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Iris: Japanese Iris

Updated on January 18, 2017
OldRoses profile image

Caren White is a Master Gardener and instructor at Home Gardeners School. She has been a volunteer at Rutgers Gardens for over a decade.

Purple Japanese Iris
Purple Japanese Iris | Source

Japanese iris (Iris ensata) may look exotic, but they are easy to grow. As their name implies, they are native to Japan where they have been grown and bred for 500 years. Japanese iris are beardless iris like their cousins, the Siberian iris, but their flower petals are larger and flatter, hence their nickname Butterfly Iris. The flowers range in color from purple to blue to pink to white and many bi-colors. They bloom at the end of the “iris season” after the Siberian iris, normally in mid- to late June. Their leaves are thinner and more grass-like than the bearded iris. They are also slightly shorter, about 40” tall. Japanese iris are hardy in USDA growing zones 4-9.


Japanese iris require a minimum of 6 hours of full sun each day. In warmer climates, shade in the afternoon is preferred to keep them from drying out. They like moist, well-drained soil that is more on the acidic side. They are often planted on stream banks, their natural habitat, where the soil remains constantly moist. They are not pond plants, however. Their crowns must remain above the water line. Areas with a high water table are also good choices for planting your Japanese iris.

Japanese iris can be planted any time from spring until fall. Don’t allow your rhizomes to dry out before planting them. Soaking them overnight before planting is a good idea. Plant them so that the tops of their rhizomes are at least one inch below the soil surface. Keep your plants well mulched to make sure that the soil remains cool and moist and to keep down weeds.

Japanese iris are what is known as heavy feeders, rapidly depleting the soil of essential nutrients. It’s a good idea to fertilize them every year, either right before they bloom or just after they bloom. Use the same fertilizer that you would use on your acid loving plants such as azaleas and rhododendrons.

Bicolor Japanese Iris
Bicolor Japanese Iris | Source


It’s a good idea to divide your plants every 3 to 4 years to maintain good health. You will notice that your iris clumps expand upwards each year because new roots grow above the old roots consequently forcing the bulbs upwards towards the top of the soil where it is dryer . You should divide your clumps before they reach that point which is unhealthy for them. Spring is the best time to divide and replant your iris. Divide them be carefully digging up the rhizomes about a month after they finish blooming and cutting them apart. Replant the outermost, young rhizomes and discard the older center ones. Replant them with the tops at least one inch below the soil surface. If you are not going to be replanting your rhizomes immediately, keep them moist by storing them in bucket of water until you are ready to plant them. Smaller divisions can take up to two years to reach a size where they will bloom so be patient!

Cut Flowers

Japanese iris make excellent cut flowers. Harvest your flowers early in the day. Choose buds that are just beginning to open rather than flowers that are fully open. The buds will open in a few hours in the vase. Place your flowers in a bucket of tepid water until you are ready to create your arrangement. When you are ready to arrange them, re-cut the stems about an inch above the original cut at an angle. To ensure the longest life for your flowers, keep your arrangement out of direct sunlight. It’s also a good idea to place it away from drafty doors and windows. Be sure to remove dead and dying flowers promptly.

Add an exotic look and prolong the iris season by planting Japanese iris. They are hardy, easy to grow plants for the moister areas of your yard.

© 2015 Caren White


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    • OldRoses profile image

      Caren White 2 years ago from Franklin Park, NJ

      Flourish, I'm knee deep in catalogs and counting the days until spring. Thanks for reading and commenting.

    • FlourishAnyway profile image

      FlourishAnyway 2 years ago from USA

      You have me looking forward to Spring!

    • OldRoses profile image

      Caren White 2 years ago from Franklin Park, NJ

      Sorry Will, but Japanese iris require moisture. They are best grown in wet soil.

    • WillStarr profile image

      WillStarr 2 years ago from Phoenix, Arizona

      Can they be grown in the Arizona desert? We live in Phoenix.

    • OldRoses profile image

      Caren White 2 years ago from Franklin Park, NJ

      Heidi, so sorry that you can't grow iris. They are one of my favorite flowers. Thanks for reading, voting and commenting.

    • heidithorne profile image

      Heidi Thorne 2 years ago from Chicago Area

      Irises are lovely, but I've never been able to grow them successfully. I think it's a soil quality issue. Thanks for the info! Voted up, useful and beautiful!