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Irises change colors over the years

by Joanne Skelly
Purple irises bloom north of Genoa.
Kurt HIldebrand

I am fascinated with German bearded irises with their frills, color combinations and scent. I’m also interested in the changes that occur to the flowers after a number of years. I have had deep goldenrod ruffled irises lose their ruffles and fade to a lovely light yellow after years in the same location. Some have even turned white. My pale blue irises now look more pale lavender. This color change seems to prevail only in the fancy irises, not in the old-fashioned ones and may be a result of aged clumps.

There are more than 250 species of irises with new ones coming out yearly. The bearded hybrids that grow from rhizomes are the most common. The rhizomatous irises include not only the German bearded, but also dwarf, beardless hybrids and Japanese irises. However, bulbous irises are also available and include the Dutch, Spanish and English irises. Bulbous irises are always beardless.

My friend Peggy recently gave me some beautiful Dutch iris cut flowers in blues and yellows. These delicate-looking colorful blooms grow on slender stems with much smaller leaves than those of the German bearded irises. These are generally the irises sold by florists. The bulbs are planted in the fall, just like daffodils or tulips. And, just like daffs and tulips, the foliage dies back after blooming, something the German bearded foliage does not do. The bulbs can be left in the ground year after year if the soil is kept on the drier side.

When irises get overcrowded after three to four years, they need to be divided or the blooms will decrease, look less than stellar, and, perhaps, lose their original color as mine did. I usually divide irises in the late summer to late fall when the temperatures decrease. Irises require good drainage with more water in the spring and during bloom than in the after-bloom stage. Water regularly for six weeks after blooming. Then, reduce watering a bit for the rest of the summer. Buds for next year’s flowers form after this year’s bloom cycle is over. Fertilize with a nitrogen fertilizer, not only in the spring prior to bloom, but also after blooming.

The German bearded flowers do not last long. Each day I remove the spent flowers from the day before, finally cutting the spent flower stalk off down low. However, the blade-like leaves add almost yearlong interest to a perennial bed with their silvery blue color and shape.

JoAnne Skelly is Associate Professor & Extension Educator, Emerita, University of Nevada Cooperative Extension. She can be reached at skellyj@unce.unr.edu.