Now is the time to rejuvenate iris

Happy Gardening
by William H. Bohl

Drive a vehicle and you’ll eventually have to replace the tires. Own a house and someday the roof will need repair. And, who hasn’t had to replace a water heater? Tires, roofs and appliances don’t last forever. We all know that. However, too often people plant perennial plants in their landscape thinking they should last forever and require little to no care. Not so.

Keep in mind that in the plant world, perennial doesn’t mean forever. It just means a plant species generally lives three or more years. However, some perennial species, such as trees, may live for decades. Furthermore, many perennial plants grown in landscapes need intermediate care so they’ll be more productive and/or attractive. One such plant is iris. Likely the most popular iris in our area is the bearded iris, so called because of a row of hair (fuzz) found on the petal that grows downward.

Irises are a long-lived perennial that produce a wide array of flower colors with over 200 species and thousands of cultivars (varieties). Irises provide a landscape with spring color that lasts several weeks. Irises do best planted where they receive full sun with good soil drainage. Soil that remains wet is very detrimental to iris causing a greater chance for the rhizome to rot. The rhizomes of irises are thick underground stems that produce the leaves and from which the roots grow.

Rhizomes will branch as they grow, and over time will begin crowding each other. To keep irises healthy and producing flowers, it’s necessary to divide the plants (rhizomes) approximately every three to five years. Dividing and replanting should be done in July to early August, so there’s still time this summer to do this.

Dig the rhizomes out of their current location and divide the rhizomes discarding the smaller, less healthy ones. Cut the leaves in a point to a length of about six to nine inches. Space each rhizome about 12 to 15 inches apart with leaves facing the same way. Dig two parallel shallow trenches and place the rhizome on top of the ridge between the trenches, and place the roots in the trench on either side of the ridge. Replace soil so that it’s level and is covering the rhizome with no more than one-half inch of soil, and then water thoroughly. A minimal amount of water will need to be applied after transplanting as applying too much water is detrimental.

Happy Gardening!

Bohl is Extension Educator with University of Idaho located in Blackfoot. He may be contacted at 785-8060 or

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