Varieties of Perennial Irises

Major Iris Species

• Irises are a large genus in the Iridaceae family, whose members also include gladiolas (Gladiolus spp.), crocus (Crocus spp.) and freesias (Freesia spp.). Estimates of iris species run to 300 and more, and irises grow on every continent. Depending on variety, most native and cultivated irises grow in USDA zones 3 through 10, with African iris (Dietes vegeta) hardy into USDA zone 11. Nearly 30 varieties are native to North America. Hybridized from seed, irises are grown from corms, bulbs or fleshy rhizomes. With a few exceptions, irises do best in mildly acid, mildly alkaline or neutral, well-drained but moist soil, with six or more hours of sun a day. Water needs are specific to variety, ranging from the moderately dry soil needs of bearded iris (Iris germanica) to the standing-water adaptability of Louisiana iris (Iris fulva) and Southern blue flag (Iris virginica). Humid weather increases susceptibility to fungal infections, and root borer plagues irises in the East and Midwest. Four large species are readily available to most home gardeners: bearded, Siberian (Iris sibirica), Japanese (Iris ensata) and Louisiana iris.

Bearded Iris

• Bearded iris varieties are generally ranked in six categories by height, from tall bearded, at 27.5 inches or more, to miniature dwarf, reaching only 8 inches in height. Hardy within USDA zones 3 through 10, bearded iris customarily bloom in late spring, with growing popularity of varieties that rebloom in fall. Shell-pink "Beverly Sills," bronzy "Cable Car" and "Grandma's Purple Flag" illustrate bearded-iris diversity. Blue "Victoria Falls" blooms several times a year in USDA zones 9 and 10. Bearded irises benefit from good air circulation; overwatering is a frequent cause of disease. Decreased bloom signals overcrowding; divide clumps of bearded iris every three or four years.

Siberian Iris

• One of several popular beardless varieties, Siberian iris has a high tolerance for heavy, wet soils in USDA zones 3 through 9. A clumping, grassy-leafed iris, Siberian is best known in its intense blue and purple versions. Purples range from pinkish "Eric the Red" to regal "Caesar's Brother." Siberian iris is relatively disease- and pest-free; unlike some other varieties, Siberian seldom requires dividing to restore blooming capacity. Siberian iris also tolerates partial shade.

Japanese Iris

• In Japan, shobu, or Japanese iris, customarily blooms around May 5, Children's Day. Their spiky leaves are strongly associated with the simultaneously celebrated Boys' Festival. Throughout USDA zones 4 through 9, this variety features lush flower shapes and sword-shaped leaves on plants about 3 feet high. Most growers advise dividing clumps every three years to maintain bloom quantity. Japanese irises favor constantly moist, even marshy, soil and can be grown on the edges of ponds or streams. They are sometimes therefore confused with Asian water iris (Iris laevigata), which has similar large, flattish flowers but grows in several inches of water. Many hybrid varieties of Japanese iris are white-variegated, with varying numbers of petals, or falls. Six-fall "Sunrise Ridge" is predominantly violet, while frilly, 9-fall "Blushing Snowmaiden" is violet-tinged. Blue "Cascade Rain is a 3-fall flower in the classic shape, resembling Mount Fuji.

Louisiana Iris

• Louisiana iris is hardy over a narrower range of USDA zones, 6 through 10, and in USDA zones 4 and 5 with winter protection. A blend of five native varieties, Louisiana hybrids offer a riot of colors and floral shape choices. Southern spring bloomers, they may bloom as late June or early July in northern climates. A decade's-worth of prize-winning Louisiana hybrids includes lilac, orange, copper, blue, purple, magenta and dark red flowers, in a multitude of petal configurations. "Praline Festival" has greenish-copper double petals, while "Hot and Spicy" resembles a green-centered, dark orange day lily. The mottled purple falls of "Henry Rowlan" perch like butterfly wings on a stem. Louisiana prefers an acid soil (pH of 5.5) rich in organic material and tolerates marshy conditions as well as regular garden beds. Partial shade and consistent moisture keeps foliage green year-round in frost-free zones.