Amsonia in Cultivation
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GENUS PROFILE HOUGH ONLY Amsonia tabernaemontana is commonly Tcultivated, the genus Amsonia contains 22 species, most of which have horticultural merit or potential. The majority occur in a wide range of habitats throughout central, southern and eastern North America. A few others are native to southern Europe, Turkey, Japan, Korea and China. The genus is named for Dr John Amson, an English physician who settled in Virginia in the mid 1700s, where he became friends with John Clayton, a British botanist celebrated for his work with New World flora. Renewed interest in North American native species in recent years has resulted in perhaps a dozen Rick Darke Amsonia species now being available from specialist US nurseries and about half that in the UK. A number of distinct botanical varieties and Amsonia cultivars are also offered. In the US they are commonly known as bluestars. in cultivation Genus characteristics Amsonia is a genus of clump-forming RICK DARKE assesses a genus of herbaceous herbaceous perennials with multiple perennials that contains a range of species grown leafy stems growing from a semi- woody rootstock. Plant height varies for their blue flowers and autumn colour from 12.5cm to nearly 1.2m. The alternate leaves are entire and range (follicles) up to 10cm in length. bluestars have many other in shape from broadly ovate, up to Like most other members of the characteristics that make them 2.5cm wide, to linear and needle-like Apocynaceae (dogbane family), among the best garden perennials. to only 2mm wide. In spring and early Amsonia species have milky sap. Most would be worth growing for summer the flowers are borne in Although the sap of some relatives foliage alone. All bluestars produce terminal panicled or corymbose such as Nerium contains highly toxic masses of rich green leaves that cymes. The individual flowers, up to alkaloids, the sap of Amsonia is remain neat and attractive 1.5cm in diameter, have funnel- relatively innocuous. It is not known throughout the growing season, shaped corollas with five sharply to be harmful to humans but does generally free from any insect pests. pointed, spreading petal lobes, and seem to discourage predation by deer The broad leaves of larger species are star-like in overall appearance. and other mammals – a good thing such as A. tabernaemontana result in Ranging from very pale to rich sky for many gardeners. a bold-textured presence that adds blue, flower colour is most drama to any design, while more concentrated in bud stage and Garden use thread-leaved species such as sometimes fades to near-white when A sweep of star-like sky-blue flowers A. hubrichtii are so soft-textured as fully opened in strong sunlight. Seeds in spring is certainly an appealing to appear cloud-like – even finer than are produced in cylindrical capsules sight but, pretty as their flowers are, many grasses. The height and density 72 June 2005 PlantsmanThe This variant is distinct and valuable from a horticultural viewpoint and the current trend in nurseries has been to refer to it as A. tabernaemontana ‘Montana’. A related selection, only 25cm tall, has recently been marketed by Plant Delights Nursery, North Carolina, as ‘Short Stack’, again, best listed as a cultivar of A. tabernaemontana. Amsonia tabernaemontana var. salicifolia This variety differs from the typical species in its narrower, consistently lanceolate, glabrous leaves giving it a willow-like appearance. Rick Darke Amsonia illustris Amsonia hubrichtii (left and above), here growing in the author’s garden, was unknown to most gardeners This native of southeastern North ten years ago. It is now widely grown in the US and is becoming increasingly available in the UK. As with America occurs naturally in Arkansas, many species of Amsonia it has particularly vibrant autumn colour that can last for a month or more Kansas, Missouri, Oklahoma and of the larger species allows them to 7.5–10cm long, up to 2.5cm wide and Texas. Named for its exceptionally function almost like shrubs during often finely hairy beneath. The shiny leathery leaves, it is otherwise the growing season, while others such foliage reliably turns a pleasing light very similar in appearance to as A. ciliata var. tenuifolia are low yellow in autumn, but is never as A. tabernaemontana, and in fact enough to be used as groundcover. brilliant as A. hubrichtii. The pale blue many very lustrous-leaved plants In addition to their spring and flowers are 1–2cm across and appear offered commercially as summer appeal, many bluestars from mid-spring to early summer, A. tabernaemontana are actually develop vibrant yellow and gold depending upon situation and the A. illustris. It also differs in its hairy autumn foliage colour when grown in variability of individual seedlings. as opposed to hairless calyx. warm sunny situations. The colour of Some plants possess a light sweet some, including A. hubrichtii, rivals fragrance, though none have yet been Amsonia ludoviciana the best trees and shrubs. commercially selected for this quality. Once believed to occur naturally only It performs well in a wide range of in southern Louisiana, this species has Amsonia tabernaemontana soils, from droughty sands to heavy since been reported in Georgia, The most commonly encountered clays, but does best in moderately Mississippi and South Carolina. It is bluestar, this species occurs naturally organic, moisture-retentive soil. It distinguished by the white woolly in moist, partly sunny habitats in will withstand full sun, but is also at undersides to the elliptic leaf blades. eastern North America. Mature home in light or partial shade, and plants form an upright mound to can be an effective addition to the Amsonia hubrichtii 90cm tall with equal spread. There deciduous woodland garden. It is Though the preceding are fine garden is considerable variation in leaf width cold-hardy to USDA zone 3. plants, this species is truly distinct and foliage texture, so much so that Amsonia montana is a name of no and extraordinary, and represents the botanists and horticulturists have botanical standing that appears in most dramatic and important recent often disagreed about whether the many horticultural reference books addition to the garden palette of variation is enough to warrant and in innumerable nursery bluestars. Ten years ago it was an dividing this species into separate catalogues. It is associated with a obscure collector’s plant and today it species or varieties. The lanceolate low-growing (to 60cm tall), small- is increasingly available through retail to broadly elliptic leaves are typically leaved form of A. tabernaemontana. nurseries in the US and UK. ➤ June 2005 73 GENUS PROFILE Native only to the Ouachita well developed, adds significantly to mountains of Arkansas and Oklahoma, the plants’ appeal by glowing when this exceptional plant was only back-lit or side-lit by the sun. The discovered in 1942 by Leslie light-blue flowers, 1.2cm across, are Hubricht, a specialist in fresh water held in clusters that tend to be held molluscs, and named in his honour. higher above the foliage than in the Mature plants have more than 50 other cultivated species, and are stems, forming a broad-spreading among the showiest of all bluestars. It (to 1.2m wide) billowy mass of the requires a sharply drained, relatively finest texture. The leaves are truly infertile soil for best performance and thread-like, up to 7.5cm long and should be placed in full sun or very less than 2mm wide, and are extra- light shade. Cold hardy into USDA Flora-Pix Michael Comb ordinarily numerous and closely zone 4, this species has exceptional spaced along the 60–90cm tall stems. heat and drought tolerance. In spring the stems are topped by a Plants of this species collected in multitude of sky-blue flowers lasting the wild by botanist Mary Henry about 2–3 weeks. Summer foliage is a have proved durable in cultivation rich medium green. When grown in for half a century at her Gladwyne, strong sunlight, the peak season for Pennsylvania property, now the this species is autumn, when the Henry Foundation for Botanical stems and leaves turn a vibrant gold Research. An especially large- that endures for a month or more. flowered, ciliate form is being By the beginning of winter the colour vegetatively propagated and has turned to a dark honey-brown, introduced to cultivation as and the leaves gradually begin A. ciliata ‘Spring Sky’. dropping as winter proceeds. This species has proved cold Amsonia ciliata var. tenuifolia Rick Darke hardy to USDA zone 4, yet is (syn. A. ciliata var. filifolia ) Amsonia orientalis (top), native to the Old World, is unfazed by the summer extremes of Only 30cm or less in height, this one of the more familiar species to European gardeners. Amsonia ciliata var. tenuifolia (above) heat and drought. It thrives in a wide lower-growing, finer-textured variety has exceptionally narrow leaves and is shorter in range of soils from sands to clays, and of A. ciliata is native to sandhills, height than most other North American species seems capable of thriving in both pine barrens and rocky shores, from acid and alkaline conditions in the Georgia to Texas and Mexico, north Amsonia peeblesii US. In the UK one report suggests it to North Carolina and southern Native only to Arizona, this relatively may prefer acid soil. Missouri. A nearly prostrate variant obscure species has recently been of this variety was discovered by introduced to cultivation. It grows to Amsonia ciliata botanist Bob McCartney in the a height of 40–90cm, has narrow, Occuring naturally on sandy soils in sandhills of Georgia’s Wheeler linear leaves, pale blue flowers and Alabama, Arkansas, Florida, Georgia, County, and has been recently yellow autumn colour.