Iris prismatica

Common Names

Slender Blue Flag, Slender Blue Iris, Coastal Iris, Cubeseed Iris

Summary

Iris prismatica, commonly called Slender Blue Flag, is a long-lived rhizomatous perennial native to wetlands along the Atlantic coast from Georgia to Maine, forming clumps from near-surface rhizomes and possessing very narrow leaves about 3–6 mm wide, with upright flowering stems bearing two to three pale violet-blue flowers having pale violet standards and white-throated falls, the three-angled, winged seed capsule and slender habit helping distinguish it, and it grows to about 0.5–1 m tall in brackish or fresh marshes, bogs, meadows, and shores in moist soils, while cultivation favors moist, humus-rich soil that is neutral to slightly acidic, with full sun to partial shade and consistent moisture; it tolerates some salinity and is suitable for bog gardens, pond edges, or borders where soils stay moist, propagation is by division, and it is hardy in USDA zones 4–8, making it a native moisture lover that supports wildlife by providing habitat and blue blooms favored by pollinators such as bees and hummingbirds, a strong choice for rain gardens and coastal landscapes.

Lifecycle

Perennial

Height

12-36 inches

Spread

1-3 feet

Hardiness Zones

Zones 3-9

Sunlight Requirements

Ideally full sun; tolerates partial sun and partial shade.

Soil Type

Moist, humus-rich soil that is neutral to slightly acidic

Soil Drainage

Moist but well-drained soil

Soil pH

Acidic to neutral soil (pH in the acidic to neutral range)

Bloom Color

Blue

Bloom Time

Summer

Foliage Color

Green

Leaf Lifecycle

Deciduous

Growth Rate

Rapid, reaches ultimate height in 2–5 years.

Seasons of Interest

Spring and Summer

Propagation Methods

Seeds, Division (via rhizomes)

Attracts Wildlife

Attracts hummingbirds, attracts other pollinators, attracts birds