GLENCOE, Ill. (June 6, 2013) – Seven species of the classic fall-flowering aster have received top five-star ratings and 19 additional types of asters have received four-stars in Plant Evaluation Notes Issue 36, 2013, recently released by the Chicago Botanic Garden.
“Along with goldenrods, asters are classic autumnal flowers of gardens, roadsides, and native landscapes,” said Richard G. Hawke, plant evaluation manager. “They are wonderful companions to a variety of other late-season perennials and grasses.”
Asters’ hues blend beautifully with a fall garden tapestry, Hawke said, and
the plants can be peppered through a landscape, planted in large sweeps and used in mixed containers for seasonal displays. Certain types have become popular replacements for fall mums. The Chicago Botanic Garden has identified standout performers in this large and diverse plant family to help gardeners select asters best suited to the Upper Midwest.
The Garden evaluated 119 different asters grown in full sun and partial shade between 2003 and 2009 for ornamental traits—such as bloom period, flower coverage, plant height and width—and the ability to withstand harsh winter conditions. Key metrics included resistance to mildew and rust, diseases that commonly weaken plants and limit flowering times.
The aster—a name derived from the Greek word for star—belongs to the Asteraceae or daisy family, notable for its complex floral structures. Aster flowers are composed of numerous tiny florets that create a central disk and surrounding rays to give the appearance of one large single flower. The disk contains up to 300 tubular florets that can be yellow, orange, brownish, purple and occasionally white. The ray florets have one long petal-like ligule and can be varying shades of pink, red, lavender, blue, violet, purple and white.
Aster leaves vary in shape, color and texture, and plant size ranges from less than a foot to more than 6 feet tall. Some species are known to spread aggressively, and many garden asters lose their lower leaves during the hot summer months, resulting in bare lower stems. Gardeners can mask dying leaves with strategic placement of surrounding plants. Asters generally grow best in moist well-drained soils and prefer plenty of sunlight. Taller plants may require staking, especially in partially sunny or exposed windy sites. The plants—particularly New England aster (Symphyotrichum novae-angliae) and New York aster (Symphyotrichum novi-belgii)—are also prone to foliar diseases such as rusts and powdery mildew.
Here’s a look at the top-rated asters:
- Jindai (Aster tataricus ‘Jindai’) is a somewhat enigmatic garden aster with large, coarse basal leaves that grow nearly 2 feet long and are reminiscent of horseradish. ‘Jindai’ makes a good massing plant due to its vigorous clumping tendencies. Flower stems begin growing in August and eventually reach up to 4 feet tall. Lovely violet-blue and yellow flowers open in late September, and those grown in the Chicago Botanic Garden continue blooming well into late November or early December. ‘Jindai’ is a wonderful late-season aster with a distinctive habit.
- White wood aster (Eurybia divaricata) is one of the few asters that grow well in shady gardens, though plants will flower more profusely with morning sun. Smallish white flowers with yellow centers bloom from early August to early November, and are borne on dark burgundy, wiry stems. The mounded, bushy habit can create pleasing drifts in high-shade landscapes.
- Eastern star (Eurybia divaricata ‘Eastern star’) closely resembles the white wood aster but features larger flowers, darker green leaves and slightly shorter growth, with arching dusky stems that are slightly more recumbent.
- Snow Flurry (Symphyotrichum ericoides ‘Snow Flurry’) is notable for low, arching stems that create undulating mounds 8 inches tall and nearly 4 feet wide. The mat-forming habit makes a great ground cover and will cascade over walls or containers. White flowers resembling snow blanket the plants in September and October. The plant is notably disease-free and tolerates dry conditions.
- Calico aster (Symphyotrichum lateriflorum) has a graceful habit characterized by wiry stems ending in horizontally arched branches. The upper sides are covered with sprays of small white blossoms in late August to mid-September. New leaves emerge bronze but quickly fade to dark green.
- Lady in Black (Symphyotrichum lateriflorum ‘Lady in Black’) grows in a similar bushy vase-like shape, but it is slightly more compact. The foliage remains strongly purple all summer and provides the best color when grown in full sun. The central disk flowers bloom yellow but change to a purplish pink that’s particularly pleasing against the foliage.
- Raydon’s Favorite (Symphyotrichum oblongifolium ‘Raydon’s Favorite’) produces an abundance of blue-purple flowers over a long blooming period that begins in early August. A billowy habit gives the plant an informal look suited well to mass plantings and naturalizing.
The Chicago Botanic Garden’s Plant Evaluation Notes provide the latest information on plants suited to the Midwest climate and growing conditions. To download a PDF of Issue 36, “A Comparative Study of Cultivated Asters,” visit www.chicagobotanic.org/research/plant_evaluation.