Blue-Eyed Grass (Sisyrinchium angustifolium)

Not actually a grass, but in the iris family, with 1/2″ light purple-blue 6-petaled flowers blooming in late spring.  Will colonize readily via self-sowing in the right conditions.  Hight: 10-18″.  Prefers moist sites, but adaptable.

$24 for 3 pots, Massachusetts supplier.

_{images from Arthur Haines, Native Plant Trust/Go Botany and Jem}