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Few plants come in a wider range of colors than the
iris. More than 300 species have been identified worldwide, and many of
them are long-lived perennials that flourish in central-Illinois gardens. In the past 50 years, thousands of cultivars, in
various colors, sizes (ranging from the 6-inch dwarf crested iris to the
5-foot-tall yellow flag iris), and forms, have been developed. I have
approximately 20 cultivars of bearded iris in my garden, including a small
white-and-lavender one that has been passed down through four generations
of my family. The upward-reaching true petals of an iris are called
“standards.” The turned-down petals are referred to as
“falls.” Many cultivars have different-colored standards and
falls. The most common species of iris is bearded German
iris, Iris germanica. This species grows 18 to 36 inches tall and blooms between late
spring and midsummer, depending on the cultivar. Plants grow best in
well-drained soil in a full-sun location; they will not tolerate poorly
drained soil. Flowers come in a rainbow of colors, include pink, varying
degrees of purple, pale and bright yellow, peach, pale green, light blue,
white, tan, bronze, almost black, and bicolor. The dwarf crested iris, Iris
cristata, is a native low-growing,
rapidly spreading plant. The flowers, which appear in early spring, range
from pale blue to lilac to lavender, with gold crests on the falls. These
plants perform best in part shade but will tolerate both full sun and full
shade. The Siberian iris, Iris
sibirica, grows 2 to 4 feet tall. It has
graceful blue-green arching grasslike leaves, which are a nice feature in
the garden all summer, and flowers of blue, purple, maroon, white, pink, or
yellow. The Siberian iris tolerates a wide range of soil-moisture
conditions, from average to wet areas, but will not tolerate standing
water. The plant flowers best in full sun but will also bloom in part
shade. The Siberian iris differs from the bearded iris in that it is easier
to grow and has fibrous roots rather than rhizomes. It has no serious pest
or disease problems and is less susceptible than other irises to iris
borers and soft rot. “Caesar’s Brother” is a 3-foot-tall
cultivar with a deep-purple flower. The Japanese iris, Iris
ensata, has large showy, frilly, flat flowers.
It thrives best in acidic soil and flourishes in wet environments, even
shallow water. The Japanese iris needs ample organic matter for nutrients
and prefers at least six hours of full sun each day. Bearded irises are susceptible to a few problems,
both animal- and microbe-induced. Imagine my disappointment last weekend
when I noticed that several of my iris plants were looking rather frail.
Closer inspection revealed that the rhizomes had turned to mush as a result
of bacterial soft rot. In addition to bacterial soft rot and other
bacterial infections, irises are vulnerable to fungal infections, leaf
spots, and infestation with iris borers. These destructive caterpillars are
difficult to control and a menace to all types of irises; see the
University of Minnesota Extension Service’s “Yard and Garden
Brief,”
www.extension.umn.edu/yardandgarden/ygbriefs/e122irisborer.html. Proper
sanitation is important; remove and discard infected rhizomes and plant
parts. To help keep a healthy iris healthy, be sure to remove old blooms
after flowering.
Most iris clumps become crowded and should be divided
every three or four years. Crowded plants will produce fewer flowers. Be
sure to place iris rhizomes at ground level rather than burying them in the
soil; iris plants need good air circulation to help prevent disease. Consider adding a combination of irises to your
perennial garden. Learn more about various species and cultivars at the
Missouri Botanical Garden’s “Plant Finder” Web page,
www.mobot.org/gardeninghelp/plantfinder/serviceplantfinder.shtml.
Jennifer Fishburn is a horticulture educator with the
University of Illinois Extension Sangamon-Menard Unit. Contact her at
www.extension.uiuc.edu/Sangamon.
This article appears in May 10-16, 2007.
