Blue in the Sun
This article will present several sun-loving plants in various shades of blue that capture the imagination: sky blue, midnight blue, periwinkle blue, blue mist, blue ice, storm cloud, and indigo. To enjoy the beauty of blue throughout the gardening season, consider a spring-bloomer, a late spring/early summer bloomer, and then a late summer/fall bloomer. The first two plants are native to North America; the last is a nonnative from Asia.
Amsonia, commonly called blue star, is a genus of about 20 species named in honor of 18th century Virginia physician, Dr. Charles Amson. It is native primarily to North America with one species in East Asia and another in the eastern Mediterranean. This article will focus on those species native to the U.S. This clump-forming perennial has narrow, alternate leaves and clusters of blue, 5-petaled flowers. The light blue flowers are followed by elongated, pod-like fruits containing hard, black seeds which can be used for propagation. Amsonia offers three-season interest: showy, long-lasting blooms in spring (mostly in May); threadlike green foliage in summer; and yellow foliage in fall.
Of the family Apocynaceae (dogbane), members typically have milky or viscous sap that can be loaded with highly toxic alkaloids. The latex sap is mildly irritating and is not considered to be harmful to humans, although people with latex allergies are advised to wear gloves. The sap makes the plant unappealing to foraging deer, rabbits, and many garden pests.
Other members of the Apocynaceae family include periwinkle (Vinca), oleander (Nerium oleander), and the reclassified milkweed family (Asclepiadoideae), now considered a subfamily of the dogbane family.
Although it prefers moist, loamy soil, this plant can be grown in most well-drained soils, tolerating clay soils very well. Once established, it is drought resistant. Amsonia thrives in full sun to part shade. When grown in full sun, plants often require no pruning or staking. When grown in partial shade and/or in rich soils, plants tend to become more open and floppy and often require staking or pruning. Full sun promotes a brighter golden foliage color in the fall. Shade protection from the midday sun in hot climates promotes longer-lasting blooms. For a neater appearance, particularly for shade-grown plants, consider cutting back stems by 1/2 to 1/3 after flowering to promote bushy growth and a more rounded foliage mound. The dwarf cultivars do not require staking or cutting back. Moderately drought-tolerant once established, this is a low maintenance, easy-to-grow, long-lived plant not subject to disease or pest problems.
Many insects enjoy the nectar of amsonia flowers, especially long-tongued insects such as carpenter bees, hummingbird moths, and butterflies. Ruby-throated hummingbirds are also attracted to the nectar.
The range of plant sizes makes amsonia a versatile choice in the garden. Tidy foliage and a striking vase-shaped growth habit allow bluestar to perform well as either an accent plant or in mass plantings. It is an excellent addition to a pollinator garden, native garden, deer-resistant garden, butterfly nectar garden, cottage garden, water-wise landscape, low maintenance planting, meadow, or prairie garden. Smaller varieties work well in containers.
The plant can be propagated from stem cuttings taken after flowering. Propagation by seed is possible, but lengthy. It first requires a stratification process. Seeds then take about 10 weeks to sprout and seedlings may not be ready to transplant for about 20 weeks. Although plants rarely need to be divided for overcrowding or rejuvenation, propagation by division is fairly easy. Divide plants in late summer or early fall to ensure that the divided plants develop roots before the ground freezes. Cover with a winter mulch to prevent newly divided plants from heaving during the freeze-and-thaw cycles.
Commonly called eastern blue star, bluestar, blue dogbane, or willow amsonia, this native is found in central and eastern U.S. from New York to Florida. It has light blue flowers. Dense foliage is lime green when it first appears and then turns dark green. The lance-shaped foliage is coarser and larger than that of A. hubrichtii.
A. tabernaemontana ‘Short Stack’ is a dwarf cultivar that grows to only 10-12” tall and 18” wide. It has sky-blue flowers. This cultivar may be subject to rust.
A. tabernaemontana ‘Storm Cloud’ features near-black stems with silver-veined dark green leaves in spring which lighten to olive green by summer. Light periwinkle-blue flowers bloom from late spring to early summer, often with some rebloom thereafter. It may be subject to rust.
Amsonia ‘Blue Ice’ is very similar in appearance to A. tabernaemontana, except that it is much more compact, growing to 1.5’ tall and wide. Its flowers are dark lavender-blue. In a Chicago Botanical Garden plant evaluation, ‘Blue Ice’ was awarded a 4-star rating. Although ‘Blue Ice’ was reportedly discovered growing with A. tabernaemontana seedlings in a greenhouse at White Flower Farm, the parentage has apparently not yet been definitively determined.
Amsonia ‘Seaford Skies’ is a bluestar hybrid (A. hubrectii x A. tabernaemontana) that was discovered growing in a private garden in Seaford, Virginia. Averaging 2-4’ tall and 2-3’ wide, it can grow as tall as 5 feet. It features sky blue flowers atop 36” erect stems.
A. tabernaemontana var. salicifolia
Commonly called bluestar, this perennial is native to the southeastern U.S. in zones 3-9, so it is somewhat winter hardier than other amsonias. It prefers moist, loamy soils but can also tolerate clay. It has some drought resistance. Its flowers are light blue with white throats.
Commonly called Ozark bluestar or shining blue star, this Missouri native has light blue flowers. Although very similar in appearance to A. tabernaemontana, the leaves of A. illustris are shinier, thicker, and more leathery and the seed pods are pendant. The plant grows 2-3’ tall and 1-1.5’ wide.
Commonly called bluestar, Arkansas amsonia or Hubricht’s amsonia, this uncommon perennial is native to central Arkansas. The feathery foliage of A. hubrichtii is significantly different from the broad leaves of A. tabernaemontana. It is also narrower and more thread-like than the needle-like leaves of A. ciliata and lacks that species’ conspicuous hairiness. Powdery-blue flowers appear in April to May.
Specific epithet is in honor of Leslie Hubricht, an American biologist and malacologist (mollusks) who first discovered this amsonia species growing in the wild in the early 1940s. Mr. Hubricht worked as an assistant at the Missouri Botanical Gardens from 1936 to 1943.
Commonly called blue star, fringed blue star, or downy amsonia, this perennial is native to the southeastern U.S. The specific epithet, ciliate, means hairy-margined in reference to the fringe of hairs found on new leaves and plant stems. It has narrow almost needle-like green leaves. Its flowers are pale blue. Consider cutting stems to 8-10” after flowering.
Another beautiful, shrubby, spring-blooming perennial with purple-blue blossoms is commonly called blue false indigo. It is native to the eastern and mid-western areas of the United States. Depending on the cultivar, blue false indigo typically blooms for about three to six weeks in late spring to early summer. Attractive blue-green, trifoliate foliage adds pleasing color and texture to the landscape even after the flowers have long disappeared. It grows 3-4’ tall and wide so provide ample room in your garden. This sun-loving plant is low maintenance, has few pests and diseases, and is not bothered by deer and rabbits! It also provides nectar to a variety of butterflies and pollinators. For detailed information on adding this stunning plant to your garden, see the May 2015 issue of The Garden Shed.
There is also a smaller version, Baptisia australis var minor, that grows 1.5-2’ tall and wide. Var. minor appears to differ from the species primarily by being a smaller plant with shorter stems and shorter leaves but larger flowers. The average inflorescence is about 18” long. The bloom period is in late May-June and lasts for about 3 weeks.
For plant trials and comparative results on various cultivars of Baptisia australis, refer to the Mt. Cuba Center. Baptisia australis is currently undergoing plant evaluation trials at the Chicago Botanic Garden.
Native to eastern and southern Asia, of the family Lamiacaea (mint), most plants in the genus Caryopteris are woody shrubs. Though several Caryopteris species are grown in botanical gardens as ornamental plants, the species have largely been superseded in home gardens by the hybrid Caryopteris × clandonensis (C. incana × C. mongholica). The hybrid, commonly called bluebeard, blue spirea or blue mist, originated from a chance seedling in an English garden in 1933. It was first introduced to the United States in the 1960s and soon became a garden favorite. Although not listed as invasive on the USDA Plants Database, Introduced, Invasive, and Noxious Plants, it should be watched for invasive properties because of its more recent introduction into U.S. landscapes.
Bluebeard is a low-mounded, deciduous shrub with an average height and spread of 2-3’. It is valued for its aromatic foliage and fragrant flowers which are said to resemble clouds of blue smoke or mist from late summer to early fall. The lance-shaped leaves are opposite, gray-green, and have serrated margins. Some cultivars offer variegated foliage. Roots are cold-hardy to zone 5; expect winter die-back of woody stems in climates colder than USDA Zone 7.
Caryopteris should be planted in moist, well-drained soil and exposed to full sun in order to maximize blooms. It can happily exist in light shade where it is more drought tolerant although it will not bloom quite as prolifically. Over-watering will cause root rot. Too much fertilizer may result in vigorous growth but fewer blooms. Because the flowers appear on new growth it is best to cut the shrub back to at least one-third or one-half its height in early spring. This pruning will encourage a more robust blooming season each year and serve to keep the plant’s growth habit well formed. Bumblebees, butterflies and hummingbirds are attracted to the flowers. Its aromatic leaves make it unappealing to both deer and rabbits!
Because of its compact size and mounded habitat, caryopteris adds structure to the garden as a specimen plant. Its lance-shaped foliage contrasts nicely with broadleaf plants and its profusion of blooms offers a striking focal point. The accompanying photo shows C. x clandonensis ‘Longwood Blue’ in a cottage garden with the annual, Zinnia elegans ‘Tudor’™, and perennials: Rosa ‘Radyod’ BLUSHIING KNOCKOUT; Hylotelephium ‘Herbstfreude’ AUTUMN JOY (stonecrop); and Dianthus ‘Feuerhexe’ FIREWITCH.
Caryopteris x clandonensis Cultivars
‘Dark Knight’ has deep bluish-purple flowers; ovate to lance-shaped, dull green leaves are silvery below.
‘Longwood Blue’ is a taller cultivar which may reach a height of 4′. It features a profuse, shrub-covering bloom of violet-blue flowers.
‘Arthur Simmonds’ was judged to be the hardiest cultivar of Caryopteris in the Ornamental Plant Evaluation trials at the Chicago Botanic Garden. It has violet-blue flowers.
‘Blue Mist’ has powder-blue flowers.
‘Summer Sorbet’ is a variegated cultivar that is noted for its green leaves with gold edging and its blue flowers.
C. × clandonensis ‘Durio’ Pink Chablis™ is prized as a landscape addition for its pink flowers unique to bluebeards and for its attractiveness to insect pollinators. Discovered in 1998 as a chance seedling in a Louisiana garden, it has been the subject of studies by the Dept. of Defense Deployed War-Fighter Protection (DWFP) research program. The essential oils of Pink Chablis™ have been investigated for chemical composition and bioactivity as a repellent and larvicide against the yellow fever mosquito (Sedes aegypti). It exhibited mild repellency compared to DEET and weak activitiy as a mosquito larvicide. The essential oils of its parent species have also been studied for use as insect repellents.
Each of these three sun-loving plants offers: a substantial shrubby presence in the garden; attractive foliage with interesting texture; resistance to deer and rabbits; and low susceptibility to pests and diseases. They are all good candidates for pollinator gardens since they attract butterflies, bees, and hummingbirds. The availability of cultivars offers a wide range of “blueness” that complements many other flower colors including pinks, yellows, whites, and reds. In addition, using a combination of all three plants will promote bloom for a good portion of early spring through fall!
Specific Plant Information by Name, Missouri Botanical Garden Plant Finder, http://www.missouribotanicalgarden.org/plantfinder/plantfindersearch.aspx
Specific Plant Information by Name, Lady Bird Johnson Wildflower Center Plant Database, https://www.wildflower.org/plants/
Piedmont Natives – Plant Database, https://www.albemarle.org/nativeplants/
Bluestar, Amsonia Tabernaemontana, Illinois Wildlife Federation, https://www.illinoiswildflowers.info/woodland/plants/bluestar.htm
Amsonia ‘Blue Ice’, Plant Evaluation, Chicago Botanic Garden, http://perennialsinfocus.com/snapshots-a-d/
Willowleaf bluestar, Amsonia tabernaemontana, https://wimastergardener.org/article/willowleaf-bluestar-amsonia-tabernaemontana/
“Eastern Blue Star,” The Morton Arboretum, https://www.mortonarb.org/trees-plants/tree-plant-descriptions/eastern-blue-star
Plant Evaluation, Chicago Botanic Garden, https://www.chicagobotanic.org/collections/ornamental_plant_research/plant_evaluation
“Plant Evaluation Notes: An Evaluation Study of Hardy Amsonia,” https://www.chicagobotanic.org/downloads/planteval_notes/no18_amsonia.pdf
“Baptisia australis: Both Beautiful and Indestructible!” The Garden Shed, https://piedmontmastergardeners.org/article/baptisia-both-beautiful-and-indestructible/
Baptisia, Mt. Cuba Center, https://mtcubacenter.org/trials/baptisia/
Baptisia australis var.minor, Mt. Cuba Center, https://mtcubacenter.org/trials/baptisia/baptisia-australis-var-minor/
USDA Plants Database, Introduced, Invasive, and Noxious Plants, https://plants.usda.gov/core/profile?symbol=CACL7
“April: Blue Mist Spirea Caryopteris x cland0nensis and its Cultivars, Santa Fe Botanical Garden, https://santafebotanicalgarden.org/april-2013/
For insect repellent research, google: C. x clandonensis ‘Durio’ Pink Chablis™ Research Gate