The huge ruffled dinner plate size flowers of the Japanese iris have been developed over centuries in Japan. They have been developed from one species I. ensata. The species has fairly wide falls which hang down and small narrow upright standards. The color is a deep red violet or maroon. They are still sometimes referred to as I. kaempferi which was the former name of the species I. ensata. It has probably been cultivated in Japan for over 500 years. They are referred to as hanashobu in Japan. You may also hear the terms Edo, Higo and Ise used to classify Japanese irises. Following is a brief description and history of these three types of Japanese irises.
When Japanese irises were first cultivated in Japan there were many color variations of the species found in the Asaka marshes near Tokyo that are not known today in the wild. These were collected and hybridized. They were raised in fields and had to withstand the rigors of an outdoor garden. They had a wide range of colors and patterns but were more simple in form. These became known as Edo varieties, Edo being the old name of Tokyo.
In the Kumamoto Prefecture the Edo strains were being bred but due to the heavy rain in this area the plants were bred to be enjoyed indoors. There were elaborate traditions associated with the manner in which these iris were displayed. These came to be known as Higo strain and were bred for white and strong colors, with none of the patterns or pale colors found in the Edo strains.
The Edo and Higo strains with their heavy substance were in stark contrast to the very delicate Ise varieties. The Ise iris were hybridized from species collected in Ise‑Matsuzake district on Honshu. They were associated with religious shrines and their form was very controlled. The flower had to have three falls that were wide, overlapping and hung downward. The standards were erect, at a pleasing angle, and the style crests finely toothed to give the bloom a feeling of delicacy. Only pale colors were used, often pink shades. Like the Higo varieties they were bred to be viewed indoors and the Ise often do not have enough substance to stand up in outdoor gardens.
Our western hybridizers have taken both the Higo and Edo strains, and occasionally the Ise, to develop our wide range of Japanese irises. The flowers come in all shades of blue, red violet, purple and white. They often have interesting patterns of dots, stripes, veining and rims in contrasting colors. The form can be similar to the old Ise form with three falls or can have six, nine or twelve falls. Often the styles are expanded to form a fluff in the center of the flower. The flowers can be tailored or ruffled, flat and flared or pendant. Often the flowers can be eight to twelve inches in diameter. Truly spectacular!!
These spectacular irises are surprisingly easy to grow if you pay attention to a few of their requirements. It is a common but mistaken belief that Japanese Irises need to grow in water. In fact in cold climates they do not like to be in water in the winter. They will do just fine in ordinary garden conditions as long as they are given sufficient water through the growing season, about one inch a week if there is insufficient rain. Japanese irises prefer a position in full sun and require an acid soil rich in organic materials. Our soils in the Puget Sound area are usually about the right acidity, between 5.5 and 6.5 in PH. Japanese irises will not grow in alkaline soil so never add lime. Many people like to use bone meal as a fertilizer and soil amendment, never use it on Japanese iris as it has an alkaline reaction and will stunt or even kill them. Japanese irises are very heavy feeders and require a liberal application of balanced fertilizer such as a 12‑ 12‑12, in spring and just before bloom time.
Early fall is the best time to plant Japanese irises so they have time to establish new roots before cold weather. When planting Japanese iris plant strong divisions and do not allow the roots to dry out. Plant the rhizomes one to two inches deep in a slight depression. Since the rhizomes form new roots on top of the old, planting in a depression allows you to fill with soil around the plants to keep them growing vigorously for a longer period. Japanese irises will literally grow out of the ground if not transplanted often enough. It is recommended that they be reset every three to four years. Do not fertilize newly planted irises. At the time of planting the roots can be burned by fertilizer. Wait for a few weeks to feed them until you see new growth. A mulch of two to three inches is recommended to help conserve moisture and protect from winter heaving especially on plants that are planted late in the fall.
These spectacular irises are easy if you just remember to give them ample moisture, acid humus rich soil and generous feeding. Good culture is more important to Japanese irises than to other types of irises and they will be taller, more floriferous and have larger flowers if given good care.