Hundreds of species and cultivated varieties of iris plants (Iris spp.) exist, with a wide range of flower colors and petal arrangements. Some irises are low-growing, groundcover-like, with tiny flowers, while others are tall-growing, erect and with large, showy blooms. Irises are perennial plants that grow from fleshy rhizomes and tend to multiply readily. The most commonly-grown irises are either bearded or beardless, the bearded irises with thick "falls," or lower petals, that hang down from the bottom of the flowers.
Water your iris plants deeply and thoroughly once each week while they're actively growing when rainfall is less than 1 inch. When rainfall is adequate, no supplemental watering is needed.
Spread a 1-inch-thick layer of organic compost on the ground around the iris plants once each year in spring, keeping the compost off the fleshy rhizome roots.
Deadhead the irises to remove the faded flower blooms. Then, cut the flower stalks back to the base of the iris plant to help the plant direct its energy toward plant growth instead of producing seeds.
Cut off all the dead foliage from the iris plants in fall and trim back the healthy leaves to about 5 inches above the ground level. Spread a 3- to 4-inch-thick layer of mulch over the iris plants after the first hard freeze that's frozen the soil to protect the roots from heaving out of the ground during winter.
Divide your irises once every three to five years in late summer. Dig up and separate the irises, discarding any older iris plants that have only a few white roots and ensuring that each division has at least one leaf fan.