Bearded Irises:

Irises are among the earliest blooming and easiest perennials to grow. The most popular and widely grown iris is the tall bearded iris. "Bearded" refers to the presence of a furry strip on each of three drooping, petal-like sepals, called falls. The true petals are called standards and are upright. Flowers appear in late spring to early summer on stalks above the foliage. Flower colors vary greatly and are even available in two-color combinations. The leaves are stiff and strap-like and grow in fan-shaped clumps.

Bearded irises are available in a wide range of heights; miniature dwarf (up to 10 inches ), standard dwarf (10 to 15 inches), miniature tall (15 to 25 inches), intermediate (15-27 inches) and border (28 inches). Despite size differences, all bearded irises thrive in full sun and well-drained soil.

Culture:

Bearded irises grow from an underground stem known as a rhizome. Healthy rhizomes increase in size and develop branches or "off-shoots" which can be broken off (do not remove attached roots) and replanted. This method of propagation (division) should be done one to two months after bloom (usually July or August) every two to three years. When dividing, cut back leaves to one-third their length to keep newly planted divisions from being whipped by the wind and pulled from the soil. Otherwise, cut back foliage in fall as it begins to brown.

The planting procedure is the same whether planting a new plant or division. Cultivate the soil 12 to 18 inches deep and mix in composted organic material. Dig a hole about six inches deep and wide enough to accommodate the rhizome and its roots. Build a small mound of soil in the bottom and place the rhizome on it, spreading the roots carefully. Adjust the height of the mound so that the rhizome is just beneath the soil's surface. Fill in the hole and water. Bearded irises should be spaced 12 to 18 inches apart.

Irises require a well-balanced fertilizer such as 5-10-10 or 6-10-6, applied once in early spring and again in early summer following bloom. Ample moisture is required in spring when flower buds are developing and during flowering.

The Iris Borer:

The most serious iris pest is the iris borer, which overwinters in the egg stage attached to leaves. The eggs begin to hatch in late April, and the tiny caterpillars crawl up iris leaves and begin chewing and mining their way down within the leaf fold, eventually reaching the rhizome. Once in the rhizome, they continue to feed, sometimes reducing the rhizome to a hollow shell. Leaves which yellow and are easily detached indicate damage to the rhizome. The fully-grown borer crawls out of the rhizome and pupates in the soil in mid-August. The gray-brown moth emerges in mid-September to October, lays eggs on dry plant material and other garden debris and dies. Eggs overwinter until the following spring, when they hatch and the cycle repeats.

Eliminate iris borer eggs by removing and destroying debris in and around the iris planting in both spring and late fall, or by digging rhizomes and physically removing the borer, then replanting, in July or August.

Soft Rot:

Soft rot is a common problem of damaged iris rhizomes. Soft rot enters the rhizome through any wound, including feeding damage from iris borers. If soft rot is a problem, dig up the rhizome, scrape out the affected tissue, allow it to dry in the sun, then dip in a 10-12% solution of household bleach for a few minutes. Rinse with water and allow to dry before replanting.

Other Irises:

The beardless iris group includes those with smooth falls and leaves which are long (2 to 4 feet) and relatively narrow. Of this group, Japanese (Iris ensata), Siberian (Iris siberica and Iris sanguinea), and Louisiana (hybrids of Iris fulva, I. giganticaerulea and I. brevicaulis) are the easiest to grow in the Northeast. Japanese and Louisiana irises thrive in constantly moist soil or even standing water, while Siberian irises can tolerate moist conditions as well as those of a typical perennial border. They all prefer acidic soil and require regular fertilizations through the growing season. Unlike bearded irises, these should be transplanted in fall or early spring (divide in early spring) and require heavy watering during establishment. All but Louisiana irises should be planted in a sunny location where they can remain for several years. They do not thrive when disturbed too often. Borers do not as readily attack these irises.

The crested or evansia irises have a cockscomb-like crest along the lower half of the falls, instead of a beard. Iris tectorum, I. cristata and I. tenuis range in height from 6 to 12 inches, and bloom in May if provided with a moist, shaded location and soil rich in organic matter.

The bulbous irises include the so-called English, Dutch and Spanish irises, which have erect standards. Some have smooth bulbs while others have a netted or fibrous covering on the bulb. Bulbs are planted in fall. Iris reticulata and I. danfordiae bloom in late February or March. Still other lesser known irises--Iris pseudacorus, Iris laevigata, Iris virginica and Iris versicolor--do quite well submerged in a pond, at water's edge or in a moist part of the garden. Iris versicolor also does well in ordinary garden conditions.

Adapted from Leslie Dybiec, Ohio State University Extension, 2000