Deciduous Azaleas

Azaleas are members of the rhododendron genus. The basic difference is that azalea flowers have five pollen-bearing stamen while rhododendrons have 10 or more. The exceptions are R. canadense and R. vaseyi which have from 7 to 10 stamen. Azaleas are among the most colorful of all flowering shrubs, bearing 3- to 6-inch clusters of red, yellow, orange, pink, white or purple flowers in spring and early summer, and in many cases providing brilliantly hued leaves in fall. Many of the deciduous species described here allow gardeners in Northern regions to enjoy the beauty of this genus; they are not to be confused with evergreen azaleas that are widely grown from Zone 6 south. Many nursery catalogues list azaleas separately from the related plants commonly called rhododendrons, but both belong to a single genus, Rhododendron. Azaleas will serve most garden uses admirably, and they also can be grown in open woodlands in light shade where, with proper initial soil preparation, they are often able to take care of themselves indefinitely.

Deciduous azaleas are in the Pentanthera subgenus of Rhododendron. Most used in landscaping are hybrids of two, but usually more, Rhododendron species. Many of the species used in hybridization are native to eastern North American with additional species from Japan or Europe. Successful hybridization of deciduous azaleas was initiated in the 1820's by a Belgian baker living in Ghent. The plants from this series are known as the Ghent Azaleas. Many other series (types) of hybrid deciduous azaleas were developed in the 1800's and new ones continue to be released. [Return to Top]

Hybrid Deciduous Azaleas

Ghent azaleas are hybrids developed in Belgium about 150 years ago resulting from crosses between several American azalea species and R. luteum. Their single flowers, with one ring of petals, or double flowers, with numerous overlapping petals, are 1 1/2 to 2 inches across and come in white and in shades of yellow, orange, pink and red. They are hardy in Zone 5 to -10° F.

Knap Hill Hybrids (Exbury, Knap Hill and Slocock Hybrid azaleas) are exceptional hybrids developed at an English nursery of that name, but the term is also applied to the superb Exbury Hybrids, sometimes called de Rothschild Hybrids, bred at the de Rothschild estate in Exbury, Hampshire, England, as well as the Slocock Hybrids grown at the Slocock nursery in England. All these plants have individual flowers as large as 3 inches across, in great clusters of up to 18 flowers to a head. Basic colors are yellow, pink, red and white, but nearly every flower has at least two colors. The shrubs blossom in early summer, and the foliage usually turns yellow, orange or red in fall. Plants grow about 4 to 5 feet tall. Exbury and Knap Hill Strains are the ones usually offered by nurserymen in the USA. The Knap Hill hybrids are hardy in Zones 5-8, to -10° F. The foliage turns red, orange or yellow in autumn.

Maid in the Shade azaleas. Most deciduous azaleas do well in full sun and frequently are poor bloomers in the shade. "Maid in the Shade" deciduous azaleas is a collection of deciduous azaleas compiled by Transplant Nursery selected to do well in shadier locations. They include:

Mollis Hybrid azaleas, derived mainly from R. japonicum (syn. R. mollis var. japonicum), bear large clusters of 2- to 3-inch flowers in late spring. The colors include many shades of yellow, orange and pink as well as white. Plants usually grow about 5 feet tall and are hardy in Zone 5 to -10° F.

The Northern Lights are a new group of deciduous azaleas from the University of Minnesota for areas where winter temperatures are severe. They are a group of beautiful shrubs that are cold hardy to zone 3 and flower bud hardy to -40 °F. Plants are fairly compact and can grow to about 6 feet in height and width. Some of the more notable Northern Lights azaleas are:

Deciduous Azalea Species

R. arborescens, the sweet or smooth azalea, grows 4 to 6 feet tall and bears clusters of very fragrant 2-inch white or rose-tinged flowers in midsummer. Its leaves turn a deep glossy red in autumn and is hardy in Zone 5 to -15° F. [Return to Top]

R. atlanticum, the Atlantic Azalea or Coastal Azalea, is a low deciduous azalea found on coastal plains from Pennsylvania and Delaware south to Georgia. It is a good late flowering, scented species that can be used in cultivation. It is a common understory plant along the south eastern coastal plains of the United States. The white flowers are 1 to 1.5 inches across, but are often blushed with pink on the outside and some have a yellow blotch. Collected by John Clayton in 1743, this plant was appreciated more in England than in its native land. The plant habit is relatively low but stoloniferous. Spreading by underground stems, R. atlanticum can develop into very large colonies of an acre or more in sandy soils. R. atlanticum is easy to propagate, and makes a nice landscape plant in heavier soils which will restrict the spreading habit. [Return to Top]

R. calendulaceum, the flame azalea, is one of the most brightly colored of native North American shrubs, bearing large clusters of 2-inch flowers in early summer. Plants usually grow 4 to 9 feet tall in Zones 5-8, hardy to -10° F, and occasionally reach 15 feet. It bears clusters of 2-inch clove-scented bright scarlet, orange or yellow flowers in late spring or early summer flowers that are long lasting, even in full sun. The leaves are 3 inches long and drop in the fall. [Return to Top]

R. camtschaticum formerly called Therorhodion camtschaticum is a deciduous elepidote rhododendron found from Northern Japan to Alaska. This low growing rhododendron has the unusual trait that the one to three flowers appear at the end of young leafy shoots of the current year, and not from special buds. It does well in cultivation in alpine regions of Northern Germany and Eastern Scotland. It is difficult to grow in warmer climates. It was first described in 1784 by Pall. [Return to Top]

R. canadense, the Rhodora Azalea, is a low deciduous azalea found from Eastern Quebec to Newfoundland and Nova Scotia, and south the northern parts of Pennsylvania and New Jersey. It has showy lavender flowers. It has a white form that comes true from seed. It does well in moist acidic soils. Rhododendron canadense is a very unusual native azalea species and was originally considered an entirely separate genus, Rhodora . The top three petals of the flower are fused together almost to the end to form a single lobe, whereas the bottom two are completely separate lips. The purplish pink blossoms are approximately 1.5 inches across and have 10 stamens, twice the number of most east coast natives. First described by Linnaeus in 1762, R. canadense is a low stoloniferous shrub that is the most northern of the east coast native azaleas, the species is very cold hardy but a difficult plant where summers are hot and dry. [Return to Top]

R. canescens, the Florida Pinxter or Piedmont Azalea, is often confused with R. periclymenoides. Both are medium deciduous azaleas that are found in the Carolinas but can be separated by the flower tubes, which in R. periclymenoidesare fuzzy. R. canescens also has tiny hairs, but they are sticky and glandular. Another noticeable difference is that when a flower of R. periclymenoides dies, a ridge on the corolla tube tends to catch on the end of the pistil so that a flower cluster past its prime consists of several dangling blossoms. Although widespread in the eastern half of the U.S., these two wild azaleas differ in distribution. In South Carolina, for example, R. periclymenoides is a Piedmont plant, with almost no specimens reported from the Sandhills or Coastal plain, while R. canescens is predominantly a Low Country plant absent from the Piedmont, except in counties that border the Savannah River. In general, if it grows wild north of South Carolina, it's likely R. periclymenoides; south of the Palmetto State and it's probably R. canescens. Both species prefer moist, humus-laden, acidic soil but seem to do equally well in shade or sun. Old specimens can reach heights of 12-15 feet and have multiple stems or trunks up to 5" in diameter. [Return to Top]

R. colemanii, the Red Hills azalea, from the upper Coastal Plain of Alabama and Western Georgia, was named in 2008. It was initially collected and propagated by S. D. Coleman, Sr. It is one of the tallest, most fragrant and most richly colored of all the native azaleas. Different plants may show flower colors ranging from pure white to deep pink, and even yellow or nearly orange. It's also late-blooming, typically flowering in early May. In the field, the azalea can be distinguished from R. alabamense and other coastal azaleas by its late spring (early to mid May) flowering time, its wide range of flower color (white, pink or yellow), longer flower buds, its often warty seed capsules with glandular hairs, and its taller stature (3-7 m). Its natural distribution extends from southwestern Alabama to the Chattahoochee Valley in Georgia. [Return to Top]

R. cumberlandense, the Cumberland Azalea, is a low deciduous azalea found in Kentucky, Virginia, Tennessee, North Carolina, Georgia and Alabama. It has long been grown under the name, R. bakeri. It is an excellent, low-growing, late blooming orange to red-flowered azalea suitable for small gardens. The flowers are not large, about 1.5 to 1.75 inches across, and typically range from yellowish-orange to deep red. This species is sometimes difficult to distinguish from the larger flowered R. calendulaceum , but the blossoms generally appear several weeks later after the leaves have fully expanded and the undersides of the leaves are usually waxy white or bluish in color. The species distinction for R. cumberlandense was first described by Lemon and McKay in 1937. This native azalea makes an excellent landscape plant in its own right, but it also hybridizes easily with many of the other species, producing beautiful hybrids in a broad range of colors. R. indicum, or the Satsuki azalea, is one of the oldest evergreen Japanese azaleas, bred since ancient times, and it is the type most commonly used for ornamental pruning. It is a slow-growing evergreen shrub that eventually becomes 3 to 6 feet tall and is hardy to Zone 5, to -15° F. Its 1 1/2-inch-long oval leaves grow on finely twigged branches. In the species, the flowers are red tinged with purple, about 2 to 3 inches wide, but it has been bred in many other colors. [Return to Top]

R. eastmanii, the May white azalea, is a deciduous azalea found in South Carolina in 13 counties of the piedmont and coastal plain to date, officially named, described and proposed as a new species in Novon in September of 1999. It has snowy white flowers with a prominent yellow blotch. Blooming in mid May, the flowers have a distinct, strong, fresh fragrance and measure .8 to 1.5 inches across. Originally thought to be R. alabamense, this plant was first described, noticed and thought to be different from known S.C. species by Charles Eastman in the early 1980s, one hundred years after Dr. C. Mohr discovered R. alabamense. R. eastmanii is low to medium in height, and has a clump habit but does not spread by underground stems. It propagates with relative ease from woody cuttings and makes a delightful landscape plant. [Return to Top]

R. flammeum, the Oconee Azalea (synonymous with R. speciosum ), is a deciduous azalea found in the lower Piedmont from central Georgia to South Carolina. It is seldom cultivated in cooler climates but does well in the southeast. Its blossoms are approximately 1.2 to 1.8 inches across and come is shades of yellowish orange, through orange to deep red. This species can be distinguished from the earlier blooming R. austrinum in that the flowers usually have a blotch, they are not fragrant, nor do they have sticky glandular hairs on the corolla tube. Exact date of discovery for R. flammeum is not known, but plants of this species were first described by Aiton at Kew Gardens in 1789 and were probably sent there by William Bartram prior to that date. This species is a heat tolerant shrub and holds much breeding potential where hot summer stress is a problem. [Return to Top]

R. mucronulatum, the Korean rhododendron, is a deciduous elepidote rhododendron. It is one of the earliest to bloom in Zones 4-8, hardy to -25° F; its pink to purple flowers are susceptible to late frosts. Plant them in a sheltered area to avoid undue exposure. They grow 4 to 6 feet tall. The flowers are only about 1 1/2 inches across, but they appear in very large numbers. 'Cornell Pink' is an especially fine variety, with clear pink flowers unadulterated by the magenta that is present in the blossoms of the original species. R. mucronulatum is not an azalea, but is a rhododendron that resembles an azalea.. Hence, it is often listed in either category. [Return to Top]

R occidentale, the Pacific or Western Azalea, is a tall deciduous azalea found in the Pacific Coast states. The flower color is usually white or pale pink with a strong yellow flare, but my be red, yellow or orange-pink and occasionally the flare is maroon. The foliage turns red and copper shades in the fall. It is among the showiest of all species with bright colors on impressive flowers. However it is difficult to propagate and grow. It is considered impossible to grow on the East Coast. Rhododendron occidentale is the only native azalea that grows naturally west of the Rocky Mountains in the United States. [Return to Top]

R. periclymenoides, formerly R. nudiflorum, the Pinxterbloom Azalea, is a medium deciduous azalea found from Vermont and Massachusetts south to South Carolina and north Georgia and Alabama and west to Tennessee and Ohio. It has showy pinkish-white flowers. Pinxter-flower, with lightly fragrant inch-wide blooms, is perhaps the most common and most familiar wild azalea in the eastern U.S. The name "pinxter" comes not from its coloration but from the Dutch words Pinxter blomachee, which relate to the fact that this is supposedly the azalea that blossoms on Pentecost, 50 days past Easter. We suspect this name was given by folks in northern parts of the plant's range, since in the Carolinas it is more likely to be in bloom for Easter Sunday itself. [Return to Top]

R. prinophyllum, , formerly R. roseum, is a medium deciduous azalea found from southwestern Quebec, through New England, to Appalachian Mountains in Oklahoma and Arkansas at the higher elevations. The flowers are typically rose pink measuring 1.2 to 1.8 inches across and are very fragrant. Assumed to be a form of R. periclymenoides (R. nudiflorum) since its first mention in 1787, it was first described as a distinct species in 1914 by Small but had been under cultivation as A. rosea in Europe before 1812. R. prinophyllum can be distinguished from R. periclymenoides by a number of characteristics including the fact that it is usually deeper pink in color and with a strong cinnamon to clove fragrance. R. prinophyllum is a good landscape plant for northeastern gardens, but may be more difficult in the south because of summer heat. [Return to Top]

R prunifolium, the Plum Leaf Azalea, is a medium deciduous azalea found on the Georgia-Alabama border. The color ranges from orange-red to red, and occasionally orange or yellow. This species blooms very late, usually in late June or in July. First collected by R.M. Harper in 1913, R. prunifolium prefers more shade than most deciduous azaleas to prolong the flowers during hot summer months. [Return to Top]

R. schlippenbachii, the royal azalea, is a deciduous Korean species. It has soft green leaves that grow in whorls around the stem and turn yellow, orange and crimson in the fall. It is so lovely that man can hardly hope to improve upon its soft pink flowers. They are 3 inches across, and freckled on the upper petals and have a delicate fragrance. Schlippenbachii tolerates less acid soils in Zones 5-8 than the other species. It is hardy to -10° F and grows to 6 to 10 feet tall. [Return to Top]

Delicate R. vaseyi, pinkshell azalea, grow best in the moist soil bordering ponds in Zones 5-8, hardy to -10° F, where they grow 6 to 8 feet tall and bears 1 1/2-inch pink flowers in late spring to early summer. Its leaves turn red in autumn. [Return to Top]

Low, wet areas in Zones 3-8 suit the late-blooming R. viscosum, swamp azalea, which bears extraordinarily fragrant 1 1/2- to 2-inch white blossoms tinged with pink in midsummer on branches up to 9 feet tall. It is hardy to -20° F. The leaves turn orange or bronze red in the fall. [Return to Top]

R. yedoense, the Yodogawa azalea, has 2-inch double reddish purple flowers in late spring. Plants rarely grow more than 3 feet tall, but may spread to 6 feet in diameter. It is hardy in Zone 6 to -5° F. The variety R. yedoense 'Poukhanense', Korean Yodogawa azalea, has single flowers and is a bit more resistant to winter cold than the double-flowered type. The leaves of both drop in Northern gardens, but remain nearly evergreen in milder climates. [Return to Top]

How To Grow Deciduous Azaleas

All of the deciduous azaleas are alike in their need for moist well-drained, acid soil (pH 4.5 to 5.5) that has been well supplemented with peat moss or leaf mold. Azaleas will grow in full sun or light shade, but light shade is preferable in hot areas. Pruning is almost never required.

Deciduous rhododendrons are propagated by seed, grafting or cutting. Deciduous azaleas are very tricky to propagate from cuttings. Tissue culture is used to propagate varieties that are difficult to root. It is a laboratory technique that is very successful.

Take cuttings of deciduous azaleas when the new growth is soft and pliant. This is often coincident with time of bloom in early June. The ability to root decreases rapidly as new growth matures. Select cuttings daily for best results. Trim cuttings below a node (overall length of cuttings 3 to 5 inches) and dip in a root hormone containing fungicide. Insert in a medium of 60% peat moss and 40% horticultural perlite. Usually bottom warmth of 75°F is used to encourage root growth. In late August, transplant cuttings that are rooted and grow on in the greenhouse with supplementary light (14-hours a day) to prevent dormancy and induce new growth. In the fall after new growth has matured, transfer to a cool, frost-free cool (35°F to 41°F) environment to induce dormancy. As new growth develops in the spring, transfer plants to a shaded environment. [after "Rhododendrons and Azaleas" by J. Lounsbery, Horticultural Research Institute of Ontario, Canada]

Where soils are moist and naturally very acid, deciduous azaleas and rhododendrons thrive in partial shade, especially in hot areas, but grow reasonably well in full sun. The species and hybrids listed need very little pruning and seldom have serious infestations. Their foliage may turn to bright hues in autumn.