Iris ensata or Japanese iris, are beardless and bloom from late June to July in the Northeast.
With thinner leaves than its bearded cousins and a rib that runs the length of the leaf, the hybridized plant that we know produces beautiful flowers in shades of blue, red violet, purple and white. In Japan the plant is known as 'Hanashobu'.
Native to Japan this species of iris was introduced to the United States in the 19th century, becoming popular after the turn of the 20th century, falling out of favor during the Great Depression and World War II, the plant began to gain interest again in the last 20 years.
Plant the rhizomes in very moist soil where they can be kept watered even in drought conditions. The pond bog area is an excellent place for them with rich soil and slightly acidic pH between 5 and 6.5. Divide every three to four years for good flowering and because the new roots grow above the old and will rise out of the soil in that time frame. If planted in full shade, the blooms will not be as numerous. Transplanting in September seems to work well, giving the rhizomes enough time to acclimate prior to the onset of winter.
Remove the leaves as they die to help control disease and pests such as Borers that will winter in the debris created by dying leaves and eventually bore into the soft leaves of Spring and on down to the rhizome. First signs are yellowed leaves at their base, easily removed and black at the end.
In the cold climates, it perhaps is best to plant the Japanese iris in pots that can be removed from the pond once the weather turns cold. The plant does not like being in the water when it is -20 degrees, but will do alright on land with little water during the winter. Be sure to plant in fabric pots with soil that will not float into the pond once placed in the spring.
This beautiful plant will give you much to appreciate and will enhance the overall appearance of any landscaped pond.