Aster cordifolium (blue wood aster) is a tough, native-style perennial for late-season color. You will get clouds of small, pale blue to violet flower heads in loose sprays from late summer into fall, often when many other perennials are winding down. The heart-shaped lower leaves give the plant a soft woodland look, and the branching stems create a light, natural texture in borders, meadows, and open shade plantings.
Plant it in full sun to part shade; more sun generally means more flowers, while part shade can help it look fresher in warmer climates. Provide average, well-drained soil and moderate moisture, though established plants handle occasional dry spells. Mature size is typically about 24-60 inches tall, with a spread around 12-24 inches depending on site and competition.
For a fuller, sturdier plant, pinch or cut stems back in late spring to early summer; this encourages branching and can reduce flopping. Taller stems may still benefit from discreet support in richer soils. After bloom, you can leave seedheads for seasonal interest and wildlife value or cut the plant back to limit self-seeding. Divide clumps if you want to refresh vigor or share plants. This aster is a reliable choice for pollinator gardens, naturalized areas, and mixed perennial borders where you want an easy fall performer.