Iris are truly plant-them-and-forget-them perennials that will almost grow themselves. Once they're planted in a sunny, well-drained spot, leave them alone and let them work their magic. However, a few minutes of extra care at the end of the growing season will ensure that the iris will happily present you with colorful blooms for many more years.
Cut off the iris blooms with clean scissors when they fade. Cut the bloom and the stem clear to the ground, but don't remove any of the foliage while it's still green. The iris rhizomes need the energy from the foliage to grow throughout the winter and bloom the following spring.
Remove the foliage when it dies down and turns yellow. Keep the planting area tidy, and remove any weeds and debris. Iris prefer dry conditions, so remember to water only during very hot, dry periods.
Cover the iris plants with a 2- to 3-inch layer or organic mulch if you live in a climate where the temperatures often fall below freezing. Straw, leaves, bark chips or pine needles are all good insulators. Remove the mulch early in the spring so the iris can grow freely.
Divide the iris if they've been in place for more than four years, or if the plants are crowded. Dig the iris rhizomes with a garden fork. Wipe a sharp knife with rubbing alcohol and cut off rhizomes that have no buds or leaves. Cut off brown spots, and dispose of the old, dead sections in the middle of the clumps. Soak the divided rhizomes in water until you're ready to replant them.