What is the best time of year to plant iris bulbs?

For spring to early summer blooms the following year, iris bulbs should be planted from mid-summer to early fall in U.S. Department of Agriculture plant hardiness zones 4 through 9. This lengthy head start gives iris bulbs the chance to feed and develop their blooms.

The Arizona Cooperative Extension recommends storing iris bulbs in vermiculite or peat moss in a cool, dry location until planting time. Irises planted in locations with nutrient-rich, well-draining soil and at least six to eight hours of sunlight thrive for many years. After two to five years of established growth, iris rhizome clumps should be divided shortly after they finish blooming. Separated rhizomes should be planted in new locations to maintain healthy, productive plants.