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Wednesday, May 16, 2007 10:00 pm

An eye for iris

Thousands of cultivars provide range of color to accent any garden

art4094
A common iris
PHOTO BY FRED BLOCHER/MCT
Untitled Document 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. 
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