When to plant
Plant the rhizomes soon after you receive them. Remaining out of the ground, stored in a dry indoor environment for several days, will not be harmful, but planting within a week or two is best.
Like many perennial plants, iris may be moved at any time if proper care is taken. However, the best time to move them is during the period which extends from soon after they bloom until the time when new growth develops. If you move your iris within this period, you will have the least trouble and the greatest success.
Where to plant
Generally, bearded irises thrive in USDA Hardiness Zones 3 through 10 in the dry-summer parts of the West and in 3 through 8 in the rainy-summer East. Where they are hardy, bearded iris are stalwarts of the perennial border. Even in old, neglected gardens you'll find iris still blooming. They prefer at least 6 hours of full sun, deeply cultivated, rich soil with a pH near neutral (6.5 to 7.0)
A well-drained, sunny location is best. Bearded irises prefer a full day of sun, but they will grow and bloom well if given at least half a day of sunlight. The bearded iris will not tolerate "wet feet". Gardeners can avoid many problems by providing good drainage to protect the iris from getting "wet feet." Iris will grow in any good garden soil. If other plants grow well in your garden, iris will flourish in it.
Most local soils are fine for irises as they are, if there is good drainage. If a soil test shows nutrients to be lacking, add them as indicated. If a fertilizer is needed at planting, use bone-meal or super phosphate fertilizer.
How to plant
Soak the rhizomes and roots in water a couple of hours immediately prior to planting. Dig a hole six inches deep and build a mound inside the hole. Place the rhizome on top of the mound so that its top will end up even with the soil level and its roots are spread out over the mound. Fill in the soil and firm it down. In a good loamy soil, the rhizome should be just barely covered. In a heavy clay soil, the top of the rhizome should be showing above the surface. Never plant too deep. Water well immediately after planting. Thereafter, water only in extended dry periods—bearded irises are native to near-desert conditions. Manure or compost should not be piled around the rhizome. Do not mulch—using Preen helps to control weeds.
Bearded irises in general are light feeders. Each spring, after growth begins, one handful of 5-10-10 or similar formulation can be sprinkled in a circle around each clump. It is good to make these applications just before a rain, or to hose the plants clean of any fertilizer which has fallen on the new growth. Some gardeners like also to provide a light feeding of Miracle-Gro or equivalent about a month before bloom time. If the bearded iris is a reblooming variety that you wish to encourage to do so, make sure it continues to be regularly watered after spring bloom time, and provide it with an additional feeding at that point as well.
Cut them back?
Healthy green leaves should not be cut back. As old leaves naturally wither and brown, remove them. Also remove any diseased foliage. Be especially careful to remove and destroy all old leaves and other debris late in the winter, before March, when warm days could hatch the eggs of insects that overwintered on them.
Blooming stalks can be enjoyed in the garden or cut for display indoors in a vase or arrangements. Spent flowers should be snapped off. When the stalk has finished blooming, snap it off close to the ground by bending it on a dry day.
Although your bloom should be fairly good the year after transplanting, your best bloom will occur in the second to fourth years, so do not divide your clumps too soon. But after three or four years the rhizomes will become crowded and should be dug, divided by using a knife, and replanted. This is also the time to revitalize your soil by adding humus and fertilizer as was recommended for the new planting.
Dig the entire clump during a period when your iris is not blooming. Spring blooming iris divide it in fall, fall blooming iris divide it in spring. If it blooms in summer divide in either spring or fall. Cut the leaves back to 6” or so. Remove the soil and separate the rhizomes. Discard old rhizomes, keeping only those with fans attached and their increase—the new plant buds just emerging from them. Wash them off, dry them, and trim the roots to 4” or so. Label them, and store them in a cool dry place, to replant soon