Gardening
Topic for July 2003
Japanese Iris
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By Louise A. Dunphy, Master Gardener Intern |
Iris ensata is a magnificent group of irises that are native to Japan, Northern China, Manchuria, Korea, and Siberia. The blooms are usually huge, ruffled and flat in form; some are marbled with gray or white. They are beardless. They bloom about one month after the tall bearded iris. Here in New England that would be the month of July. We commonly refer to them as Japanese iris or JIs. In Japan they are known as ‘Hanashobu’. Several controversies have come and passed concerning the correct botanical name and species of Iris ensata. Since 1985 the Society for Japanese Irises has officially recognized Iris ensata. Classification in Japan corresponds to geographic location. In the United States classification mostly refers to color and number of petals. Those with three falls and three standards are called singles and those with six are called doubles. They are also referred to as the diploids. In 1979 the first tetraploid (McEwen) Japanese iris was introduced. The tetraploids are stouter, larger and more flaring and are of a greater number of chromosomes.
The earliest mention of a wild Japanese iris comes from a poem in the book Shugyobushu by Jien (1155-1225). It had already enjoyed centuries of collecting and hybridizing by enthusiastic Japanese gardeners when in 1869 it was introduced in the United States. Due to the depression and war in the 1930’s and 40’s the Japanese iris lost favor with American gardeners. Within the past twenty years, it has gained interest again, no doubt because of its beauty.
John Tristan, Director of Durfee Conservatory at the University of Massachusetts, documents in his historic review of Durfee, "....in 1870 Japanese exchange students came to Massachusetts to study, and planted a garden at Durfee to display selected plants of Japan." This could very well have been the first introduction here in Massachusetts of the beloved Iris ensata. Today the tradition of growing and cultivating Iris ensata is strong in Japan (Japanese Iris Garden Society) and here in the United States (American Iris Society sub-group The Society for Japanese Irises). In Japan there are some two hundred large gardens visited by six million people each year. There are thousands of Japanese iris enthusiasts and hybridizers throughout the Unites States.
The Japanese iris is adaptable to a range of environments so long as their basic needs are met. These needs are simple but can be considered time consuming. They prefer a moist, acidic, full-sun location. A heavy loam might be required to maintain moisture. Best growth occurs with a pH level of 5.8, but levels between 5.5 to 6.5 are quite satisfactory. If measurements indicate soil is low in acid, one to two pounds of sulfur or ferrous sulfate per hundred square feet will benefit the soil. It is best to test and treat soil well in advance of scheduled planting. Planting and transplanting can take place at any time if given proper care. September is the popular month here in the United States Here in New England, some advise spring to allow the plants to acclimate before the heavy frosts of the fall. The rhizomes should be planted 2 to 3 inches deep. Plant them in a depression, which will help catch water, then fill the depression with organic mulch.
Regular mulching with compost-containing material such as oak leaves will assist in keeping the pH in good shape; fertilize adequately and retain a moist environment. Ponds and streams are favored sites for planting but not necessary. If soil was amended then it is helpful to regularly test the soil’s pH. At least six hours of sun is needed for good growth. After three to four years, replanting is advised. At the time of division, the iris should be moved to a new location where Japanese iris did not grown before. It appears that JI excrete something into the soil that causes the iris to lose their vigor over time and decline. It is recommended that something other than iris be planted in the soil since other types of iris will grow there but not vigorously. The one exception to this is soil that has a lot of water leaching through it, such as soil under a downspout or by the side of a stream
Japanese irises are heavy feeders. A liberal application of a balanced fertilizer (10/10/10) in the spring and just before bloom is beneficial. Weak plants will be invigorated with an application of a water- soluble acid fertilizer. The preparation of your iris bed with composted manure and peat will be a good start for your JI, but once planted do not fertilize transplants until they have become established.
When photosynthesis is complete for the plant it is time to cut back the leaves as close to the ground as possible and discard. Here in New England that would be late October- early November. Do not compost this debris as it could be harboring pests and diseases.
The removal of leaf waste and other debris will lessen the possibility of pests and disease agents. It is also the first step in the environmentally responsible approach of “Integrated Pest Management.” Borers are the most destructive pests of iris. They winter on the old leaves and debris at base of plant. In the spring they make pinpoint holes and enter the plant. They gnaw out soft tissue between leaf surfaces and work down toward rhizomes. A water-soaked and ragged appearance to the leaf fans becomes obvious. Iris enthusiasts advocate killing the iris borer larvae by hand in May and June by squeezing infested leaves between the thumb and forefinger in the vicinity of the feeding injury. Destroy heavily infested rhizomes, along with the larvae. Poking with a piece of wire can destroy borers in the rhizomes. It is important that you cut away damaged and rotted areas. Soft rot caused by bacteria can become a problem. Dipping the trimmed-undamaged portions in a solution of 1 part household chlorine bleach and 10 parts water. After the larvae become 1 � to 2 inches these borers pupate in the soil. With dark purplish forewings and yellow-brown hind wings, these moths, macronoctua onusta, appear in late August to October, flying only at night. The first visible sign of the borer in a Japanese iris is a yellow leaf at center of plant that easily pulls off at base showing a blackened end.
The local affiliate of the American Iris Society (AIS) is the Western New England Iris Society (WNEIS). Each year the local membership hosts an iris show in the spring. Every other year they host or co-host a summer show that features the Japanese iris. The show in June features all the bearded and beardless divisions as well as species. Then in July they hold the Japanese iris show. This year both events take place in Shelburne Falls at the Shelburne-Buckland Community Center on Main Street in Shelburne Falls. This year the Japanese iris show will take place on Sunday, July 6, 2003. Anyone is welcome to enter. The judging usually starts by 11:00; public viewing of the Japanese iris starts at 1pm. For more information and general rules you can contact ldunphy@aol.com or call 1-413-548-9860. It is a wonderful Sunday afternoon adventure that can also include a walk across the Bridge of Flowers.
A great way to introduce yourself to the vast world of the Japanese iris is to visit nurseries in your community or on-line. You can search on-line by using keywords mentioned in this article. If you are interested in the purchase of Japanese iris, talk with your local nursery dealer. To find one near you check out plantsources.com.
McEwen, Currier, The Japanese Iris, University Press of New England, 1990
Authors footnote!
Several days after this article
was completed and submitted for publication sad news came from
South Harpswell, Maine. Currier McEwen, Japanese iris
extrodinaire and resource for my article passed away at the age
of 101. Currier turned 101 in April and was busy and happy
working in his garden. Two weeks ago he fell at his home and
broke his hip. He appeared to be doing well after surgery but
Monday, June 23rd he succumbed and passed on. Here is what his
close friend and fellow irisarian Ted White wrote:
"Professionally,
Dr. McEwen was a rheumatologist and former dean of New York State
Medical School, having been appointed to that position at the age
of 37. He retired from practice at age 86 to devote full time to
his iris hybridizing. In 1976, in order to devote full time to
his Siberian and Japanese iris hybridizing, Currier gave his
daylily hybrids to Howard
Brooks, who continued his hybridizing lines. Dr. McEwen created
the first tetraploid Siberian and Japanese irises, following his
discussions with the late Orville Fay in the early 1960s. Having
used colchicine in his medical practice, Currier used it to
develop a stunning succession of tetraploid iris introductions.
Over his many years of hybridizing he introduced in excess of 100
cultivars. When a person of Dr. McEwen's stature passes on it
seems almost as if a library of knowledge has burned to the
ground. Fortunately, Currier wrote two books on Siberian irises
and one on Japanese irises. Each is a brilliant distillation of
both species of irises that serve as a testament to the man and
his important contributions in life."