Photo by Melody

PlantFiles: Japanese Water Iris, Japanese Flag, Russian Iris
Iris ensata

Family: Iridaceae (eye-rid-AY-see-ee) (Info)
Genus: Iris (EYE-ris) (Info)
Species: ensata (en-SA-tuh) (Info)

Synonym:Iris kaempferi

» View all varieties of Iris

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Japanese (JA)

24-36 in. (60-90 cm)

18-24 in. (45-60 cm)

USDA Zone 5a: to -28.8 C (-20 F)
USDA Zone 5b: to -26.1 C (-15 F)
USDA Zone 6a: to -23.3 C (-10 F)
USDA Zone 6b: to -20.5 C (-5 F)
USDA Zone 7a: to -17.7 C (0 F)
USDA Zone 7b: to -14.9 C (5 F)
USDA Zone 8a: to -12.2 C (10 F)
USDA Zone 8b: to -9.4 C (15 F)
USDA Zone 9a: to -6.6 C (20 F)
USDA Zone 9b: to -3.8 C (25 F)

Sun Exposure:
Full Sun
Sun to Partial Shade

Parts of plant are poisonous if ingested

Bloom Color:

Bloom Time:
Very late (VLa)


Other details:
Requires consistently moist soil; do not let dry out between waterings
Very high moisture needs; suitable for bogs and water gardens

Soil pH requirements:
6.1 to 6.5 (mildly acidic)
6.6 to 7.5 (neutral)
7.6 to 7.8 (mildly alkaline)

Patent Information:

Propagation Methods:
By dividing rhizomes, tubers, corms or bulbs (including offsets)

Seed Collecting:
N/A: plant does not set seed, flowers are sterile, or plants will not come true from seed

Awards (if applicable):
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3 positives
No neutrals
No negatives

Gardeners' Notes:

Positive coriaceous On Feb 20, 2015, coriaceous from ROSLINDALE, MA wrote:

Japanese iris are hardy in Z4, some say Z3.

They are famously intolerant of alkaline soils. Optimal soil pH is 5.0-6.5. Above 6.5, they turn cholorotic (the leaves turn yellow).

They tolerate flooding when in bloom, but their requirement is for consistent moisture, not wet soils. They do well in well-drained soil and typical border conditions as long as it's never droughty.

Positive annlof On Mar 21, 2011, annlof from Camarillo, CA wrote:

Iris ensata blooms for a short period in midsummer. Some cultivars have flowers as big as dinner plates, and some are a true vivid blue -- absolutely stunning! It's probably one of the last irises to bloom (early July in New England.) This iris thrives in bogs but also does quite well in a sunny border with good, deep loam.

I had success with Japanese irises when I lived in Maine. Since then I have moved to Southern California, and have not attempted to grow them here.

I have to disagree with the culture sheet above which states that iris ensata tolerates "mildly alkaline" conditions. I've always understood that this plant is a true acid lover which can't tolerate lime in any form. For gardeners in alkaline-soil areas, it's generally recommended that plants be grown in pots (with a peaty potting mix) and left sitting in a saucer of water. However, be aware that your tap water might be alkaline too so watering with rainwater or distilled water would be preferable.

Positive ladyannne On Jul 29, 2006, ladyannne from Merced, CA (Zone 9a) wrote:

We place these in pots, cover with large rocks and pop them in our ponds and waterfalls. Reliable, startling early spring colour. I collected the seeds this year, and will be experimenting with them.


This plant has been said to grow in the following regions:

Canoga Park, California
Fremont, California
Huntington Beach, California
Merced, California
Sacramento, California
San Leandro, California
Santa Maria, California
Barbourville, Kentucky
Bath, Maine
Jamaica Plain, Massachusetts
Blue Springs, Missouri
Neptune, New Jersey
Buffalo, New York
Southold, New York
Mount Gilead, North Carolina
Mount Hood Parkdale, Oregon
Tangent, Oregon
Wilkes Barre, Pennsylvania
Coppell, Texas
Port Lavaca, Texas

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