Irises (Iris spp.) thrive in full sun to partial shade in fertile, well-drained soils. These hardy perennials grow in U.S. Department of Agriculture plant hardiness zones 3 through 9, depending on the species and bloom in early to midsummer. With proper care and enough fertilizer, irises produce an abundance of blooms on slender stalks held above fanlike foliage. Colors range from traditional blue, violet and yellow to vibrant shades of pink, red, orange and green. For the biggest and brightest blooms irises need to be lifted and dividing every three to four years, when you can give them an extra boost with bone meal.
Till the soil to a depth of 8 to 10 inches to create a new iris bed in the summer after dividing your irises, or in late summer or early fall if you bought new iris rhizomes
Dig 5- to 6-inch-deep holes, spaced 12 inches apart. Apply 1 cup of bone meal per 1 square foot to the soil in the bottom of the planting holes and mix it into the soil. Cover with 3 to 4 inches of soil.
Place your iris rhizomes so the roots on the bottom spread out over the soil and the top of the rhizome sits at or slightly below the soil. Place the rhizomes to sit slightly above the soil level if you have heavy soil.
Firm the soil around the iris rhizome with your hands.
Water thoroughly to moisten the soil to a depth of 6 inches. Water once or twice a week to keep the soil moist as the new roots become established.