Species Iris, 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 caricifolia
Synonym:Iris doniana
Synonym:Iris kaempferi
Synonym:Limniris ensata
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Japanese (JI)


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:

Medium Purple

Bloom Time:

Very late (VLa)



Other details:

Unknown - Tell us

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):

Unknown - Tell us

Foliage Color:

Unknown - Tell us

Bloom Characteristics:

Unknown - Tell us

Water Requirements:

Requires consistently moist soil; do not let dry out between waterings

Very high moisture needs; suitable for bogs and water gardens

Where to Grow:

Unknown - Tell us


This plant is said to grow outdoors 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


Tangent, Oregon

Wilkes Barre, Pennsylvania

Coppell, Texas

Port Lavaca, Texas

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Gardeners' Notes:


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.


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 ... read more


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.