Spring is the best time to divide Siberian iris in the cold climate of the Northeast. August is the second best time to divide and plant. This timing gives the plant a chance to establish a strong root system before winter arrives.

If these plants become crowded, vigor declines and blooms get smaller over the years. So diminishing bloom size is a sign that it's time to divide and transplant. Two to four fan divisions are recommended when dividing. Keep roots moist while plants are out of the ground. Plant rhizomes 1 inch deep (slightly deeper in sandy soils).  

Keep newly transplanted plants well watered at all times, approximately 1 inch per week, and mulch for their first winter. Enjoy the flowers of your labor the next growing season!

For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service