Gardening Topic for May 2004
The Iris Family

Provided by the Western Massachusetts Master Gardener Association
www.wmassmastergardeners.org.

Settled just six months in my new home in the spring of 1998 I watched with great excitement a patch of iris grow and bloom in the garden.  They were regally tall and straight. The vibrant color seemed more real of an artist’s paint palette than a plant in my garden. Its fragrance stirred my spirit. I fell in love. That same week, friends called from New Hampshire, saying they would like to pick me up and take me to an iris flower show near my home. The message was clear. My new life in my new home had arrived. That day in Shelburne Falls, the ongoing message of new life continued to unfold for me. I met other irises and other iris lovers at the annual Western New England Iris Association’s show. With great excitement, I gratefully paid my three dollars dues and began my new journey.

             Growing iris has introduced me to new people, opened new opportunities to teach and share and to live life in my garden, cherishing life everyday in all new ways. Over these last six years I learned that with knowledge and planning, iris of different species will bloom in my gardens from late April until late July.  The tiny bulbs of the
I. reticulata blooms along with the crocuses, than the bearded iris follow in May and June with the Siberians joining in June and the Japanese filling in the end of the season during July.  I learned I can cross (hybridize) some of these species, and grow a new hybrid and name it myself. If the American Iris Society judges it worthy, it could be awarded the Dykes Medal along with other prestigious awards. Also, I have learned how to identify and manage pests and disease common to iris, particularly the dreaded iris borer.

A close examination of the flower head provides the first clues to its species. Is it a bearded iris or a beardless? In the bearded family, an array of species include the earliest blooming iris ‘Miniature dwarf bearded’, then follows the ‘Standard dwarf bearded’, than the ‘Intermediate bearded’, followed by the’ Border bearded’, next the ‘Miniature tall bearded’ and of course the most familiar species of all the ‘Tall bearded’. Along with the Tall bearded iris, the beardless Siberian iris begins blooming and is probably the other widely known irises. The season ends with the other beardless iris the Japanese iris.

The Siberian irises are identified as sub series Siberica and Chrysographes.  I. siberica and I sanguinea are Sibericas and have long been standing staples in herbaceous garden borders. A third siberica species, Iris typhifolia is a newer and less known and available. The second subseries, Chrysographes also known as Sino-Siberians, contains at least eight species. They are more demanding in their requirements and are not widely available. The green foliage of the siberian iris arches gracefully and the flowers are smaller and more abundant. Its impact in a garden is great. Their colors, for the most part, are shades of purple, blue and white unlike the bearded. Iris ensata, known widely as Japanese iris is a magnificent group of iris native to Asian countries. The blooms are usually huge, ruffled and flat in form. The colors are usually marbled gray or white. They are the other beardless irises. Japanese irises are adaptable to a variety of environments as long as basic needs are met. It prefers a moist acidic, full sun location. A heavy loam to maintain moisture is required. Best growth occurs with a pH between 5.5 and 6.5.  Fertilizing should be liberal with a balanced fertilizer of 10-10-10 in the spring and just before bloom. Division should take place every 3-4 years and the plants moved to another location.  Something other than iris should be planted in that location.  JIs secrete something into the soil that lessens vigorous iris growth for a time, unless a lot of water leaches through that soil, such as at the edge of a stream or under a waterspout. The rhizomes of beardless iris are finger sized, densely crowded, and covered with coarse fibers, while a mass of thick, abundantly branching white roots spring from the underside.

Here in New England many of the iris species can be grown with  success under most conditions with understanding and planning. The best time to plant iris is late summer through early fall. Early fall is emphasized because the rhizome requires at least 6-8 weeks to establish itself before the ground begins to freeze and growth is halted. Adhering to this schedule can insure blooms for the following season. I learned this from experience.  Many a time I had to wait two seasons to see a bloom on a new plant. For best growth and bloom, irises need at least a half- day of full sun. Bearded irises prefer a balanced well-drained soil, and a pH of 6.8-7.0. Heavy clays require amending with gypsum or coarse sand to aid drainage. Iris can be mulched lightly for winter protection, avoiding heavy mulching to the rhizome area, but the mulch must be removed quickly in the spring to avoid rot. The rhizome likes to breathe. When planting add a dash of superphosphate or bone meal and mix in well to the soil. It can aid in establishing the plants root growth. Start with digging a 3” hole about 6” in diameter. In the center make a small fist size mound of soil. Place the rhizome on this mound and distribute the roots around this mound. Fill in the soil. This will allow about 1/3 of the rhizome to be showing above the soil and anchor the plant by the roots. Plant the rhizomes 14” to 18” apart. This will allow good air circulation around the plants during the growing season and aid in reducing fungus and rot. In mid April a fertilizer low in nitrogen will help with the growing season. A 6-10-10 is generally recommended. Another dose is recommended after fall dividing to help the plant through the winter and give it a boost in the spring. Bearded irises are drought tolerant plants. Avoid watering unless necessary. Constant moisture can lead to rotting leaves. Keep your iris beds weed free to help with air circulation. This helps avoid leaf spot problems and rots. Divide bearded iris every three years.

In the fall cut the leaves back on all irises at the end of October or beginning or November. By this time the larvae of the iris borer is established and you are reducing the possibility of a problem for the following year. Destroy the debris. Do not add debris to your compost pile. Pupae of the iris borer moth are about 1” long and shiny brown and found in the soil in late summer and early fall. In the fall the pupae develop into moths which lay eggs on iris foliage and other garden debris. By following the suggested timing, you remove a potential spring problem that will not be discovered until later in the growing season. If not prevented, the larvae will hatch grubs that bore down into the plant the next spring and eat the rhizome from the inside out. A spongy wet looking middle leaf will emerge if the borer has invaded the plant.  The iris borer can be killed by hand in May and June by squeezing infested leaves between the thumb and forefinger in the vicinity of the injury or poking the rhizome with a piece of wire.  If rot has occurred either due to too moist conditions or borer injury dip the trimmed-undamaged portions in a solution of one-part household chlorine bleach and ten parts water and soak for 24 hours to kill bacteria.

Finally, the bulbous irises should be mentioned. In the past they have not enjoyed wide popularity but that is changing. The first iris to bloom each season is the Iris reticulata, a bulbous iris. They are small like a crocus with a 2”-3”diameter and grow a few inches above the ground. They are blue and violet in color but there are yellow species. The florist’s irises are the Dutch hybrids. Bred from species found mostly in Spain, Portugal, and Morocco. These bulbs are inexpensive, easy to grow and deserve more attention. At this time the American Iris Society does not recognize the bulbous iris.

Many books on iris are available. Some of my favorites include The Gardener’s Iris Book by William Shear, A Handbook of Garden Irises by W.R. Dykes and The Japanese Iris and The Siberian Iris both by Currier McEwen.

For other articles, check out our archives

Provided by the Western Massachusetts Master Gardener Association
www.wmassmastergardeners.org.