Irises have beautiful and colorful blooms that adorn gardens from spring until summer. They are hardy perennials that return each year with more plants than originally planted. While irises have a underground root structure similar to bulbs and are often called bulbs, they are in fact not "true" bulbs, they are actually rhizomes. No matter what you call them, iris bulbs (rhizomes) can be planted anytime you can work the soil; however, if you plant them in early spring, you may see some blooms in a few months.
Select an area that is in full sun to plant your irises. The more sun your irises get, the more they will bloom. The blooms will also be larger.
Amend your soil. Irises require soil that drains well. Till the top 12 inches of your soil with a garden rake. Mix in about three or four inches of organic matter, such as peat moss or compost. If your planting bed is a bit raised after this process, that will help with drainage.
Plant your irises just a half inch beneath the soil with the eye--or bud--facing up. Be sure to pack down the soil with your hands to remove any air pockets. Water well and after the water seeps in, pack down the soil once again.
Plant multiple irises about 12 to 15 inches apart. If you are planting in clumps rather than along a border, plant about four to six bulbs together (still 12 to 15 inches apart) to form one clump and then plant another clump of irises about four feet away. This will help prevent overcrowding.
Water your irises from springtime until after the last flowers bloom. Water only enough to keep the soil moist, not saturated. After the last blooms die, do not water irises anymore. Before the winter, mulch several inches over the bulbs to keep them warm.