HORTICULTURE ARTICLE - AUG 2006

In mythology, Iris was the goddess of the rainbow and in the classic story “The Iliad’, she was a messenger from earth to the gods. Irises are also messengers of perfume and color to modern gardeners. Most people recognize the members of this plant family with their sword-like fan of leaves and distinctive bloom of three petals upright (standards) and three petals downward (falls). For gardeners, the family is usually divided into irises grown from rhizomes and those grown from bulbs. The bearded irises of the garden grow from a hortizontal fleshy stem called a rhizome. Also grown from rhizomes are the beardless irises and the crested irises. The bulbous branch of the family will be discussed at a later time but it includes irises from the Juno, the Reticulata and the Xiphium groups.

The beard or brush-like growth on the lower three petals (falls) of the flower easily identifies the bearded irises. These species are said to have originated in the Middle East and Mediterranean areas. These irises prefer good drainage and their rhizomes planted horizontally with the top of rhizome exposed. For judging iris shows and predicting bloom times and size, there are six divisions of bearded iris. These include miniature dwarfs (MD) which are 8” or less and earliest to bloom in spring. They do well in raised beds and rock gardens if heavy clay soil is a problem The next group to bloom are the standard dwarf bearded (SDB) which are also early, unfolding a burst of color. They are usually in the 8” to 1” height range. If bearded irises are taller than 16”, they are called intermediates (IB). The last three groups are the smaller, dainty flowered plants called tall bearded iris varieties. They are divided into border bearded (BB), miniature tall bearded (MTB) and regular tall bearded (RTB). These plants have ruffled or lacey smaller flowers on wiry stems and are often referred to as “Butterfly” or “table iris”. In addition to thousands of color combinations of falls, standards and beards, some bearded irises are referred to as remontant meaning they may bloom again in late summer of fall if fed and watered well. One variety of this type is I. ‘Immortality’ which is pure white and does well in central Illinois.

Beardless iris include the Spuria (2’-5’), Siberian, Japanese, Louisiana, Pacific Coast Natives and the species irises. Spuria blooms suggest orchids with stately foliage and bloom in whites, yellows, blues, wine or brown. Siberian irises delight in cold and wet areas. Their blue, violet and/or white flowers usually have large falls and smaller standards and grow in the height of 2-4’. Japanese irises are beardless and have spectacular flowers with huge, flattened forms, ruffled and veined with white. They prefer slightly acid soil and have been hybridized for hundreds of years.

Louisiana irises hail from the Gulf Coast and love acid wet soil to produce wide petals with open blooms and many are hardy in Illinois. Pacific coast Natives (PCN) grow primarily on the western coast regions and are not happy in Illinois. Of the species irises, there is I. confusa (Evansia) which grow in frost-free areas and I . Missouriensis requiring wet spring and cool summers. Another class of iris grown from rhizomes is the Arils iris which include two very different irises, the oncocyclus and regalia irises from the Near East. They have sparse beards, much veining and amazing colors. They really grow successfully in the hottest and driest region of the U.S. southwest. They often are used in cross breeding programs with the more common bearded varieties. The final group is the Crested iris which are known as Evansia iris. Their flowers are flat and have a crest or ridge on each fall instead of a beard.

THERE'S STILL TIME TO DIVIDE AND PLANT. Most irises are best divided and planted in midsummer to autumn. Irises with rhizomes need to be planted carefully and not too deep. Place rhizomes with the leaf fans facing outward if in a cluster so they will grow outward to minimize crowding. Division usually is recommended every three to four years. If you must, feed them with low nitrogen fertilizer and take care to not mulch rhizomes to deter root rot. Major cultural problems are planting bearded varieties too deep which causes bacterial root rot. The major pest is the iris borer but thrips and aphids can be a nuisance. Keeping the growing area free of weeds and old foliage and locating plants in full sun in soil with good drainage are the best ways to avoid trouble. If borers are evident with streaks or disfigured foliage or if rhizomes are disfigured or soft, dig and destroy affected rhizomes immediately and replant any healthy parts in a different location.