GENUS PROFILE

HOUGH ONLY Amsonia is commonly Tcultivated, the 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 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. height varies for their blue and autumn colour from 12.5cm to nearly 1.2m. The alternate 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 (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 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, 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 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 (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 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 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 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 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 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 var. tenuifolia Rick Darke hardy to USDA zone 4, yet is (syn. A. ciliata var. filifolia ) (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. This species North Carolina, South Carolina and marketed by Plant Delights Nursery appears to be highly drought-tolerant Texas, this fine-textured species is as the cultivar ‘Georgia Pancake’. and therefore holds promise for superficially similar to A. hubrichtii. Barely 12.5cm high, a single mature gardens in truly arid regions. Typical height is 60–90cm. The plant will carpet a 60cm diameter linear-lanceolate leaves are 2.5–5cm circle with bright green needle-like Amsonia jonesii long and up to 4mm wide, but rarely foliage. Tiny pale blue flowers appear Native to Arizona, Colorado, New as threadlike as A. hubrichtii. It can at the branch tips in spring, however Mexico and Utah, this is another usually be recognised by the fine their colour is surpassed in strength North American species that fringe of hairs lining the stems and by the autumn foliage, which turns deserves further attention from new leaves. This is more pronounced rich shades of gold and amber if gardeners in arid regions. It grows on some plants than others and, when plants are grown in full sun. to a height of about 30cm

74 June 2005 PlantsmanThe

Amsonia ‘Blue Ice’ propagated by stem cuttings taken in Amsonia ‘Blue Ice’ is a superb garden early summer, and this method is plant of doubtful origin and species. most appropriate for retaining the Reported to have been discovered as unique characteristics of selected a seedling in a New England nursery forms and cultivated varieties. block of A. tabernaemontana, it grows Division is the least practical method only 40cm tall and has perhaps the of propagating bluestars, since the deepest lavender-blue flowers of all woody rootstocks of mature plants the currently known bluestars. It are nearly impossible to cleave bears a superficial resemblance without a sharp spade or hatchet. to A. orientalis. Bluestars are sometimes inclined to

Rick Darke self-sow, but this is rarely a nuisance. Amsonia elliptica The one point to consider is that Another bluestar not from the US, since many bluestars readily cross- this species is native to Japan, China, pollinate, gardeners with several and Korea. It grows to a height of species growing in proximity to one 40cm and bears narrowly elliptic another may find hybrids appearing leaves and flowers to about 1cm in their plantings. Some of these may across. Some forms have particularly be distinct and worth saving but rich blue flowers but it is rare in culti- others may be inferior and discarded. vation and deserves further attention. Bluestars can be somewhat slow to reach mature size, but this is offset by Cultivation their long life in cultivation. Unlike Durable and unusually long-lived, the so many herbaceous perennials that species described here are extremely experience centre die-out after just a rewarding perennials that are of easy few years, bluestars produce strong,

RHS Herbarium cultivation. They prefer full sun or uniform growth almost indefinitely, Amsonia ciliata ‘Spring Sky’ (top) is a recent very light shade but are broadly requiring no more than cutting back introduction distinguished by its larger flowers and tolerant of soil types and ranges of to ground level for annual main- prominent leaf hairs. Amsonia tabernaemontana tenance. Since bluestars remain (above) is exceptionally hardy and the yellow autumn acidity. All will thrive in garden soils foliage develops best when grown in full sun of average moisture, but many, attractive into late autumn or especially the species native to the into winter, cutting back may Amsonia orientalis (syn. Rhazya North American south, are extremely be postponed until late winter orientalis) tolerant of droughty conditions. As a or early spring. One of the few bluestars not from group they are among the most cold- Several of the species described North America, this species is native hardy of perennials, with most here are relatively new to cultivation to NE Greece and NW Turkey. It is capable of surving winters in USDA and need further trialling. Others therefore more familiar to European zones 4. Heat tolerance is never a are better established and have gardeners than it is to those in the problem. In fact, a lack of strong proved to be superb garden plants. US. With short stature (to 45cm tall), summer sun is one of the few things Because their woody rootstocks narrowly ovate leaves to 5cm long and that can result in weak growth and prove to be tough, bluestars can be relatively deep lavender-blue flowers diminished autumn foliage colour. planted in bold sweeps and masses about 1cm across, it superficially This is something that UK growers that will define garden spaces and resembles the diminutive forms of need to be aware of. designs for decades. ■ A. tabernaemontana. It also has yellow autumn colour. The genus Rhazya is Propagation RICK DARKE, previously Curator now included in Amsonia by most Amsonia species can be grown from at Longwood Gardens, Pennsylvania, authorities but it was previously seed sown over winter or in early has authored multiple books. separated on the basis of minor spring. Seeds require cold treatment See www.rickdarke.com for further details of leaf hairs. for germination. They can also be background information

June 2005 75