Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
4/30/01
Contacts:
Richard Jauron, Horticulture Extension, (515) 294-1871,
rjauron@iastate.edu
Elaine Edwards, Continuing Education and Communication
Systems, (515) 294-5168, eedwards@iastate.edu
Yard and Garden Column for the Week Beginning May 4
Irises for the Home Landscape
By Richard Jauron
Extension horticulturist
Iowa State University Extension
There are more than 200 species of iris. Most irises grow from thick, underground stems or rhizomes. A few species are bulbous. An iris flower typically consists of six segments. The three inner segments, which are generally upright, are referred to as standards. The drooping, outer three segments are known as falls.
Bearded irises are one of the most popular and widely grown perennials in the home landscape. Though not as widely grown, several other types or species of iris also are attractive additions to the perennial garden. By selecting and planting several different iris species, gardeners can enjoy blooming irises from April through July.
Bearded Iris
The common name comes from the fuzzy growth or "beard" which runs down the center of each fall. Bearded irises are commonly classified into dwarf bearded (plants are 4- to 10-inches tall), standard dwarf bearded (10- to 15-inches tall, sometimes called Lilliputs), intermediate bearded (15 to 28 inches), and tall bearded (more than 28 inches). Bearded irises are available in a wide range of colors, including white, yellow, orange, pink, wine-red, blue and purple. The flowers of many varieties possess various combinations or blends of these colors. Bearded irises bloom in early to late spring. The dwarf-bearded forms are the first to bloom, usually mid-April to early May. The last of the bearded irises to bloom are the tall-bearded varieties. They usually bloom from mid-May to mid-June. Leaves are strap-like and grow in fan-shaped clumps. Gardeners can choose from several thousand named varieties.
Bearded irises perform best in well-drained soils in full sun. To avoid problems in poorly drained soils, plant bearded irises in raised beds. They are excellent plants for perennial beds and borders. Bearded irises are hardy in USDA Hardiness Zones 3 to 10.
While bearded irises are widely grown, they are not trouble-free. Bearded irises quickly become overcrowded, resulting in fewer flowers. Clumps should be divided every 3 to 4 years. Several pests are problems on bearded irises. The most destructive pest is the iris borer. The iris borer larva tunnels into and devours much of the rhizome. Bacterial soft rot often attacks the borer-damaged rhizome turning it into foul-smelling mush. Various leaf spots can disfigure the foliage.
Siberian Iris
The beardless flowers of the Siberian iris (Iris sibirica) are smaller and more delicate than those of the bearded iris. They are available in shades of blue, purple, wine-red, pink, white and yellow. Siberian irises bloom in late May or June. The foliage of Siberian irises is narrow, upright and grass-like in appearance. The green foliage often turns to an attractive yellow or orange-brown in the fall. Varieties range in height from 12 to 40 inches.
Siberian irises perform best in moist, well-drained, fertile soils. They do well in partial shade to full sun. Siberian irises (USDA Hardiness Zones 3 to 9) are excellent plants for the perennial border and bog gardens. In comparison to bearded irises, Siberian irises have fewer insect and disease problems. Also, Siberian irises don't require frequent division. Plants should be divided when the centers of the clumps die.
Japanese Iris
The Japanese iris (Iris ensata) produces large, flat flowers that may be up to 10 inches across. The flower consists of three very large, nearly horizontal falls and three short, spreading standards. Flower colors include white, blue, purple, reddish purple and lavender-pink. The flowers are often marbled or speckled with a contrasting color. Japanese irises bloom in early to mid-summer (late June or July). The flowers are borne atop 30- to 36-inch-tall flower stalks. The leaves of the Japanese iris are dark green, sword-shaped and about 2 feet long.
Japanese irises require moist, organic-rich, acid soils. However, many garden soils in Iowa are alkaline. Gardeners with alkaline soils should incorporate Canadian sphagnum peat into the soil before planting. Canadian sphagnum peat will lower the soil pH and also adds organic matter. Japanese irises do well in partial shade to full sun. They are excellent plants for moist soils near streams and ponds.
Japanese irises, hardy in zones 4 to 9, don't have any serious pest problems. Plants can be left undisturbed for many years.
Crested Iris
A native of the eastern United States, crested iris (Iris cristata) produces 4- to 6-inch-long leaves from woody, spindle-shaped rhizomes. Flowers are pale blue to violet with white or yellow crests on their falls. Plants bloom in mid-spring. Crested iris performs best in well-drained soils in partial shade. It is hardy in zones 3 to 9. Because of its small size, crested iris can be grown in front of the perennial bed or border. It also can be naturalized in the woodland garden.
Yellow Flag
Yellow flag (Iris pseudacorus) has sword-shaped leaves and grows 3 to 4 feet tall. Plants bloom in late spring. The flowers are yellow with brown blotches on their falls. Yellow flag performs best in moist to wet soils in partial shade to full sun. It is an excellent plant for wet areas along streams and ponds. In spring, the newly emerged leaves of 'Variegata' have yellow stripes. However, this variegation disappears by mid-summer. Yellow flag is hardy in zones 4 to 9.
Sweet Iris
Sweet iris (Iris pallida) produces gray-green, sword-shaped leaves and fragrant, bearded, bluish purple flowers. The flowers appear in late spring. Sweet iris grows 2 to 3 feet tall. 'Variegata' has creamy yellow and green-striped foliage and pale blue flowers. The attractive, variegated foliage provides visual interest throughout the growing season. Sweet iris grows best in well-drained soils in full sun. It is hardy in zones 4 to 8.
Louisiana Iris
The Louisiana iris is the collective name for five species of iris indigenous to Louisiana and boggy coastal areas from Florida to Texas. They are valued for their colorful white, blue, red and yellow flowers.
The Louisiana irises grown in gardens today are hybrids of the native Louisiana irises. There are more than 500 varieties available. These hybrids vary in size, height, color and flower form. Some varieties have upright standards and flaring falls like bearded irises, while the flowers of others resemble Japanese irises. A few varieties have ruffled or lacy edges. Several have "double" flowers. Flower size varies from 4 to 7 inches. The bloom period is June or July.
While the Louisiana irises are native to the Gulf Coast states, they are remarkably hardy. They will grow in USDA Hardiness Zones 4 to 9. Louisiana irises prefer moist, neutral to acid soils in partial shade to full sun. Protected sites are best. During dry weather, water plants weekly. To help ensure winter survival, apply several inches of straw around the plants in November. Louisiana irises are excellent plants for water or bog gardens.
The colorful, orchid-like flowers of the bearded irises are indeed spectacular. However, don't forget some of the other attractive iris species when selecting perennials for the home landscape.
ml: isugarden
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