Irises are perennials, meaning that they bloom year after year from the same set of bulbs, if conditions are right. They come in a range of colors and styles but always have the same blooming structure: three petals rising up behind the center of the flower, with one hanging down in front. For irises to bloom at all, the rhizomes must find the right care.
Irises bloom from rhizomes, or bulbs, which hold all the plant's necessary growth materials. Healthy rhizomes are slightly moist and firm, without any signs of rot or damage. In many cases, a rhizome comes with clippings of shoots and roots already attached.
The best time to plant iris rhizomes is in late summer, before the first frost but after the blooming period. This gives the rhizomes time to establish and take root for spring growth. Late summer to fall is also the best time to divide and transplant irises.
For rhizomes to succeed in growing irises, they must grow in the right location. Put rhizomes in a spot where they'll get full sun for six to eight hours a day, or only partial shade, for successful growing and blooming.
Irises require quick-draining and loose, fertile soil. Gardeners should mix compost, quick-draining soil and fertilizer into the top 10 inches of soil a week before planting, to give rhizomes the best chance at thriving growth.
Iris plants that bloom and pollinate produce large seedpods at the end of the blooming period. The seedpods sit at the center of the pollinated flowers, and hold seeds that develop into rhizomes, given time and care. Cut off seed pods, separate seeds and plant them in individual pots, using quick-draining soil. Seeds require full sun and an inch of water a week, and develop into rhizomes within a couple of months as they sprout. Maintain irises in pots until they have solid rhizomes at their roots, as rhizomes are stronger and transplant more successfully to the garden in spring or fall.
According to Iris Colorado, irises are some of the easiest and most beautiful perennials to grow. This is partially because of their easy division, which is also accomplished through the rhizomes. Gardeners dig up the rhizomes of established plants, divide them, and move some of them to new locations to propagate new plants.