The yellow flag flower, like those of other iris species, is composed of six petals: 3 outer, downward pointing ones called falls and 3 inner ones called standards.
Jack grows yellow iris along the margins of the Catfish Pond where it can survive extremes of both high (drowning) and low (high and dry) but is constrained from wandering into nearby natural areas.
Yellow flag is a robust and vigorous iris with ribbed grayish green sword shaped leaves 3-5 ft (0.9-1.5 m) long and profuse yellow flowers 3-4 in (1.2-1.6 cm) across borne on erect stems to 4 ft (1.2 m) tall. As in all irises, the flowers of yellow flag are composed of six perianth segments: three outer ones called "falls" which droop outward and down, and, alternating with the falls, three inner segments called "standards." The falls and standards of yellow flag are bright yellow with violet or brownish veins. In addition, each fall has a darker yellow-brown blotch near its base. There are usually 4-12 flowers on each branched flower stalk, and they appear in early spring. The selection, 'Alba' has cream colored flowers; 'Gigantea' has stems to 8 ft (2.4 m) tall and large golden yellow flowers; 'Variegata' has young springtime leaves striped with yellow; 'Golden Fleece' has falls and standards lacking the darker markings; 'Flore-Pleno' has double flowers. The botanical variety bastardii has very pale yellow flowers without markings.
The irises are native to temperate regions throughout the northern hemisphere in North America, Europe and Asia. Yellow flag occurs naturally in Europe, eastward to Siberia and south to northern Africa. It is an iris of wet places, usually growing in shallow water in a marsh or at the edge of a stream or pond. Yellow flag has naturalized in wet places over much of the eastern United States, and is often rather common in marshes and along streams from New England to Florida.
Culture Light: Yellow flag should be in full sun when grown in water or very moist soils. On drier sites, the plant should receive some shade from the midday sun. Moisture: Yellow flag should be kept moist. It can be grown at the margins of ponds, lakes or streams, or directly in the shallow water, where it attains its greatest size and vigor. Plants grown on drier sites should be watered frequently and can be expected to stay smaller and spread less than those grown in the water. Hardiness: USDA Zones 4 - 9. Propagation: Propagate yellow flag by division in late summer after flowering has ceased, or harvest ripe seed in fall. Seeds produce variable plants and take two years to flower. On a good, wet site, yellow flag will probably seed itself, and could become a nuisance if not restricted.
This lucky yellow flag planting enjoys a special home along the moat surrounding the Bok Tower in Lake Wales, Florida.
Yellow flag grown under drier garden conditions is smaller and is not so apt to be invasive as when planted in constantly moist soils.
Yellow flag should be grown in rich soil at the edge of a water garden or stream. It thrives in shallow water, and many gardeners plant yellow flag in a container of rich potting soil placed directly in the garden pond. Remove seed pods to prevent self seeding, as this iris will spread under ideal growing conditions.
Yellow flag has had many uses over the centuries. The dried and powdered roots were used as a snuff; the seeds were roasted and prepared like coffee; the flowers were used to make a yellow dye; the rhizomes were used as a powerful laxative. Cut flowers last well and the dried fruit capsules are very attractive in arrangements.
Irises have been bred, hybridized and selected for more than 150 years. There are some 300 species of irises and more than a thousand named hybrids and selections. The many species, hybrids and selections of irises are divided into two main groups: rhizomatous and bulbous. The rhizomatous irises are further divided into three groups: bearded, with a tuft of hairs near the base of each fall; crested (a.k.a. Evansia), with a raised crest where the beard would be; and beardless. Yellow flag is one of the rhizomatous beardless irises. The genus is named for the Greek goddess, Iris, who walked on the rainbow between heaven and Earth, leaving colorful flowers in her footsteps. Yellow flag is probably the model for the "Lily of France" emblem of the French kings, in use since the 12th century.
Yellow flag could spread and dominate a wetland site if allowed. It has become established in natural areas in North America, but apparently has not become a problem severe enough to be placed on restricted plant lists - yet. Do not plant yellow iris in natural bodies of water or anywhere it might escape into the wild.