Despite a degree of paraphyly, the subgenus Rhododendron was otherwise untouched with regard to its three sections but four other subgenera were eliminated and one new subgenus created, leaving a total of five subgenera in all, from eight in Chamberlain's scheme. Other significant areas of diversity are in the mountains of Korea, Japan and Taiwan. [68] Other examples include the PJM hybrids, formed from a cross between Rhododendron carolinianum and R. dauricum, and named after Peter J. Mezitt of Weston Nurseries, Massachusetts. [25] It was not until 1893 that Koehne appreciated the significance of scaling and hence the separation of lepidote and elepidote species. Most rhododendron flowers are bell-shaped and have 10 stamens. [29][30] Most of the Balfourian series are represented by Sleumer as subsections, though some appear as sections or even subgenera. There are over 28,000 cultivars of Rhododendron in the International Rhododendron Registry held by the Royal Horticultural Society. Revisions by Goetsch et al. Evergreen rhododendrons - large group of evergreen shrubs that vary greatly in size. It is admired for its distinctive flavor and color.[81]. Rhododendrons are hardy evergreen plants that will flower from late winter through to early spring. Larger commercial growers often ship long distances; in the United States, most of them are on the west coast (Oregon, Washington state and California). How to Plant Rhododendron & Azaleas. Yes, it does! giganteum, reported to 30 m (100 ft) tall. If you are new to growing Rhododendrons, this should be your first choice, since it is hardy in part-sun or shade, cold-tolerant and undemanding – a real beauty for easy growing and trouble-free gardening. They do like sun, but not full or bright sun. They can be planted among other shrubs of similar size or by themselves in a grouping. [51], Rhododendrons are grown commercially in many areas for sale, and are occasionally collected in the wild, a practice now rare in most areas. Extensive information on rhododendron species: the history of their discovery, botanical details, toxicity, classification, cultural conditions, care for common problems, and suggestions for companion plants by Steve Henning. Then look no further than the hardy rhododendron. Quick facts. The first two subgenera (Rhododendron and Hymenanthes) represent the species commonly considered as 'Rhododendrons'. They can get real big. Plant in spring or early fall. The industry is promoted by the state government with tax benefits, looking to promote this industry as a full-fledged subclass of its economy. Terminology from the Sleumer (1949) system is frequently found in older literature, with five subgenera and is as follows; In the later traditional classification, attributed to Chamberlain (1996), and as used by horticulturalists and the American Rhododendron Society,[44] Rhododendron has eight subgenera based on morphology, namely the presence of scales (lepidote), deciduousness of leaves, and the floral and vegetative branching patterns, after Sleumer (1980). [52], In the Indian state of Himachal Pradesh, rhododendron flowers have been used for some time to make popular fruit and flower wines. Rhododendrons are stunning bushes that produce big, beautiful blossoms in the spring (and in the case of some varieties again in the fall). A good resource for rhododendron cultivars is Virginia Tech's American Rhododendron Plant Society Registry. Rhododendrons range in size from dwarf shrubs to medium-sized trees. These giants include varieties like Caractacus (Rhododendron Caractacus), hardy down to USDA zone 4 and bearing rosy red blooms, according to the American Rhododendron Society, or the purple-flowered Whidbey Island (Rhododendron 'Whidbey Island') hardy down to USDA zone 6. In addition to the two separate genera included under Rhododendron by Chamberlain (Ledum, Tsusiophyllum), Goetsch et al.. added Menziesia (Clade C). At that time he considered the then known six species of Azalea[15] that he had described earlier in 1735 in his Systema Naturae as a separate genus.[16][17]. Cullen of the Edinburgh group, placing more emphasis on the lepidote characteristics of the leaves, united all of the lepidote species into subgenus Rhododendron, including four of Sleumer's subgenera (Rhododendron, Pseudoazalea, Pseudorhodorastrum, Rhodorastrum). They like well drained acid soil. Both tropical and cool climate types are available, the tropical types will tolerate cold winters and hot summers, the cool climate varieties do not grow well in the hot tropical areas. Pink Rhododendron (Rhododendron campanulatum) is the State Flower of Himachal Pradesh, India. Some are in big heads, large bells, some have elongated bells. [48] It is an introduced species, spreading in woodland areas and replacing the natural understory. Mother of Pearl (Rhododendron 'Mother of Pearl') and Mount Everest (Rhododendron 'Mount Everest') both bear white flowers and are hardy down to USDA zone 6. Discover rhododendrons. The remaining small subgenus Therorhodion with its two species was left intact. For a comparison of the Sleumer and Chamberlain systems, see Goetsch et al. They can also go the other direction and be grown as small, manageable plants in containers. Information on rhododendrons at the Ericaceae web pages of Dr. Kron at Wake Forest University. [30][31] In 1986 Philipson & Philipson raised two sections of subgenus Aleastrum (Mumeazalea, Candidastrum) to subgenera, while reducing genus Therorhodion to a subgenus of Rhododendron. They like moist, rather cool air. [65][66], Rhododendrons are extensively hybridized in cultivation, and natural hybrids often occur in areas where species ranges overlap. [36] Then Judd & Kron moved two species (Rhododendron schlippenbachii, R. quinquefolium) from section Brachybachii, subgenus Tsutsusi and two from section Rhodora, subgenus Pentanthera (R. albrechtii, R. pentaphyllum) into section Sciadorhodion, subgenus Pentanthera. The single species of monotypic subgenus Candidastrum (Rhododendron albiflorum) was moved to subgenus Azaleastrum, section Sciadorhodion. Difference Between Mountain Laurel & Rhododendrons, American Rhododendron Plant Society Registry, American Rhododendron Society Massachusetts Chapter, Missouri Botanical Garden: Rhododendron (PJM Group), Virginia Tech: Journal American Rhododendron Society. Some hybrids have fragrant flowers[67]—such as the Loderi hybrids, created by crossing Rhododendron fortunei and R. Rhododendrons get to be 4 to 6 feet, it takes about 6 years to reach full height. For instance Rhodora (Linnaeus 1763) for Rhododendron canadense, Vireya (Blume 1826)[18] and Hymenanthes (Blume 1826) for Rhododendron metternichii, now R. degronianum. I was asked recently to do what I could to save a roughly 20-year-old Rhododendron, which had grown to about 5 feet. They may be either evergreen or deciduous. In some species, the undersides of the leaves are covered with scales (lepidote) or hairs (indumentum). The discontinued subgenera are Pentanthera, Tsutsusi, Candidastrum and Mumeazalea, while a new subgenus was created by elevating subgenus Azaleastrum section Choniastrum to subgenus rank. ’Scarlet Wonder’ is a red-flowered dwarf variety with a maximum height and spread of just 2 to 3 feet, perfect for small spaces. They can be planted by themselves but are also attractive when planted in groups. A small number, however, possess excellent cold hardiness and grow well in Iowa. Similarly the single species in monotypic subgenus Mumeazalea (Rhododendron semibarbatum) was placed in the new section Tsutsusi, subgenus Azaleastrum. Most amateur gardeners do not grow rhododendrons from seed, as they take between 2-10 years to flower. Most rhododendrons thrive in humid climates with mild winters, although there are hardy varieties that survive colder temperatures. They are one of the most under rated rhododendron plants available for sale. griffithianum. 3 to 6 Feet Tall The majority of rhododendrons fall between about 3 to 6 feet in height. Chief amongst these were Maximovicz's Rhododendreae Asiae Orientali[23] and Planchon. Growing them is easy, here's how. Shown here is the traditional classification, with species number after Chamberlain (1996), but this scheme is undergoing constant revision. [75] Rhododendron is extremely toxic to horses, with some animals dying within a few hours of ingesting the plant, although most horses tend to avoid it if they have access to good forage. Potted rhododendrons need heath to grow … Of the first two of these, the species are predominantly found in the area of the Himalayas and Southwest China (Sino-Himalayan Region). Get involved. Space plants 2 to 6 feet apart, depending on their estimated mature size. [50]:540–541 They can self-propagate by sending up shoots from the roots. © Copyright 2020 Hearst Communications, Inc. Rhododendron arboreum is also the state tree of the state of Uttarakhand, India. Rhododendron is also the provincial flower of Jiangxi, China and the state flower of Nagaland, the 16th state of the Indian Union. In areas with poorly drained or alkaline soils, rhododendrons are often grown in raised beds using media such as composted pine bark. The small polyphyletic subgenera Pentanthera and Azaleastrum were divided between two clades. The rootstock is able to grow in calcium-rich soil up to a pH of 7.5. Rhododendrons that stand 1 to 3 feet tall are often considered dwarfs. Growing rhododendron successfully requires the proper planting spot for the rhododendron bush. 1 to 3 Feet Tall. Of the three minor subgenera, all in C, two were discontinued. If the growing position is very sunny the smaller compact and deciduous varieties will do best. R. ponticum is difficult to eradicate, as its roots can make new shoots. Everything you need to know about choosing the right rhododendron for you. The shade-tolerant rosebay (Rhododendron maximum) grows wild from Nova Scotia to Georgia. How to grow rhododendrons. [37] Finally Chamberlain brought the various systems together in 1996, with 1,025 species divided into eight subgenera. How to Grow Dwarf Rhododendrons. Species in this genus may be part of the heath complex in oak-heath forests in eastern North America. Many of our competitors only offer smaller sizes, which will take years to reach an appealing height. They will rot in standing water. giganteum, reported to 30 m (100 ft) tall. [citation needed], In the language of flowers, the Rhododendron symbolizes danger and to beware.[77]. [2][11][17][38][39], The era of molecular analysis rather than descriptive features can be dated to the work of Kurashige (1988) and Kron (1997) who used matK sequencing. Rhododendrons are closely related to Azaleas. They thrive in a moist, well-drained, humus-filled soil with a pH of 5.0 to 6.0, enriched with peat moss or leaf mold. Discover rhododendrons. They confirmed that the genus Rhododendron was monophyletic, with subgenus Therorhodion in the basal position, consistent with the matK studies. [42] Many species and cultivars are grown commercially for the nursery trade. Most species have brightly colored flowers which bloom from late winter through to early summer.[6]. Rhododendrons have fibrous roots and prefer well-drained soils high in organic material. Rhododendron species are used as food plants by the larvae (caterpillars) of some butterflies and moths; see List of Lepidoptera that feed on rhododendrons. Rhododendron maximum, the most widespread rhododendron of the Appalachian Mountains, is the state flower of the US state of West Virginia, and is in the Flag of West Virginia. Red-flowered varieties such as Baden Baden (Rhododendron 'Baden Baden') and Scarlet Wonder (Rhododendron 'Scarlet Wonder') stay small and are hardy down to USDA zone 6. Height, flower color and form, leaf size and form, hardiness, and flowering times vary so widely that rhododendrons defy a definitive description. Meanwhile, other botanists such as Salisbury (1796)[19] and Tate (1831)[20] began to question the distinction between Azalea and Rhododendron, and finally in 1836, Azalea was incorporated into Rhododendron[21] and the genus divided into eight sections. When it comes to the Lavender Rhododendron, there's nothing you can't do. The fastest-growing rhododendron cultivars grow 7 feet in 10 years, according to the American Rhododendron … Rhododendrons have no ultimate size, they can carry on growing indefinitely. These have been progressively incorporated into Rhododendron. Sometimes an attached branch that has drooped to the ground will root in damp mulch, and the resulting rooted plant then can be cut off the parent rhododendron. Soil preparation is best accomplished in autumn before planting the rhododendron in spring. Subgenus Tsutsusi (C) was reduced to section status retaining the name, and included in subgenus Azaleastrum. As well as being small, some varieties produce tiny leaves, such as Rhododendron impeditum, with bright blue flowers and hardiness down to USDA zone 5, or Chikor (Rhododendron 'Chikor'), hardy down to USDA zone 6, which bears clear yellow flowers. Genus Menziesa (9 species) was also added to section Sciadorhodion. Rhododendrons (Rhododendron spp.) [11] The centres of diversity are in the Himalayas and Malaysia,[40] with the greatest species diversity in the Sino-Himalayan region, Southwest China and northern Burma, from Himachal Pradesh, Uttarakhand, Nepal, Sikkim, Nagaland to northwestern Yunnan and western Sichuan and southeastern Tibet. [51] Azaleas are frequently used around foundations and occasionally as hedges, and many larger-leafed rhododendrons lend themselves well to more informal plantings and woodland gardens, or as specimen plants. Why Fast-Growing-Trees.com is Better. Older ranks such as Series (groups of species) are no longer used but may be found in the literature, but the American Rhododendron Society still uses a similar device, called Alliances[44], Species of the genus Rhododendron are widely distributed between latitudes 80°N and 20°S and are native to areas from North America to Europe, Russia, and Asia, and from Greenland to Queensland, Australia and the Solomon Islands. The remaining four subgenera contain very few species. Exbury hybrids – derived from the Knap Hill hybrids, developed by, Ghent (Gandavense) hybrids – Belgian raised, Knap Hill hybrids – developed by Anthony Waterer at the, Mollis hybrids – Dutch and Belgian raised, New Zealand Ilam hybrids – derived from Knap Hill/Exbury hybrids, Rustica Flore Pleno hybrids – sweet-scented, double-flowered, Gable hybrids – raised by Joseph B. Gable in, Glenn Dale hybrids – US raised complex hybrids, Indian (Indica) hybrids – mostly of Belgian origin, Kyushu hybrids – very hardy Japanese azaleas (to −30 °C), Oldhamii hybrids – dwarf hybrids raised at, Satsuki hybrids – Japanese raised, originally for, Vuyk (Vuykiana) hybrids – raised in the Netherlands, Azaleodendrons – semi-evergreen hybrids between deciduous azaleas and rhododendrons, This page was last edited on 13 December 2020, at 21:10. The key is the annual growth rate, up to 60cm per year for the most vigorous and less than 1cm for the slowest growing. Subgenus Tsutsusi is found in the maritime regions of East Asia (Japan, Korea, Taiwan, East China), but not in North America or Eurasia.[2][24]. The nineteenth-century American poet and essayist Ralph Waldo Emerson in 1834 wrote a poem titled "The Rhodora, On Being Asked, Whence Is the Flower", In Joyce's Ulysses, rhododendrons play an important role in Leopold and Molly's early courtship: Molly remembers them in her soliloquy – "the sun shines for you he said the day we were lying among the rhododendrons on Howth head in the grey tweed suit and his straw hat the day I got him to propose to me". It is good to start small and up-size your pot every 2 to 3 years (except if you plant to grow your rhododendron in a large pot that is not designed to be moved around). Most have been bred for their flowers, but a few are of garden interest because of ornamental leaves and some for ornamental bark or stems. Following publication of the studies of Goetsch et al. A new calcium-tolerant stock of rhododendrons (trademarked as 'Inkarho') has been exhibited at the RHS Chelsea Flower Show in London (2011). The world's tallest rhododendron in located in India, however, and reaches 108 feet in height. The American Rhododendron Society identifies fast growing rhododendrons that reach a height of 7 feet after 10 years. The hardiness range for rhododendrons falls between U.S. Department of Agriculture plant hardiness zones 4 through 8, but each rhododendron has its own hardiness rating, according to Missouri Botanical Garden. Set new plants so that their top roots are at soil level or slightly below. Rhododendrons can be propagated by air layering or stem cuttings. How to choose the substrate for growing in pots. Eleven similar cases have been documented in Istanbul, Turkey during the 1980s. Rhododendron niveum is the state tree of Sikkim in India. While usually grown as shrubs, they can get very big and take up the space of a small tree. Plant Hardiness Zones 4-8 . November 25, 2020. (2005)[2] and by Craven et al. Records of the Rhododendron Society of America reside at the Albert and Shirley Small Special Collections Library at the University of Virginia. [64] Mulching and careful watering are important, especially before the plant is established. [42] In 2011 the two species of Diplarche were also added to Rhododendron, incertae sedis.[43]. R. ponticum is the state flower of Indian-administered Kashmir and Pakistan-controlled Kashmir. Selection of cold tolerant varieties, correct placement … Like other ericaceous plants, most rhododendrons prefer acid soils with a pH of roughly 4.5–5.5; some tropical Vireyas and a few other rhododendron species grow as epiphytes and require a planting mix similar to orchids. have found that the root of the plant is able to reduce the activity of NF-κB in rats. (2005) with RPB2,[2] there began an ongoing realignment of species and groups within the genus, based on evolutionary relationships. Mature Width 8-10 . Moisture and length of growing season greatly affect rate of growth: mild wet areas may have twice the growth rate of cold dry ones. Rhododendron borers and various weevils are major pests of rhododendrons, and many caterpillars will preferentially devour them. The majority of rhododendrons fall between about 3 to 6 feet in height. Following the cladistic analysis of Goetsch et al. Unfortunately, most rhododendrons and azaleas (there are over 900 species and innumerable varieties) cannot be successfully grown in Iowa because of a lack of cold hardiness. The rhododendron bush is an attractive, blooming specimen in many landscapes and is fairly low maintenance when planted properly. Xenophon described the odd behaviour of Greek soldiers after having consumed honey in a village surrounded by Rhododendron ponticum during the march of the Ten Thousand in 401 BCE. Sleumer based his system on the relationship of the flower buds to the leaf buds, habitat, flower structure, and whether the leaves were lepidote or non-lepidote. [24] Bentham and Hooker used a similar scheme, but called the divisions "Series". Two Types of Vireya Rhododendrons. This structure largely survived till recently (2004), following which the development of molecular phylogeny led to major re-examinations of traditional morphological classifications,[16][17] although other authors such as Candolle, who described six sections,[22] used slightly different numeration. Linnaeus' six species of Azalea were Azalea indica, A. pontica, A. lutea, A. viscosa, A. lapponica and A. procumbens (now Kalmia procumbens), which he distinguished from Rhododendron by having five stamens, as opposed to ten. Varieties hardy only to USDA zone 7 can't tolerate extended cold spells, and include varieties such as Cappuccino (Rhododendron 'Cappuccino') and September Snow (Rhododendron 'September Snow'), both bearing white flowers, and Primary Pink (Rhododendron 'Primary Pink'), which bears pink flowers. [2] (See schemata under Subgenera) (Table 1. [33], A number of closely related genera had been included together with Rhododendron in a former tribe, Rhodoreae. Like this rhododendron. See Thursday Next series,[78] and Shades of Grey. Some are in big … The pot’s size is also important, it shouldn’t be too big. (2005) Table 1.[2]. [49], Rhododendron bud blast, a fungal condition that causes buds to turn brown and dry, and not open, is caused by the fungus Pycnostysanus azaleae, which may be brought to the plant by the rhododendron leafhopper, Graphocephala fennahi.[50](p562). Later Gao et al. In some areas, larger rhododendrons can be pruned to encourage more tree-like form, with some species such as Rhododendron arboreum and R. falconeri eventually growing to 10–15 m or more tall. Rhododendrons that stand 1 to 3 feet tall are often considered dwarfs. The Royal Horticultural Society is the UK’s leading gardening charity. 10 Varieties of Rhododendrons to Try in Your Yard (+ Growing Tips) Looking for an evergreen shrub that loves the shade, bears large flowers, is low maintenance and will last for decades? Individual hybrids of rhododendrons have been grafted on to a rootstock on a single rhododendron plant that was found growing in a chalk quarry. [74] The suspect rhododendrons are Rhododendron ponticum and Rhododendron luteum (formerly Azalea pontica), both found in northern Asia Minor. [45] The largest of these is subgenus Rhododendron, containing nearly half of all known species and all of the lepidote species. In addition, rhododendrons can easily be suffocated by other plants or evergreen trees that grow up around them and block sunlight. Rhododendrons up to 1 foot in size; Otherwise known as miniature Rhododendrons, these variations rarely grow above 12 inches in height. Then they will not grow into a tree or a big bush. [76] It was also mentioned in the third episode of Season 2 of BBC's Sherlock, speculated to have been a part of Sherlock's fake death scheme. [1][14] He listed five species under Rhododendron (Rhododendron ferrugineum (type species), R. dauricum, R. hirsutum, R. chamaecistus (now Rhodothamnus chamaecistus (L.) Rchb.) The large number of species that were available by the early twentieth century prompted a new approach when Balfour introduced the concept of grouping species into series. These often-broadleaf evergreen plants boast large clusters of showy blooms at their growing tips in spring. Remember, though, that many rhododendrons can grow from 20 to 30 feet tall, weaving a root system that spreads wider than the top growth, so moving smaller azaleas might be more successful. Pompey's soldiers reportedly suffered lethal casualties following the consumption of honey made from Rhododendron deliberately left behind by Pontic forces in 67 BCE during the Third Mithridatic War. Miniature rhododendrons seldom grow beyond a foot in height. On the other hand, azaleas (a type of rhododendron) represent the second Mrs. De Winter. / Landscaping / Fall Planting, Pennsylvania, Perennials. After they bloom and the flowers die, you can prune them back a little each year. (2005)[2] this scheme was simplified, based on the discovery of three major clades (A, B, C) as follows. [82] while in Scotland species are being conserved by the Rhododendron Species Conservation Group.[83]. [2], Rhododendron are characterised by having inflorescences with scarious (dry) perulae, a chromosome number of x=13, fruit that has a septicidal capsule, an ovary that is superior (or nearly so), stamens that have no appendages, and agglutinate (clumped) pollen. [53], Horticulturally, rhododendrons may be divided into the following groups:[16][54]. Subgenus Pentanthera (deciduous azaleas) with its four sections was dismembered by eliminating two sections and redistributing the other two between the existing subgenera in clades B (Hymenanthes) and C (Azaleastrum), although the name was retained in section Pentanthera (14 species) which was moved to subgenus Hymenanthes. Click to see full answer Beside this, how big do rhododendrons get? The four sections of Pentanthera between clades B and C, with two each, while Azaleastrum had one section in each of A and C. Thus subgenera Azaleastrum and Pentanthera needed to be disassembled, and Rhododendron, Hymenanthes and Tsutsusi correspondingly expanded. These scales, unique to subgenus Rhododendron, are modified hairs consisting of a polygonal scale attached by a stalk. Rhododendrons can become quite large, even tree-like. Rhododendrons are often valued in landscaping for their structure, size, flowers, and the fact that many of them are evergreen. , two were discontinued ) Table 1. [ 2 ] ( see schemata under subgenera ) ( 1... That grow up around them and block sunlight or driveways often grow as epiphytes in 1996, bright. Large and four small subgenera provides information on rhododendrons at the Albert and Shirley Special... From late winter through to early spring on Rhododendron leucaspis the flowers die, you can prune them a. Will take years to reach an appealing height North America the Royal Horticultural Society in Ireland [ ]... 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