Irresistible, Iridescent, Iris

by Joyce Schillen (copyright 2004)

Henry Wadsworth Longfellow described the Iris as “fair among the fairest," and many gardeners would agree. They consider it to be among the easiest of perennials to grow, as well as one of the most beautiful. Iris can provide a rainbow of color in your garden from early spring into summer with minimal effort on your part.

In fact, the iris was named for the Greek goddess of the rainbow, a testament to the wide range of colors that are available. Solid and two-toned varieties bloom in just about every color except true red.

Irises have smooth, sword-like leaves that grow from a few inches tall to as tall as four feet. The upward-reaching petals are called the “standards” and the downward-drooping petals are called, likely enough, the “falls”.

The most commonly grown variety is the familiar bearded iris, which gets its name from the hairy strip resembling a woolly caterpillar that decorates the center of each “fall”. Also grown are the crested iris, a diminutive American wildflower, and Japanese and Siberian iris which are clump-forming with grass-like leaves. Two special varieties are Pacific Coast Iris, a drought-tolerant native that requires acid soil, and Water Flag Iris, a water lover, which makes a nice choice for wet spots.

With such a wide variety of colors and types, there’s an iris for every situation, including borders, beds, rock gardens, edgings, ground covers, ponds, and even in containers. Iris make striking cut flowers, as well as looking lovely in the garden.

By planting a combination of early-, mid-, and late-season bloomers, a spectacular iris show is possible from February into June. A few varieties are called “continuous bloomers," but that just means they bloom longer than others. The class of iris called re-bloomers, which bloom again in the fall, usually do not perform well in hot summers.

To get your collection started, make friends with someone who already grows iris in your neighborhood. Most gardeners are begging for someone to take over the orphans when it comes time to divide mature plantings.

Cultural requirements

• Grow iris in full sun, except for crested iris which likes light shade. All varieties will tolerate light shade but won’t bloom as well. Planting under a tree canopy is okay if leaves don’t shade the plants when they bloom in spring.

• Well-drained soil is a must, especially in winter. Iris tolerates a wide range of soil types, from sandy loam to clay, as long as the soil drains well. Till decomposed leaves or other organic material into the soil before planting to improve drainage. Most iris prefer a neutral pH

• Prepare a deep bed. Rhizomes creep along the surface, but iris also sends roots deep. Before planting, work in bonemeal or another high-phosphorus fertilizer.

• Plant rhizomes just barely under the soil surface with leaves emerging into the sunlight. Space plants 1 to 2 1/2 feet apart, depending on height.

• Iris needs abundant water just before and during blooming, but bearded Iris is quite drought resistant the rest of the year. When establishing new plants give them 1” each week. Japanese, Siberian, and crested Iris prefer moister soils than the bearded types. To increase rhizomes, water once a week for six weeks after blooming is done.

• Fertilize established plants with an all-purpose, balanced fertilizer in early spring when growth begins, and again at half-strength after blooming finishes.

• Remove fading blossoms and seed pods; clean up withered foliage in fall to prevent disease and insect build-up.

• Divide iris every three or four years, or when plants become crowded. Divide in spring after the plants finish blooming, or later on in early fall. Dig up clumps and wash them with a hose. Slice into sections with a clean, sharp knife. Discard portions that are old or show signs of disease. Let rhizomes dry off in the sun for a few hours before replanting. In fall, trim back the foliage for easier handling. Don’t cut leaves back severely just after flowering because plants need their leaves to store up energy for next year. In fall, cut back by two thirds.

• Iris is relatively trouble-free to grow. The most common iris pest is the iris borer, which tunnels the lower portion of leaves. Keep an eye out and squash any larvae found in the tunnels. Spread pyrethrum dust around the base of plants in spring to kill the hatching larvae that emerge from the soil to climb the foliage. Various fungi can cause leaf spot or rust on leaves and other problems. It’s best controlled by preventing the over-crowding of plants.