Smooth Blue Aster

Symphyotrichum laeve

Asteraceae

• Washington State Native
• Sun - Part Sun
• Size: 2'–4' tall x 2'–3' wide
• Drought Tolerant: moderate
• Evergreen: no
• Flower Color: Lavender-blue with yellow centers (July- October)
• Wildlife value: supports 39+ lepidopteran species including the Pearl Crescent butterfly and Asteroid Moth; 31+ specialist oligolectic bee species depend on Symphyotrichum pollen; goldfinches, sparrows, and other birds eat seeds; leave seedheads standing for winter bird forage
  

Smooth Blue Aster is arguably the most elegant of all the native blue asters — a tall, architecturally refined perennial that brings true lavender-blue color to the fall garden at a season when few other plants can compete. Its native range stretches broadly across North America, including Washington State, where it inhabits fields, open woods, prairie edges, and roadsides from the lowlands into lower mountain elevations. The species takes its name from its most immediately distinguishing feature: unlike most asters, whose stems and leaves are notably rough-hairy or sandpapery, Smooth Blue Aster's stems and foliage are conspicuously smooth, often with a slight glaucous blue-green or waxy coating that gives the entire plant a polished, refined quality through the growing season. Widely native but commercially underutilized, it deserves far greater prominence in Pacific Northwest native plant gardens.

The plant produces erect, sturdy stems to four feet, branching toward the upper portions into many-flowered panicles. The leaves are alternate, smooth, blue-green, and broadly lance-shaped, clasping the stem at their base — a distinctive characteristic that aids identification. From late August through October, branch tips produce abundant clusters of one-inch composite flowers with clear lavender to violet-blue ray florets surrounding a central yellow disc that ages attractively to deep red or burgundy as the season progresses. The overall display is generous and genuinely spectacular — a well-established plant in full bloom may carry hundreds of flowers simultaneously, creating a haze of cool blue at a season when the garden's warm tones predominate. The blue-and-gold color combination is unsurpassed for late-season pollinator gardens and prairie-style borders.

Smooth Blue Aster belongs to one of North America's ecologically critical plant genera, and its wildlife relationships are correspondingly rich. The Xerces Society for Invertebrate Conservation designates Symphyotrichum species as having special value to native bees — a recognition of the extraordinary diversity of bee species that depend on aster pollen and nectar. Research documents 31 or more specialist (oligolectic) bee species that collect pollen primarily or exclusively from Symphyotrichum, as well as generalist bees representing a broad cross-section of native bee families. The plant is also a larval host for the Pearl Crescent butterfly, the Wavy-lined Emerald moth, the Asteroid moth, and numerous other lepidopteran species — with some sources documenting 39 or more caterpillar species feeding on Symphyotrichum foliage. Goldfinches and other seed-eating birds actively work the mature seedheads through winter; leaving plants standing until early spring provides essential cold-season forage.

In the Spokane garden, Smooth Blue Aster is ideal for the middle or back of a sunny perennial border, prairie or meadow planting, or naturalized wildflower garden. It stands well on its own without staking under normal garden conditions, though very rich soil or shade may encourage laxer growth; pinching stem tips in late spring encourages a bushier, more self-supporting habit. It is best massed in groups of three or more plants for full visual impact and maximum pollinator benefit. Outstanding companion plants include Undaunted Ruby Muhly Grass (Muhlenbergia reverchonii 'Undaunted') — the ruby-and-blue combination is one of fall's finest — along with Missouri Goldenrod (Solidago missouriensis), Narrow-leaved Purple Coneflower (Echinacea angustifolia), Leadplant (Amorpha canescens), Idaho Fescue (Festuca idahoensis), and Little Bluestem (Schizachyrium scoparium). The older trade name Aster laevis appears on many nursery labels and seed packets; both names refer to the same plant.