By volunteer Stephanie de Moll
Whether dwarf, intermediate, or tall, bearded or beardless, irises are one of the most recognizable flowers found in a garden. Their seemingly endless color variations offer something for nearly every gardener. The one exception to the vast color palette is a true or pure red. And while not disease free as is sometimes claimed, irises are easy to grow in Zones 3-9 and are generally deer resistant.
Selecting irises is truly a matter of personal taste. Some gardeners love the tall, slender bearded iris while others are drawn to the petite varieties. Many examples of bearded iris can be found throughout The Oregon Garden during spring and early summer, most notably in The Iris Garden. When shopping for irises the scrumptious selections can be tempting, but it’s better to not completely fill a bed. Bearded irises need room to breathe, and they multiply quickly. Since they usually require dividing every four years, the bed will naturally fill in time.
Irises are drought tolerant, so they can grow in almost any well-drained soil. Clay soil needs sand or humus added to improve drainage. Sandy soil should be amended with compost before planting. Because irises like a slightly acidic soil, fertilizer requirements will depend upon the soil pH which can be determined by testing.
When planting, bury the roots firmly. Soil should just cover the top of the rhizome. The irises will grow best when planted facing the same way so they don’t begin crowding each other too quickly. Bearded irises should be planted soon after purchase, usually during July, August, and September. Rhizomes should not be held over for another season. Newly planted bearded irises do best with long, deep watering rather than frequent shallow watering. Once established, water when soil is dry.
Overwatering will rot the rhizomes. Irises like lots of sun too, at least six hours a day. Full sun is best. Deadhead flowers as they fade. Once blooming is finished for the season, flower stems should be cut down to the base.
When the time comes to divide the plants, dig them up a month or two after blooming, typically July and August. Cut the foliage down to six inches. Separate the plants by cutting the newer parts of the rhizome from the old; the old part may be discarded. Newly separated rhizomes should be well watered during dry periods.
After the first hard frost of the season hits, spotted or yellowed foliage should be removed, and remaining foliage should be cut back. All debris should be disposed of in the trash. Rhizomes may be protected, especially during the first winter, by covering with an inch or two or sand or mulch. In early spring, old foliage should be removed along with any winter mulch, and the plants should be fertilized. Fertilizer should not directly touch the rhizomes.
Beardless irises require a bit of different handling. They should be planted in the fall or the early spring. Before planting, soak the rhizomes overnight in water. After that the roots should not be allowed to dry out when out of the ground. Like their bearded cousins, the beardless iris should have good drainage. Siberian irises prefer being planted someplace permanent where they can grow undisturbed. They should not be dug up and separated like the bearded iris. On the other hand, Louisiana irises are creepers and will need to be dug and separated every couple of years.
Reblooming come in both bearded and beardless. These irises can bloom two or even three times during a season but are not guaranteed to do so. They may only bloom once the first year they are planted. In any case, reblooming irises also require some special care. Fertilize rebloomers first in the spring then again after the first wave of blooms have finished. Sprinkle a low nitrogen fertilizer on the ground around the root zone but avoid the rhizomes which will burn. Watering often is more necessary than it is for regular irises. Keeping the soil moist prevents rebloomers from going dormant.
Rebloomers grow fast and may need to be divided every two to three years. When dividing reblooming irises, dig and remove the new rhizomes to replant. Leave the old part of the plant intact to bloom again since some varieties must be well established before they will rebloom. The clumps should be dug deeply to save as much root as possible, and loose leaves should be removed. Reblooming irises should not be cut back during the late summer, or they won’t rebloom.
Irises make beautiful companion plants to roses and peonies or planted en masse in a bed of their own. Dwarf irises grow well in borders or rock gardens and are typically the first irises to bloom each spring. A collection of dwarf, intermediate, and tall varieties will extend the blooming season. And because irises are both easy to grow and come in a dazzling array of colors, they make a great choice for those new to gardening.