Robin Sweetser Nance Trueworthy

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The genus Iridaceae includes more than 200 species, all originating in the northern hemisphere. Some irises need arid conditions to thrive while others grow in standing water or streamside. Some grow in the shade while others require full sun. They range in size from a few inches tall to over four feet. There is sure to be a type of iris that will be perfect for your situation.

Bearded Iris
The hardiest bearded irises found in the wild were used to create our modern hybrids, making them among the easiest irises to grow. The dramatic blossoms have three upright petals in the center called standards and three sepals on the outside called falls which can either flare out to the side or droop down. In the center of each fall is the beard, a strip of fuzzy hairs which guides pollinating insects inside the flower. Barbara Schmieder, President of the Iris Society of Massachusetts, has been hybridizing bearded iris with her husband David for over ten years. “I find bearded iris most exciting because of the great variation of color,” she says, and they do come in every color and combination of colors in the rainbow except true red. Flower forms vary too, with laced, ruffled, or smooth petals. The waxy, gray-green, sword-like leaves overlap at the base like a fan. Even when the plants are not in bloom, the foliage lends interesting structure to the garden. The American Iris Society divides bearded irises into six groups by size and flower. “If you have some of each type of bearded iris,” says Barbara, “you can extend the bloom time and have irises blossoming in your garden from the end of April until mid-June.”

Growing a Beard
All bearded iris arise from a swollen stem called a rhizome that grows horizontally at the soil surface. Smaller white roots grow down from the rhizome anchoring it to the ground. If the rhizomes are not divided periodically they will form a dense mat and flowering will be reduced. Here in New England, July and August are the best times to divide and replant bearded iris. Dig rhizomes up and snap or cut off the old parts since they will not flower again. Choose a location with at least six hours of direct sunlight, good drainage, and soil of neutral pH (6.5-7.5). Add lime if acidic and amend the soil with lots of compost. Next season’s plant emerges from the fan end so when replanting, face it in the direction you want plant growth to travel. Space rhizomes 1–2 feet apart for tall types, closer for dwarf ones. Since bearded irises grow with the top of the rhizome above the soil, dig a shallow hole or trench, and make a mound of soil in the middle to place the rhizome on, spread the roots out over the mound and cover the roots, leaving the tops of the rhizomes exposed. Water well to settle the soil around the roots and continue to water sparingly once a week until new growth begins. Once established, bearded irises are drought- tolerant and won’t need additional watering. Barbara advises fertilizing early in spring and right after blooming with compost or a low nitrogen organic fertilizer. She also recommends using alfalfa meal as a side dressing.    

Japanese Irises
The blossoms of Japanese iris differ from those of bearded iris because they have small standards and wide falls, giving the blossom a flatter appearance. The exotic flowers are enormous, reaching 8–12" across, and are held high above the leaves, looking like a colorful butterfly caught in mid-flight. Sharon Whitney of Eartheart Gardens in Harpswell, Maine describes them as being more feminine and graceful than bearded irises. The blossoms, which can be singles with three falls or doubles with six, come in a wide array of colors with marbled, dusted, edged, and speckled effects. Instead of a fuzzy beard they have a pale yellow spot called a signal at the base of each fall. They bloom much later than tall bearded irises, extending the iris season into early August. Japanese irises need a moist site, rich in organic matter. Their ideal location is at water’s edge where the roots can spread into wet, acidic soil but Sharon says they do not like to have their roots standing in water during winter. She also cautions us that lime is fatal to these acid-loving plants. Japanese irises grow from a finger-shaped, fiber-covered rhizome which grows in a more upright position than the creeping bearded iris rhizome. Plant the rhizome with the crown of the plant (where the leaves and rhizome meet) 2"–3" deep. They can be divided after flowering but never let the rhizomes dry out. Water daily for a few weeks, and then give two inches of water a week until they are established. “Japanese irises are heavy feeders,” says Sharon.“Feed them in early spring and again right after blooming with a balanced fertilizer like 10-10-10 or Holly-tone.”

Siberian Irises
Siberian irises are also beardless but bear many small, delicate-looking flowers on branching stalks. Their 30" tall foliage is thin and graceful, more of a rapier compared to the broadsword leaves of the bearded iris. The flowers are mostly blues and purples, white, and a few yellows. Their center-style arms, which are almost hidden on a bearded iris, are also decorative. The petals can have ruffled edges and most have contrasting signal patches of white or yellow. Hybridizers like Marty Schafer of Joe Pye Weed’s Garden in Carlisle, Massachusetts, are constantly selecting seedlings that have strong growth, lots of buds, and interesting color variations. Siberians bloom a little later than tall bearded irises. Instead of growing from a fat rhizome, Siberians arise from thinner, finger-sized rhizomes that need to be completely buried when planting. They don’t need to be divided as often as other irises but when a mature clump begins to die out in the center, it is time to dig it up, divide, and replant the vigorous pieces. They will flower more abundantly in full sun but can tolerate some shade. Siberians need more water than bearded types but once they are established, Marty says they can take pretty dry conditions. These irises are the toughest of all and have little pest or disease problems.

For more information on irises contact the American Iris Society at irises.org.

Dr. Currier McEwen of Harpswell, Maine, was one of the foremost hybridizers of Japanese and Siberian irises in the world. Considered the father of the modern Siberian iris, he developed the first colorfast yellow. Even though he passed away in 2003, his floral legacy lives on. Sharon Whitney, who worked with Dr. McEwen for over twenty years, continues to grow and sell his introductions at Eartheart Nursery in Harpswell.