Description: This native perennial plant is 1½-3' tall. It forms a central stem, with a few flowering side stems in the upper half. The alternate leaves are up to 4" long and 1½" wide, and either green, bluish green, or greyish green. They are broadly lanceolate to narrowly ovate, and usually clasp the stem, although smaller leaves are sessile. Their margins are smooth or slightly serrate. Both the stems and leaves are hairless, or nearly so. The flowering stems produce sprays of numerous daisy-like compound flowers that are individually about ¾-1¼" across. Each compound flower has about 15-30 lavender or light blue-violet ray florets surrounding numerous yellow disk florets, which turn reddish yellow as they age. There is no noticeable floral scent. The blooming period occurs during late summer or early fall, and lasts about 3-4 weeks. During the fall, the achenes develop with small tufts of light brown hair they are dispersed by the wind. The root system is coarsely fibrous, and has reddish rhizomes with an anise scent. Older plants may develop a branched caudex. Loose colonies of plants may form vegetatively through the rhizomes.
Cultivation: The preference is full or partial sun, and mesic conditions. This plant isn't particular about soil type it typically grows in fertile loam or clay loam. This plant remains erect while in bloom, even if it is spoiled, and withstands drought fairly well. It is vulnerable to powdery mildew and other foliar disease to a moderate extent. This is an easy plant to grow, but it sometimes has trouble competing with taller, more aggressive plants.
Range & Habitat: Smooth Blue Aster occurs occasionally in most counties of Illinois, but it is uncommon or absent in western and SE Illinois. Habitats include mesic black soil prairies, loess hill prairies, savannas, openings in upland forests and sandy forests, woodland edges, thickets, limestone glades, and roadside embankments.
Faunal Associations: The flowers attract many kinds of insects, principally long-tongued and short-tongued bees, Syrphid flies, bee flies, and the occasional butterfly or skipper. Green metallic bees are common visitors. The caterpillars of the butterfly Chlosyne nycteis (Silvery Checkerspot) feed on the foliage, while the caterpillars of many species of moths feed on this and other asters. Other insects that feed on asters include plant bugs, lace bugs, and aphids. The Wild Turkey eats the foliage and seeds to a limited extent. Various mammalian herbivores eat the flowers, foliage, and stems, including deer, rabbits, groundhogs, and livestock.
Comments: This aster has many attractive qualities, which include its adaptability, beautiful flowers, attractive foliage, and stems that remain erect during the blooming season. It's surprising that it is not grown more often in flower gardens. Smooth Blue Aster can be distinguished from other asters primarily by the lack of hairs on the smooth foliage and stems, which sometimes have greyish or bluish tints. Other asters tend to have leaves that are hairy or rough in texture. The leaves of Smooth Blue Aster often clasp the stem and are never cordate (heart-shaped), unlike many woodland asters. By placing the mouse cursor over the upper photograph, a close-up of the stem and leaves for this aster will be revealed. The white flowers in the upper photograph are from another species Aster pilosus (Frost Aster).