Iris versicolor claims a wide native range, from Nova Scotia south through the northeastern United States to Virginia, and the specific epithet versicolor — many-colored — captures the variation across that range. The common name flag comes from the old English word flagge for reeds, an acknowledgment that this plant belongs to the water's edge as much as any rush or sedge. The blooms are blue-lavender to near-white, formed of three upright inner standards and three distinctly patterned falls, rising above clumps of narrow, strap-like leaves that reach two to two and a half feet tall. Plants will grow in up to four inches of standing fresh water and are most at home in pond margins, wet meadows, and marshy ground where they spread by rhizomes to form dense colonies.

In the garden, it performs best in full sun with rich, consistently moist to wet soil, though it tolerates partial shade with some reduction in flowering. Containers submerged in ponds or water features work well, and it is well suited to rain gardens and low-lying damp areas. Deer leave it alone. Division after bloom is the preferred means of propagation, and the plant generally requires little other attention. Aphids, iris borer, and thrips are occasional concerns; the more serious disease problems — bacterial soft rot, crown rot, rhizome rot — are typically symptoms of poor drainage rather than causes in themselves, so siting carefully pays dividends over the long term.