The best time is late fall. However you might try some now (as soon as possible) and save a few others for this coming fall. However, now (late winter) is not a bad time to transplant them.
Dig the irises and cut off the end 4 inches of each runner. Set these sections about an inch deep in soil that has had a couple of inches of compost mixed into it. Choose a sunny location. Some late afternoon shade is all right. Mulch the area a couple of inches deep after planting.
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