on a number of plant characteristics, including whether they are evergreen or deciduous (shed their foliage in winter), and whether they are a native plant species or an introduced cultivar. Evergreen azaleas are described according to flower form, petal shape, variation in petal colors, plant size, time of bloom and growth habit. Many hybrid evergreen cultivars are grouped according to the name of the plant breeder who introduced them or the location where they were developed. These various groups and characteristics are described below.

Evergreen vs. Deciduous

Evergreen azaleas maintain some of their leaves throughout the year, while deciduous azaleas lose their leaves in autumn.

Most evergreen azaleas originated in Japan, but some came from China, Korea or Taiwan. Several deciduous azaleas are native to North America; others originated in Eastern Europe, Japan, China and Korea. Others come from hybrid crosses.

Flower Forms and Petal Shapes

Parts of a flower drawing.Figure 1. Parts of a flower.

Azaleas are often described according to the shape or form of their flower. In order to understand the terminology used to describe flower forms, it is helpful to review the parts of a flower (Figure 1). The stigma, style and ovary make up the female part of the flower. These three parts are collectively called the pistil. The male part of the flower includes the anthers and filament, which make up the stamen. The petals are the showy part of the flower. Below the petals are the sepals. In some flowers, the sepals are green and leaf-like, while in others they are colored like petals.

illustration of single, semi-double, doubl, single hose-in-hose, semi-double-hose-in-hose, and double hose-in-hose flower formsFigure 2. Flower forms.

Deciduous azaleas typically have tubular flowers with long stamens that extend beyond their petals. Evergreen azaleas, on the other hand, may have a wide variety of flower forms. Figure 2 shows six flower forms used to describe the flowers of evergreen azaleas.

Single flowers consist of five or more petals with five to ten stamens and a single pistil. This is the most common flower form. Semi-double flowers have had some stamens transformed into petals. Double flowers have had all their stamens transformed into petals. Hose-in-hose types consist of two flower forms that appear to be inserted into one another; the top flower is derived from the petals and a lower flower consists of colored sepals. Then there are semi-double hose-in-hose types, which combine the features of semi-double and hose-in-hose forms, and double hose-in-hose types, which combine the features of double and hose-in-hose forms. Hose-in-hose and double flower forms tend to hold their blossoms after flowering. The blossoms turn brown and wither on the plant instead of dropping off.

Azaleas also may have a wide variety of petal shapes, including strap-like petals, star-shaped petals, spider-like petals or round petals. Petals may be one solid color, or they may be flecked or bordered in a different color.

Figures 3a-3h. Petal shapes and color variations.

Strap like flower petals3a. Strap-like
Photo: Richard Clapp
Star-shaped flower petals3b. Star-shaped
Photo: Richard Clapp
Spider-like flower petals3c. Spider-like
Photo: Frank Bryan

round petal flower petals3d. Round petal
Photo: Frank Bryan
Red self flower petals3e. Red self
Photo: Frank Bryan
Sectored flower petals3f. Sectored
Photo: Frank Bryan

Margins/borders flower petals3g. Margins/borders
Photo: Allison Fuqua
Flecked and/or striped flower petals3h. Flecked and/or striped
Photo: Georgia Cooperative Extension

Another way azaleas are grouped is whether they bloom early, mid-season or late. Early flowering types generally bloom from mid-February through March, mid-season types bloom in late April and May, and late-flowering types bloom from June through October.

Native vs. Introduced Cultivars and Hybrids

Native Azaleas

Several species of azaleas are native to Georgia and the Southeast. Their flower color ranges from white to pink, yellow, orange, scarlet or crimson, with several shades in between. Plant size is also variable, ranging from 3 feet to more than 20 feet. Although native azaleas are considered more adaptable and more hardy than introduced species, it is important to approximate their native growing environment if they are to be grown successfully.

The following are some native azalea species found in Georgia:

Alabama azalea white flowersAlabama azalea,
R. alabamense
Photo: Frank Brya

Alabama Azalea, R. alabamense [ah-luh-ba-MEN-see] bears white flowers with a yellow blotch. It has a lemony-spice fragrance. This low to medium size shrub grows in Alabama and western Georgia.


Piedmont azalea light pink flowersPiedmont azalea,
R. canescens

Photo: Frank Bryan

Piedmont Azalea, R. canescens [kuh-NES-enz] has white to pinkish tubular flowers with stamens two to three times longer than the petals. This tall-growing plant may attain a height of 15 feet. Some have flowers with a musky-sweet, honeysuckle-like fragrance. As the common name implies, the Piedmont Azalea is native to the Piedmont region of Georgia and other states.


Flame azalea red flowersFlame azalea,
R. calendulaceum

Photo: Frank Bryan

Flame Azalea, R. calendulaceum [kuh-len-dew-LAY-see-um] has flower colors ranging from brilliant shades of yellow to orange or red, with a large prominent yellow to orange blotch on the upper lobe (petal). Its flowers tend to be larger than the other native species. Flame azalea is native from the Appalachian Mountains to the Piedmont region.


Sweet or Smooth azalea pinkish-white flowersSweet or Smooth azalea,
R. arborescens

Photo: Frank Bryan

Sweet or Smooth Azalea, R. arborescens [ar-bo-RES-enz] has white flowers, sometimes with a pinkish tinge, and red stamens. It has glossy leaves and red fall foliage. Flowers have a strong, cinnamon-like fragrance. This species is native to west-central Georgia. It may attain a height of 8 feet.


Coastal or Dwarf azalea white flowersCoastal or Dwarf azalea,
R. atlanticum
Photo: Richard Clapp

Coastal or Dwarf Azalea, R. atlanticum [at-LAN-tih-kum] has white flowers that sometimes are flushed with pink. The plant grows 3 to 5 feet tall and is smaller than most of the other native species. It is native to the Coastal Plain from Pennsylvania to Georgia. Flowers have a rose-like fragrance.


Pinxterbloom azalea pink flowersPinxterbloom azalea,
R. periclymenoides
Photo: Frank Bryan

Pinxterbloom Azalea, R. periclymenoides [pair-ih-kly-men-NOY-deez], previously classified as R. nudiforum, has narrow, wavy flowers that are either white, pale pink or deep pink. It is native from the Appalachian Mountains to the Piedmont and Coastal Plain.


Swamp azalea whitte flowersSwamp azalea,
R. viscosum
Photo: Richard Clapp

Swamp Azalea, R. viscosum [viss-KO-sum] has white to pink flowers that have a spicy, clover-like fragrance. The plant is variable in size and usually grows in low areas along stream banks from Maine to Georgia and west to Texas.


Florida azalea orange flowersFlorida azalea,
R. austrinum
Photo: Frank Bryan

Florida Azalea, R. austrinum [aw-STRY-num] has yellow to orange flowers with a reddish tube. Some plants have a lemony fragrance. This tall-growing species can be found in Florida and the Georgia-Alabama Coastal Plain.


Cumberland azalea red flowersCumberland azalea,
R. cumberlandense
Photo: Richard Clapp

Cumberland Azalea, R. cumberlandense [kum-bur-lan-DEN-see], previously classified as R. bakeri, has bright orange-red flowers. Plant height varies from 1 foot up to 6 feet. It can be found from the Kentucky-Tennessee-Cumberland plateau to the mountains of north Georgia.


Oconee azalea orange-red flowersOconee azalea,
R. flammeum
Photo: Richard Clapp

Oconee Azalea, R. flammeum [FLAM-ee-um], previously classified as R. speciosum, has yellow, yellow-orange or red flowers with a large yellow blotch on the top lobe (petal). This species is native to low elevations in open woods and on slopes across central Georgia.


Plumleaf azalea red flowersPlumleaf azalea,
R. prunifolium
Photo: Frank Bryan

Plumleaf Azalea, R. prunifolium [prew-nih-FO-lee-um] has flowers that range in color from apricot to orange or red. The petals have a deep red blotch. Plants are usually 5 to 8 feet tall, although some mature plants may attain a height of 20 feet. Plumleaf Azalea is native to a small region in southwest Georgia and eastern Alabama. It is the signature plant of Callaway Gardens in Pine Mountain, Georgia.


Deciduous Hybrids

Native azaleas have been crossed to produce many colorful, deciduous hybrid cultivars. These include ‘Exbury,’ ‘Knap Hill,’ ‘Ghent’ and related hybrid groups developed in England and Belgium. Because of their native-azalea parentage, several hybrids are fragrant. Most of these, however, do not grow well in Georgia, where the climate is hot and drought is common.

Selected forms and crosses of native azaleas have been made at Transplant Nursery in Lavonia, Georgia, and by the late Fred Galle at Callaway Gardens in Pine Mountain, Georgia. Crosses of the English cultivars with the native Florida azalea have been made by Dr. Eugene Aromi and at Dodd and Dodd Nursery in Mobile, Alabama. These hybrids have outstanding colorful blooms, and they can withstand hot weather. Among the adapted selections is ‘Gibraltar,’ a Knap Hill deciduous hybrid that performs better in central Georgia than most English and Belgian deciduous cultivars. It has fragrant, frilled, crimson-orange flowers in a ball-shaped cluster. ‘Red Pepper’ (vivid red flowers) is an example of a heat-tolerant Aromi cross. ‘Stonewall Jackson’ and ‘Admiral Semmes’ are examples of heat-tolerant Tom Dodd crosses.

Gibralter red flowers'Gibralter,'
a Knap Hill Hybrid.
Photo: Frank Bryan
Stonewall Jackson redish-orange flowers'Stonewall Jackson,'
a Tom Dodd Hybrid.
Photo: Frank Bryan
Admiral Semmes yellow flowers'Admiral Semmes,'
a Tom Dodd Hybrid.
Photo: Frank Bryan

Introduced (Non-native) and Hybrid Evergreen Azaleas

Dr. Fred Galle, former Director of Horticulture at Callaway Gardens in Pine Mountain, Ga., described more than 70 hybrid groups of evergreen azaleas in his book on azaleas (See “Suggested References”), and many more have evolved since then. Some of the major hybrid groups are described below.

Coral Bells pink flowers'Coral Bells,'
a Kurume Hybrid.
Photo: Allison Fuqua

Kurume Hybrids: Kurume azaleas are one of the most commonly grown azaleas in Georgia. They were imported from Kurume, Japan, to the Arnold Arboretum in Boston in the early 1900s and soon made their way into the nursery trade. Most Kurume hybrids are low- to medium-growing shrubs (2 to 3 feet), but a few grow to 5 to 6 feet.

Flowers are small but quite numerous, often masking the foliage. Colors range from white to pink, salmon or red, and some are bicolored. Most are cold hardy throughout Georgia. Popular Kurume hybrids include ‘Hinode Giri’ (rose-red flowers), ‘Coral Bells’ (soft pink flowers), and ‘Snow’ (white flowers).

George Lindley Tabor white with purplish-pink flower'George Lindley Tabor,'
a Southern Indian Hybrid.
Photo: Frank Bryan

Southern Indian Hybrids: Southern Indian (also called Southern Indica) hybrids were developed from plants at Magnolia Plantation in Charleston, S.C., and therefore are well adapted to the southern and coastal regions of Georgia. They are not reliably cold hardy in the northern half of Georgia, however. Most Southern Indian azaleas are fast growing and become quite large (5 to 8 feet tall and 5 to 10 feet wide), making them undesirable for foundation plantings. In south Georgia, they are often planted under pine trees, where they have filtered shade and plenty of room to grow.

Most Southern Indian hybrids bloom after the Kurume hybrids. Popular cultivars include ‘Formosa’(deep magenta-purple flowers), ‘George Lindley Tabor’ (white flowers with purplish-pink blotch and purple throat), and ‘Delaware Valley White’ (pure white flowers with ruffled petals).

Cinderella white striped with red flowers'Cinderella,'
a Glenn Dale Hybrid.
Photo: Frank Bryan

Glenn Dale Hybrids: Glenn Dale hybrids were developed by B.Y. Morrison at the U.S. Department of Agriculture Plant Introduction Station in Glen Dale, Maryland. More than 450 cultivars were hybridized from variable parentage. They are cold hardy to -10 degrees F and have a wide range of bloom times, flower colors, flower forms and plant growth habits. Many are not widely available in the trade, but their unusual flower colors and combinations of colors make them appealing. Interesting cultivars include ‘Zulu’ (vivid purple flowers with dark blotch), ‘Cinderella’ (white and red flowers or white striped with red), ‘Ambrosia’ (deep yellow-pink flowers), and ‘Sagittarius’ (vivid pink flowers with orange undertones).

Marian Lee white flowers with a tint of pink and red border'Marian Lee,'
a Back Acre Hybrid.
Photo: Richard Clapp

Back Acre Hybrids: Back Acre hybrid hybrids were also developed by B. Y. Morrison after his retirement to Pass Christian, Mississippi, in 1964, where he continued his azalea breeding work on his farm called Back Acres. More than 50 Back Acre cultivars resulted from his crosses. Plants have a wide array of flower colors and unusual color combinations, and many have frilled or double flowers. Examples are ‘Marian Lee’ (white petals with a tint of pink and carmen-red border), ‘May Blaine’ (light purple double flowers), and ‘Debonair’(vivid pink flowers with deep pink edges and light pink to greenish centers).

Nancy of Robin Hill light pink flowers'Nancy of Robin Hill,'
a Robin Hill Hybrid.
Photo: Richard Clapp

Robin Hill Hybrids: Robin Hill hybrids were developed in New Jersey, so they are cold hardy throughout Georgia. This group, consisting of 69 cultivars, is noted for having attractive foliage and large flowers that offer a spectrum of colors and color blends, many with soft pastel hues. Robin Hill azaleas bloom late and thrive in either sunny or semi-shady locations. Most plants are low growing (2 to 3 feet). Cultivars include ‘Nancy of Robin Hill’ (pastel-pink semi-double hose-in-hose flowers), ‘Olga Niblett’ (white flowers with yellow-green throat), and ‘Conversation Piece’ (white to purple-pink flowers having wavy edges).

Anna Kehr hot pink flower'Anna Kehr,'
an August Kehr Hybrid.
Photo: Richard Clapp

August Kehr Hybrids: Dr. August Kehr, former geneticist with the U.S. Department of Agriculture, developed some spectacular azalea cultivars having double or semi-double camellia-like flowers. Cultivars include ‘Anna Kehr’ (double rosey-pink flowers with wavy edges), ‘Mary Lou Kehr’ (light pink, semi-double fragrant flowers), ‘Great Expectations’ (reddish-orange double flowers), and ‘White Rosebud’ (white double flowers with yellow-green center). The plants are hardy to 0 degrees F.


Rosebud purplish-pink flowers'Rosebud,'
a Gale Hybrid.
Photo: Allison Fuqua

Gable hybrids: Gable hybrids were introduced by the late Joseph B. Gable, a nurseryman and hybridizer in Stewartstown, Pennsylvania. They are among the hardiest evergreen azaleas, adaptable to hardiness zone 6b (to -5 degrees F). They bloom mid-season and have a dense, spreading growth habit and medium height (5 to 6 feet). Several cultivars have double, hose-in-hose flowers that look like roses. The cultivar ‘Rosebud,’ for instance, has purplish-pink double rose-like flowers. Other cultivars include ‘Big Joe’ (purplish-pink flowers having a brown blotch), ‘Elizabeth Gable’ (deep red flowers with frilled edges), and ‘Polaris’ (white hose-in-hose flowers with greenish throat).

Janet Rhea fuchsia flowers with white edges'Janet Rhea,'
a Linwood Hybrid.
Photo: Richard Clapp

Linwood Hybrids: Linwood hybrids were developed for greenhouse forcing and the florist trade. Flowers are double and semi-double, and most are hose-in-hose types, 1½ to 2½ inches across. Plants are generally low-growing. Many are hardy to 0 degrees F. Examples are ‘Linwood Lavender’ (vivid purple flowers, semi-double and hose-in-hose form), ‘Janet Rhea’ (strong fuchsia-colored flowers with white edges, semi-double, hose-in-hose form), and ‘Hardy Gardenia’ (double white flowers with hose-in-hose form).