Deciduous Azaleas
Azaleas, including deciduous azaleas, are members of the rhododendron genus. The basic difference between azaleas and other rhododendrons 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.
6 deciduous azalea species are in the Sciadorhodion Section of the Azaleastrum subgenus of Rhododendron and are native to North America, Japan, Korea, and adjacent areas of Russia. 18 deciduous azalea species are in the Pentanthera Section of the Hymenanthes subgenus of Rhododendron and are mostly native to North America, but with R. luteum in Asia Minor and R. molle in China & Japan.
Most deciduous azalea used in landscaping are hybrids of two, but usually more, Rhododendron species. Many of the species used in hybridization are azaleas native to eastern North American with additional azalea species from Japan or Europe. When buying deciduous azaleas always look for those specifically mentioning mildew resistance. The native American azaleas are among the most powdery mildew resistant, especially R. arborescens, R. canadense, R. canescens, and R. vaseyi. Among hybrid deciduous azaleas, ‘Millennium’, ‘Parade’, ‘Tri-Lights’, ‘Lemon Lights’, ‘Fragrant Star’, ‘Mandarin Lights’, ‘Northern Hi-Lights’, and ‘Snowbird’ show good powdery mildew resistance.
Successful hybridization of deciduous azaleas was initiated in the 1820's by a Belgian baker living in Ghent. He started by crossing R. calundulaceum with R. prinophyllum. 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. Meanwhile, in Japan many hybrids of R. japonicum were found. These were called the Mollis Azaleas. Some are selected forms of R. japonicum and others are hybrids. These were actively hybridized in Holland in the 1860's. In the 1870's, the Knapp Hill Azaleas were developed by Anthony Waterer from Ghent Azaleas and R. sinensis from China. In 1922, Lionel de Rothschild of Exbury, Southampton, UK, obtained many seedlings of Mollis Azaleas and bred what became known as the Exbury Azaleas.
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Examples of Deciduous Azalea Species
R. alabamense, the Alabama Azalea – 4', -5F. It is a deciduous azalea found in Alabama and adjacent states. It has snowy white flowers with a prominent yellow blotch. Blooming in midseason, the flowers have a distinct lemon-spice fragrance and measure .8 to 1.5 inches across. Originally thought to be a white form of R. periclymenoides (R. nudiflorum), this plant was first described by Dr. C. Mohr in 1883. It grows naturally in north central Alabama, and western to central Georgia and South Carolina. R. alabamense is low to medium in height, and spreads by underground stems or stolons. It propagates with relative ease from soft wood cuttings and makes a delightful landscape plant.
R. albiflorum – 3', -25F. It is an upright, white-flowering, deciduous azalea that is found in western North America from British Columbia and Alberta to Oregon and Colorado near the timberline. It does not do well in cultivation except in Scotland.
R. arborescens, the sweet or smooth azalea – 5', -15F. It 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. It is a deciduous azalea found from Pennsylvania south to Georgia and Alabama. It is a good late flowering, scented species that can be used in cultivation. It has white to blush pink flowers with red stamens, and a very strong fragrance similar to heliotrope. It blooms in late spring to early summer and individual flowers measure 1.5 to 2 inches across. First described by John Bartram in 1814, this species has a wide distribution in the eastern United States, but can usually be found growing near streams or moist areas. It is sometimes known as the "Smooth Azalea" because the stems are very smooth and do not have hairs similar to the other azaleas. An excellent landscape plant, R. arborescens can perfume a wide area when in bloom. Relatively easy to propagate, there are a number of excellent forms in the trade. It is resistant to powdery mildew.
R. atlanticum, the Atlantic Azalea or Coastal Azalea – 3', -15F. It 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 southeastern 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 that will restrict the spreading habit. [Return to Deciduous Azalea Species Index]
More Deciduous Azalea Species
R. austrinum, the Florida Azalea – 5', -5F. It is a deciduous azalea found from northwest Florida to Georgia, Alabama and southeast Mississippi. This plant blooms in early spring as the leaves are beginning to expand. The fragrant blossoms come in shades of orange through gold and yellow, and measure approximately 1 to 1.5 inches across. This species has very long stamens and the tube of the flower is often flushed with red but there is no blotch. Discovered by Dr. A. W. Chapman before 1865, R. austrinum is similar in many respects to R. canescens including the sticky glandular hairs on the flower tube, but differs in the color variations which are orange to yellow rather than pink to white. R. austrinum makes an excellent landscape plant as well as a valuable hybridizing resource, especially in southern gardens where heat tolerance is important.
R. calendulaceum, the flame azalea – 6', -10F. It 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.
R. canadense, the Rhodora Azalea – 2', -25F. It 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. It is resistant to powdery mildew.
R. canescens, the Florida Pinxter or Piedmont Azalea – 5', -5F. It 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. periclymenoides are 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. It is resistant to powdery mildew. [Return to Deciduous Azalea Species Index]
More Deciduous Azalea Species
R. colemanii, the Red Hills azalea – 6', -5F. 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.
R. cumberlandense, the Cumberland Azalea – 4', -15F. It 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. Lemon and McKay first described the species distinction for R. cumberlandense 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. eastmanii, the May white azalea – 3', -15F. It 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.
R. flammeum, the Oconee Azalea (synonymous with R. speciosum) – 3', -5F. It 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 in 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 Deciduous Azalea Species Index]
More Deciduous Azalea Species
R. luteum, the Honeysuckle Azalea – 4', -10F. It is a species of Rhododendron native to southeastern Europe and southwest Asia. In Europe, it occurs from southern Poland and Austria south through the Balkans and east to southern Russia, and in Asia, east to the Caucasus. Despite the sweet perfume of the flowers, the nectar is toxic, containing grayanotoxin; records of poisoning of people eating the honey date back to the 4th century BC in Classical Greece. [Return to Deciduous Azalea Species Index]
R molle ssp. japonicum, the Japanese Azalea – 4', -15F. It is an upright, bushy shrub that is cold hardy down to -10 degrees F with small, oblong leaves turning red in autumn. The orange-red flowers are borne in large, showy trusses in mid-spring just before the leaves emerge and carry a sweet fragrance. In the 1800's many form of R. molle ssp. japonicum were found. These were called the Mollis Azaleas. Some were selected forms of R. molle ssp. japonicum and others were hybrids.
R occidentale, the Pacific or Western Azalea – 5', -5F. It 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 may 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.
R. periclymenoides, formerly R. nudiflorum, the Pinxterbloom Azalea – 5', -15F. It 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.
R. prinophyllum, formerly R. roseum – 5', -25F. It 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 Deciduous Azalea Species Index]
More Deciduous Azalea Species
R prunifolium, the Plum Leaf Azalea – 4', -10F. It 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.
R. schlippenbachii, the royal azalea – 4', -20F. It 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. Schlippenbachii tolerates less acid soils in Zones 5-8 than the other species. Unlike most other deciduous azaleas, it needs some shade to thrive. It is hardy to -10° F and grows to 6 to 10 feet tall.
R. vaseyi, pinkshell azalea – 4', -15F. It grows best in the moist soil bordering ponds in Zones 5-8, hardy to -10° F, where it grows 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. It is resistant to powdery mildew.
R. viscosum, swamp azalea – 6', -20F. Low, wet areas in Zones 3-8 suit this late-blooming plant 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 Deciduous Azalea Species Index]
Examples of Hybrid Deciduous Azaleas
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Ghent Azaleas from Belgium
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.
The Ghents are the oldest of the hybrid deciduous azaleas. They are the result of crossing species of eastern North America with their one European relative, in this case the Pontic azalea, R. luteum, and therefore owe nothing to the Himalaya nor to Eastern Asia. Which American species were used is not known, but R. calendulaceum, R. periclymenoides, and R. viscosum were certainly among them. Some may be purely American in parentage, especially the later flowering sorts. It is probable that most of the present commercial stock derives from the crosses made by the Belgian baker P. Mortier of Ghent in the 1820s and 1830s, which soon entered the trade and had reached Britain by 1831. In his 1836 catalogue, Loddiges of Hackney listed seventy-two ‘Hybridae Belgicae’, among them two still cultivated today – ‘Gloria Mundi’ and the well-known ‘Coccinea Speciosa’. Ghent-type crosses were also made at Highclere by Gowen for the Earl of Carnarvon, and of these Loddiges offered twenty-four, but none of the names appears in any modern list.
An interesting character of the Ghent azaleas (and of later hybrids deriving from them) is that seedlings occasionally occur in which the stamens are converted into petals. Since the stamens are always five in number and alternate with the corolla-lobes, the result is a fairly symmetrical ‘hose-in-hose’ flower. The best known of these double Ghents is ‘Narcissiflora’. There is another group with double flowers of similar form known as Rustica Flore Pleno. These were put into commerce by Charles Vuylsteke of Loochristi, near Ghent, in 1888, and are usually supposed to be the result of crossing double Ghents with Mollis azaleas. Like the Mollis azaleas they were intended primarily for forcing, and had the advantage that their flowers lasted longer. The best known of this group is ‘Norma’.
- Baltic Amber – 5', -10F. It has yellow flowers, the leaves have silvery markings.
- Corneille – 6', -15F. It has soft double pink flowers.
- Daviesi – 4', -15F. It has white flower with yellow centers.
- Irene Koster – 6', -16F. It is late blooming pale rose pink flowers with a gold flare. Fragrant.
- Magic – 5', -10F. It has yellow flowers change to orange as they mature.
- Nancy Waterer – 5', -10F. It has large, golden-yellow flowers.
- Narcissiflora – 6', -15F. It has double light yellow flowers with pointed petals. [Return to Hybrid Deciduous Azalea Index]
Mollis Azaleas
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 Mollis azaleas, as they are usually called, derive mainly from R. japonicum, the only Japanese member of the Luteum subseries, which in the last century was generally known as Azalea mollis, but its Chinese relative, then known as Azalea sinensis, enters into the parentage of some varieties, The name Azalea mollis was wrongly used, for it belonged properly to the Chinese azalea, which therefore takes the name R. molle (Bl.) Wils., while the Japanese species (the Azalea mollis of 19th-century gardens) becomes R. japonicum.
The Mollis group owes its origin to the great Belgian nurseryman Louis van Houtte, who had named some twenty varieties by 1873. Van Houtte stated that his new azaleas were the result of thirty years of breeding, which means that their origin goes back to the early 1840s. R. japonicum commonly bears orange-red or flame-red flowers in the wild, rarely yellow. The van Houtte varieties ranged in color from lemon- and buff-yellow through rose and salmon to orange and salmon-red. Furthermore, the beautiful ‘Chevalier de Reali’ has very fragrant flowers, whereas those of R. japonicum are almost scentless. It is also of possible significance that van Houtte had an azalea, called by him Azalea sinensis alba, which, as Rehder suggested, seems to be a hybrid between R. molle and R. viscosum. The pale yellow varieties put out by van Houtte may well have derived from this, and possibly some of the others.
By the late 1870s the Mollis azaleas had become important commercial plants but, like most of the azaleas grown in the last century, they were looked on primarily as subjects for the decoration of house or conservatory. The group was soon taken up and further developed by the Dutch nurserymen, and it was also a Dutch firm – M. Koster and Sons – who first put into commerce varieties that are known to have been the result of crossing R. japonicum with R. molle. The Koster varieties, which were actually raised by another Dutch grower, were first put into commerce in 1892, and many others followed before the end of the century.
In the course of their breeding, M. Koster and Sons discovered that if certain selected Mollis azaleas are crossed, the progeny is more or less uniform in color, and it is therefore possible, by repeating the cross annually, to produce quantities of seedling azaleas true to color. The first Mollis azalea to be propagated in this way was ‘Koster’s Brilliant Red’, which was therefore not originally a clone. But some of the seedlings have since been propagated vegetatively, so that the name now covers several similar but not identical clones. Other Dutch nurseries now produce such line-hybrids, but the seedlings are usually sold to color, without a distinguishing cultivar name.
- Anthony Koster – 5', -10F. It has bright yellow flowers with a vivid orange blotch.
- Arneson Flame – 5', -10F. It has red flowers on upright disease resistant plant. A heavy bloomer.
- Arneson Gem – 3', -15F. It golden flowers are edges in orange. It is a prolific bloomer on a compact plant.
- Christopher Wren – 5', -10F. It bright yellow flowers flushed with red, buds orange red. [Return to Hybrid Deciduous Azalea Index]
Knap Hill Azaleas
Knap Hill Hybrids (Exbury, Knap Hill, Ilam and Slocock Hybrid azaleas) are exceptional hybrids developed at the English Knap Hill nursery of Anthony Waterer, 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. In New Zealand, Edgard Stead of Ilam, near Christchurch, developed the Ilam Hybrids. 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.
The Knap Hill azaleas, as usually defined, are a miscillaneous collection of hybrids that are derived from both the Pontic-American and the east Asiatic species and also have another character in common, namely that they all have in their ancestry azaleas bred in the Knap Hill Nursery in the time of the two Anthony Waterers, father and son, who are therefore the founders of the group, though few of the clones now in commerce were actually raised by them.
The history of the Knap Hill group goes back to the middle of the nineteenth century, when Anthony Waterer and his partner set out to improve the Ghents by crossing them with the Chinese azalea R. molle, formerly known as Azalea sinensis. In 1861 the Gardeners’ Chronicle reported: ‘Some fine seedlings have been obtained, with blooms of large size and possessing great richness and variety of color. They also have the good property of being late bloomers. Though among them orange and flame-colored tints prevail, yet one we remarked had a crimson top petal and the rest rose; equally remarkable combinations of color were also to be met with in other sorts’ (Gard. Chron. (1861), p. 531).
The Exbury strain of the Knap Hill azaleas demands special mention, since it has developed to the stage where it is surely entitled to independent rank. About 1921 Lionel de Rothschild acquired from Anthony Waterer an azalea named ‘George Reynolds’ which had butter-yellow flowers of very large size. Curiously enough, it is very uncharacteristic of the Knap Hill breed, being nearer to a Mollis-Sinensis hybrid than to a Ghent, which may explain why Anthony Waterer was willing to part with it. This was crossed at Exbury with some unnamed Knap Hill azaleas with orange flowers, and one of the seedlings from this cross received an Award of Merit in 1934 under the name ‘Hotspur’. A few years after Anthony Waterer’s death, Lionel de Rothschild acquired a financial interest in the Knap Hill Nursery and was therefore in a position to draw on its resources. He also used true R. molle, raised from seeds collected in China by Forrest and by Rock. Discarding all but the best seedlings, and crossing only within the various color-groups, he produced a splendid strain that owes as much to his efficiency and sound judgment as it does to the work of the Anthony Waterers. It is doubtful whether any Boskoop nurseryman, breeding for a competitive market, could have achieved as much as this amateur did in such a short space of time. Many Exbury clones have been named and received awards, but the greater part of those in cultivation are seedlings supplied to color, of which large quantities have been exported to the United States.
The Knap Hill group of azaleas are mostly of moderate growth, to about 5 ft. The young foliage in many clones and seedlings is bronze-tinted, and many also give excellent autumn color. The flowers are more or less fragrant, larger than in the Ghents, sometimes much larger, and the tube of the corolla is generally longer than it is in the Mollis type of azalea. The influence of R. molle is often shown by a flare of discrete markings, while others have the solid flare characteristic of the Ghents. The group as a whole, including the Exbury strain, is a very large one and is open-ended, for new sorts are being named all the time.
- Cecile' (Exbury) – 6', -15F. It has red flowers with an orange-yellow blotch.
- Fireball' (Knap Hill) – 5', -20F. It has brilliant red flowers on an upright plant.
- Frills' (Knap Hill) – 4', -10F. It's orange, semidouble, frilly flowers fade to a yellow-orange in the center.
- Gibraltar (Exbury) – 5', -15F. It is brilliant orange, flushed with red, ball cluster, on a compact plant.
- Homebush (Knap Hill) – 6', 0F. It has semi-double rose pink flowers in a tight ball shaped truss.
- King Red (Exbury) – 5', -15F. It has vivid red, slightly ruffled, large ball cluster, compact plant.
- Klondyke (Exbury) – 8', -15F. It has golden-yellow flowers. Striking bronze new foliage.
- Yellow Giant' (Ilam) – 4', -10F. Its flowers are brilliant yellow with a darker flare, about 8 cm across. [Return to Hybrid Deciduous Azalea Index]
Occidentale Hybrids
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Washington State
Centennial |
The Occidentale hybrids consist mainly of a group of rather similar clones raised by M. Koster and Sons of Holland by crossing R. occidentale with Mollis-Sinensis azaleas in 1895. All are lovely, with delicately colored fragrant flowers, borne in late May or early June, and growing to 5 or 6 ft. high, but are best kept away from more brightly colored azaleas.
R. occidentale is closely related to the East American members of the Luteum subseries, having the white flowers of R. viscosum but in other respects being near to R. calendulaceum. But being a native of western North America it was introduced later – around 1851 by William Lobb for Messrs Veitch. This was apparently a poor form (the species is very variable). However, the elder Anthony Waterer, probably through his American friends, introduced a finer form in the 1870s, for which he received a Botanical Certificate in 1886. Being very late-flowering it had potentialities as a parent and was crossed at Knap Hill with Ghent azaleas, presumably of the improved type then being bred there. By 1890, there were numerous seedlings of this new race in the nursery, with flowers ranging from white through cream to pink and deep pink, fragrant, with unusually long tubes. They flowered very late – some at the end of June and in early July. They include:
- Bridesmaid – White with a yellow flare; buds pale greenish yellow. Leaves bright green. Dense habit.
- Delicatissima – Soft yellow in the bud, opening cream with a slight tinge of pink, about 21⁄4 in. wide; flare yellow, not conspicuous. Fragrant.
- Irene Koster – Beautiful, later blooming, light rose-pink flowers have a showy yellow-gold flare on the upper petals. The buds are especially attractive with stripes of pink that run their length, providing contrast to the open flowers. Growth habit is a little broader and less tall than many deciduous azaleas. Very fragrant.
- Washington State Centennial – A relatively new Occidentale hybrid from Dr. Frank Mossman for Washington State's 1989 centennial. The flowers open a light orange-yellow, gradually softening to white with a blotch of vivid glowing yellow on the upper petal. The frilled petals and fragrant flowers fill the garden with charm and sweetness each spring. The leaves are very shiny and resistant to powdery mildew. Very fragrant. [Return to Hybrid Deciduous Azalea Index]
Maid in the Shade® Azaleas from Transplant Nursery in Lavonia, GA, by Jeff Beasley
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:
- Summer Lyric - Flowers are a mix of pink with yellow throats.
- Lisa's Gold - R. austrinum cultivar. Golden-yellow flowers in early spring. Zone 6. Fragrant. Upright.
- Camilla's Blush -R. canescens cultivar. Blushing pink blooms that hummingbirds find irresistible. Zone 6. Fragrant. Upright.
- Kelsey's Flame - Bright yellow and orange flowers. Zone 6. Fragrant. Upright.
- Lavender Girl - R. periclymenoides cultivar. Pale lavender flowers
- My Mary - Hybrid. Pale yellow flowers, named as a tribute from George Beasley to his wife Mary. Zone 6. Fragrant. Upright.
- Rosy Cheeks - Dark rose flowers with golden throats. Its fragrance can rival that of a rose.
- Nacoochee Princess - Regal white flowers that are tinged with pink. [Return to Hybrid Deciduous Azalea Index]
Northern Lights by H. Pellet at the University of Minnesota
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Rosy Lights,
Northern Lights |
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Spicy Lights,
Northern Lights |
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Northern Hi-Lights,
Northern Lights |
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Tri-Lights,
Northern Lights |
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:
- Pink Lights Azalea – 3', -35F. Introduced in 1984. The flower has a light pink color with a sweet floral scent. Mature plants will have a height and spread of about eight feet. The plant is extremely floriferous.
- Rosy Lights Azalea. – 4', -35F. Introduced in 1984. The flower color is a deep rosy pink and plants are extremely floriferous. Plant height and spread is about eight feet.
- White Lights Azalea. – 5', -35F. White Lights is a hybrid of Rhododendron prinophyllum and a white flowered Exbury hybrid. The flower buds have a delicate pale pink cast but open to a white flower with a slight yellow blotch. This cultivar is extremely floriferous and has a flower bud hardiness rating of -35 degrees F. Plant height and spread is about five feet.
- Spicy Lights Azalea. – 3', -35F. Spicy Lights is a selection from hybrids having Rhododendron prinophyllum in their background. The flower has a salmon color with a slight fragrance. Flower bud hardiness is rated at -35 degrees F. Plant height is about six feet and spread is about eight feet.
- Orchid Lights Azalea. – 2', -35F. Introduced in 1986, Orchid Lights Azalea is a hybrid of Rhododendron canadense and Rhododendron x kosteranum. The orchid-colored flowers are 1-1/2 inches across and are sterile, so seed capsules are not produced. Flower bud hardiness is rated at -45 degrees F. The compact plants of Orchid Lights will mature at an average height of three feet and a spread of three to four feet.
- Golden Lights Azalea. – 5', -30F. Introduced in 1986, Golden Lights Azalea is a hybrid of an Exbury seedling and an unidentified azalea seedling. The golden flowers are 1-1/2 to 2 inches across and have a cold hardiness rating of -30 degrees F. The mature plants reach an average height and spread of four feet. Golden Lights has the added advantage of greater resistance to powdery mildew than some other hybrid azalea cultivars.
- Northern Hi-Lights Azalea. – 3', -25F. Introduced in 1994, Northern Hi-Lights Azalea is a hybrid of an Exbury seedling and an unidentified azalea seedling. It is a hybrid with the same parents as "Golden Lights". The flowers are creamy white with a bright yellow upper petal and have a cold hardiness rating of -30 degrees F. Plants grow relatively slowly to four feet high and four to five feet wide. The dark green foliage has some resistance to powdery mildew.
- Mandarin Lights Azalea. It is resistant to powdery mildew.
- Lemon Lights Azalea. It is resistant to powdery mildew.
- Tri-Lights Azalea. It is resistant to powdery mildew.[Return to Hybrid Deciduous Azalea Index]
Aromi Azaleas by Dr. Gene Aromi of Mobile, AL
The Aromi hybrids were developed by Dr. Gene Aromi, a retired University of Southern Alabama professor, and his wife Jane in Mobile, Alabama. In 1971 they began hybridizing Exbury azaleas with southern native species to create heat tolerant, large flowered, fragrant deciduous azaleas. Over 100 of these deciduous hybrids are named, and 8 of them are registered.
- Aromi Sunny-side-up. R. austrinum x 'Golden Sunset.' Pale yellow buds open to lemon yellow flowers , darker blotch.
- Aromi Sunrise. 'Hiawatha' x R. austrinum. Red orange buds open to yellow orange flowers with darker shading in the center.
- Aromi Sunstruck. R. austrinum x 'White Swan.' Pale yellow buds open to lemon yellow flowers, deep yellow blotch.
- Frontier Gold. 'Rothschild Orange' x R. austrinum. Orange-scarlet buds open to golden flowers with scarlet shading, deeper golden blotch.
- High Tide. Ivory with gold blotch and light pink flush petals. It has good heat tolerance.
- Liz Colbert. R. serrulatum x R. austrinum. Brick red buds open to light peach flowers, yellow orange blotch.
- Pathfinder. 'Rothschild Orange' x R. austrinum. Orange buds open to golden flowers , deep golden blotch.
- Pink Carousel. R. austrinum x 'Red Letter.' Scarlet buds open to pale pink flowers, strong golden blotch.
- Red Pepper 'Gallipoli' x R. austrinum. Red-orange flowers, deeper blotch. [Return to Hybrid Deciduous Azalea Index]
Weston Azaleas by Mezitt, Hopkinton, MA
The Weston hybrids were developed at Weston Nurseries in Hopkinton, MA, by Edwin Mezitt and his son, R. Wayne Mezitt. They form a family of summer-flowering deciduous azaleas. They are bred for superior foliage, especially fall foliate, and powdery mildew resistance.
- Lollipop - 4', -20F. This lovely azalea has a distinctive fragrant pink bloom with a daring yellow flare that turns an attractive silvery pink as it ages.
- Millennium - 4', -5F. The dusty-red flowers set against blue green foliage blend in the landscape. It's very late flowering and powdery mildew resistant. Fragrant.
- Parade - (R. cumberlandense x R. viscosum) 6', -25F. Deep pink, 1.5" trumpet blooms on this robust plant open in July, emitting a soft, sweet fragrance. Very hardy and very tall. It can reach heights of up to 8'. It is powdery mildew resistant
- Pink and Sweet - 4', -20F. A very hardy, semidouble selection that has fragrant, purple-pink flowers with a golden flare in the throat. It blooms in June-July.
- Weston's Innocence - 3', -25F. A spectacular hybrid that blooms in mid to late June. The strongly fragrant white flowers are abundant. A vigorously growing wide plant with upright branches, it is compact and becomes mound shaped with age. The glossy leaves are resistant to powdery mildew and have a deep red fall color. Takes full sun.
- Weston's Lemon Drop - 3', -35F. Syn. 'Lemon Drop'. A summer flowering deciduous Azalea. Soft pink buds open to fragrant, yellow blossoms in July. Glossy green leaves turn a dark, wine-red color in fall. Grows 4' x 4' wide. [Return to Hybrid Deciduous Azalea Index]
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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.
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Directory of Contents for Henning's Rhododendron & Azalea Pages
•• Providing Information about the Genus Rhododendron since 1996
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Articles Published by the American Rhododendron Society
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Last Updated:
July 6, 2020
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