The tall, beautiful iris, named after the Greek goddess of the rainbow, is one of the oldest garden flowers. In spring, bearded irises unfurl their buds to reveal a kaleidoscope of color.
Irises are hardy, reliable, easy to grow, and are deer-resistant and drought-tolerant. They also attract butterflies, hummingbirds and make lovely cut flower bouquets. These perennials flourish where winter temperatures dip below freezing and allow the plant to go dormant before next year's growth.
There are some 200 to 300 species in the genus Iris. The most familiar irises are the tall bearded irises, named for the soft hairs along the center of the falls. Species are separated into two major groups, rhizomatous and bulbous. Rhizomes are rootlike structures growing horizontally underground that are used as food storage. The bearded iris falls into this group. Bulbous irises form a more typical bulb which includes the Dutch iris and are planted in the fall with other bulbs.
It's important to know which irises you are seeking to divide. Division differs slightly. This article applies to the bearded iris.
As irises mature, the rhizome produces more rhizomes. When bloom production slows, about every three to five years, it is necessary to divide by removing and replanting the small rhizomes.
Divide at the right time of year, after flowering, when irises become dormant during late summer, reducing the chance of bacterial soft rot. Avoid dividing during winter when irises are trying to survive on stored energy in their rhizomes.
Snip the leaf blades to about one third of their height. This reduces stress as it concentrates on new roots, not maintaining the leaves. Carefully remove the entire clump with a spade or garden fork. Divide the rhizomes by pulling them apart with your hands. The rhizome should easily break off at a joint. If a sharp knife is needed to separate the rhizome, dip the knife into 10% bleach and water solution after each cut.
A good rhizome should be about as thick as your thumb, have healthy roots and one or two leaf fans. Large, old rhizomes that have no leaf fans should be discarded. Inspect each rhizome for iris borer (a fat, white worm). If you find a borer, destroy the rhizome. Soft, smelly, or rotting rhizomes should also be destroyed. Do not place in the compost. When planting the rhizomes, dig a shallow hole approximately ten inches in diameter and four inches deep. Build up a small mound of soil in the center of the planting hole. Center the rhizome on the soil mound and spread out the roots on either side. Fill the hole with soil. The top surface of the rhizome should be just visible at the soil surface. It's a common mistake to plant irises too deep. Tamp the soil firmly to anchor the rhizomes.
Good air circulation is essential. For the best display, plant the rhizomes singly or in groups of three so the fan of leaves face the same direction. Space the plants 12 to 18 inches apart (closer for dwarf varieties, farther apart for taller varieties). Newly planted rhizomes should be watered thoroughly. Do not mulch. Mulching retains moisture and could cause the rhizomes to rot.
Bearded irises will thrive in most well-drained soils. The ideal pH for irises is 6.8 (slightly acidic) but irises are tolerant of less-than-perfect soils. Test your soil before making any correction.
It is important that the roots of newly planted irises be well established before the end of the growing season, four to six weeks before the first hard freeze or killing frost. New growth may be noticeable within two to three weeks and begins with a new center leaf in the fan.
Leaves carry on photosynthesis for next year's growth. Don't trim iris leaves until fall. Only snip brown tips and cut the flowering stalk to the ground at a slant to discourage rot. This will reduce the chance of overwintering pests.
Break off seedpods that form after the blooms have faded. Seed formation saps energy needed by the rhizomes, roots, and leaves. Keep your iris beds free of weeds and fallen leaves so the rhizomes may bask in the sun.
Don't be afraid to divide your rhizomes. Dividing will multiply your iris to give to friends or barter with gardening pals. Remember your supply is always growing.
