Iris Yellow Flag

Iris pseudacorus

Characteristics

Culture

Iris Yellow Flag is easily grown in average, medium to wet soils in full sun to part shade. Best performance is in acidic, saturated, moisture-retentive soils. Plants thrive in standing water (to 12” deep) where they prefer full sun. Plants grown in garden soils prefer some afternoon shade. Plants will naturalize easily by spreading rhizomes and self-seeding to form large colonies, sometimes to the point of being considered weedy and aggressive. Iris Yellow Flag plants may be grown in containers that are sunk directly to the rim in water gardens. Although plants prefer constant moisture, they grow surprisingly well in average garden soils, albeit less vigorously. Soils should never be allowed to dry out. Remove seed pods before they mature to prevent any unwanted self-seeding. Seeds that mature and drop into water can float to other locations.

Noteworthy Characteristics

Iris pseudacorus, commonly called yellow flag, is a rhizomatous beardless wetland iris that is native to Europe, northern Asia, the Middle East and northern Africa. It has naturalized in much of North America, particularly in the eastern U.S. It is at home in wet soils, typically forming large colonies along streams, ponds and marshes. It grows in expanding clumps to 3-4’ (less frequently to 5’) tall and to 30” wide. Bright yellow flowers (3-4” across), with a darker yellow zone and brown or violet veining on each fall, bloom in late spring to early summer on rigid, upright, branched stalks. Each flower stalk bears 4-12 flowers. Flowers give way to large seed pods. Sword-shaped, gray green leaves (1 1/8” wide). Plant roots have been used in the past for a variety of purposes including medical treatments, dyes, inks, and snuff. Plant seeds have been used as a coffee substitute (no caffeine however).

Problems

No serious insect or disease problems.

Garden Uses

This is an easy-to-grow plant that produces beautiful flowers. It is a good choice for moist boggy areas of water gardens including standing water. It is also effective in moist meadows, along ponds or in other high moisture areas of the landscape. Plants will perform well in borders as long as soil moisture requirements can be met. Yellow flag should not be planted along streams or ponds or lakes where it can spread into natural waterways and wetland areas.  Seed pods are valued for dried flower arrangements.