Answer: Iris need to be divided about every four or five years unless they become crowded sooner. Iris are generally divided in mid to late summer after they bloom, but it can be done any time during the spring or summer. Gently lift them and discard any soft rhizomes or sections with borer holes in them. Also discard the oldest sections, keeping the most healthy vigorous sections for replanting. Prepare the bed well, digging in ample amounts of compost or other organic matter because they prefer a rich soil. Also be sure it provides good drainage and is located in full sun. To replant, dig two parallel trenches and set the rhizome on the hill in between them, allowing the roots to trail down. Cover the roots and barely cover the rhizome with soil and then water well. Keep the plants weeded and be careful to clean up the iris bed thoroughly each fall. One helpful hint: you can label them by writing on the leaves with felt tip marker.
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