Iris is a stalwart of the spring perennial garden, with color and texture that is second to none.

However, iris can be "finicky" and in need of yearly attention to keep them at their peak.

These plants grow in clumps from bulbs, rhizomes or a massive root system. Each type is different—bearded iris is more rhizomatous while Dutch iris is from bulbs. Japanese and Siberian iris are more "root system" oriented.

Yet, iris also share a similar characteristic. Once the iris produces a fan of leaves and a bloom, that fan hardly ever produces another bloom.

"In order to maximize flower production, iris need to be lifted and divided at least every three to five years to ensure maximum blooms," explains David Robson, University of Illinois Extension horticulture educator.

Plants are divided during the hot part of August, usually between the middle and end of the month. Dividing and replanting by September 1 helps guarantee establishment of the planting before winter.

"The later the division, the more likely plants will suffer winter drying," says Robson. "Flower production the following year also decreases with later transplanting."

Clumps should be dug and most of the soil washed away from the root system or rhizome. Carefully inspect clumps for diseased or insect-damaged roots/rhizomes. Remove those pieces and compost them.

Clumps can be divided with a sharp knife. Make sure each section contains a fan, a 2- to 3-inch piece of rhizome for bearded iris, and a strong root system.

"The best bets are the new fans produced this spring and summer," says Robson. "Old fans will not bloom again, but they will produce additional fans in following years. If you use old fans, you will have to wait an additional year before seeing flowers."

Set iris rhizomes an inch below the ground and firm the soil. Water thoroughly. By next spring, the soil will have settled around the plant, and the rhizome should be at ground level.

Cut the fans back by half with a pair of scissors to limit wilting. Fans still may fall over due to the transplanting.

Japanese and Siberian clumps should be divided with a sharp knife or shovel. It is difficult to distinguish old fans from those produced this year. Therefore, there is little need to separate out the old fans. Make sure there are at least two fans per Japanese or Siberian iris planting. Bulbous iris can be separated and replanted in September or October with other spring-flowering bulbs.

Make sure plants receive adequate moisture throughout the fall to avoid winter injury.