Japanese Water Iris (Iris ensata) Growing & Care Guide for Gardeners

The Japanese Water Iris (Iris ensata) is also known as the Japanese Iris, and less frequently as the Oriental Iris or Hanashobu.

One of the many reasons that gardeners enjoy growing this Iris is for its stunning, intricate blossoms. These can be used to add a touch of elegance to aquatic settings.

Iris ensata Lake Effect
Photograph of Japanese Water Iris 'Lake Effect' Cultivar by F. D. Richards

The resilient nature of these Irises make them ideal for water features and ponds. They can help to enhance biodiversity, and provide a visually captivating focal point.

These hardy perennials bloom in the summer. Japanese Water Irises have sword shaped leaves and bloom with blue, white or purple flowers. These sit atop of 28 to 36 inch (70 to 90 cm) stems.

Iris ensata
Photograph of Iris ensata by TANAKA Juuyoh (田中十洋)

This plant used to be classified by the scientifically as Iris kaempferi, a synonym that is still sometimes used by gardeners.

Iris ensata  Growing and Care Guide

Common Names: Japanese Water Iris, Japanese Iris, Oriental Iris, Hanashobu, Ensata Iris.
Life Cycle: Hardy perennial.
Height: 24 to 36 inches (60 to 90 cm).
Native: East Asia.
Growing Region: USDA Zones 4 to 9; thrives in warmer climates, can survive to extremes of -30°F (-34°C). RHS H5, considered hardy to temperatures of around -15°C (5°F).
Flowers: Summer.
Flower Details: Blue, pink, purple, lavender, red, white. Often marked with a contrasting central yellow or white signal. Bi-colored. Co-pigmented. No beards.
Foliage: Sword-shaped. Ribbed leaves.
Sow Outside: 1/4 inch (6 mm). Seeds should first be sown into flats in the autumn or winter. Next sink the flat into the ground in an area that offers shade, preferably close to a wall that faces north. Provide a glass/plastic covering. Keep an eye on the flats to ensure that the soil remains moist. After five weeks bring indoor and keep at a temperature of 60 to 70°F (16 to 21°C). Put flats outside again before the last frost of spring. Provide a regular feed for the growing seedlings. Transplant Iris seedlings in late spring if they look strong or in the autumn (plant in a depression shaped like a saucer).
Sow Inside: Germination time: one to eighteen months. Can be done anytime of the year. Mix Iris Kaempferi seeds in a moist growing medium, wrap in a plastic bag, then stratify by refrigeration for five weeks. Next sow the seeds into a flat and keep at 60 to 70°F (16 to 21°C). Seedlings can be transplanted into a three to four inch (7 to 10cm) depression in either spring or autumn.
Requirements and care: Full sunlight or partial shade. Soil pH 5.0 to 7.0. Enriched soil. Heavy soil. Wet/moist soil. Provide a liquid manure feed fortnightly whilst growing. Alternatively use a supply of 10:10:10 Rapid Gro or Mir-acid of camellia. Maintain vigor through dividing in the autumn every three to four years. Use mulch to help keep the soil moist. Propagate: by dividing tubers following flowering.
Miscellaneous: Rejuvenate by potting in a mixture of 30% to 50% cow manure: 50 to 70% soil. Place the pot in a two inch (5 cm) deep pool of water. It should take just over a month for the plants to develop new roots. Once the roots are strong, replant in the garden.

How to Grow Japanese Water Iris

Japanese Water Iris can be started outdoors from seed in flats. Sow at a depth of 6 mm (1/4 inch) in the autumn or winter.

Locate the flat in a shady part of the garden.

Leave the flat exposed to the elements for a month or so in a shady part of the garden (the seeds require frost stratification)

Once stratified, bring the flats indoors until the spring. Move the flats outdoors again, and once seedlings appear, provide with a feed.

You can transplant the young plants to their final location in early autumn. Use a spacing of about 25 cm (10 inches).

Plants will grow well in both sunny locations and in areas of the garden that have partial shade.

These Irises like to grow in a soil that is rich, has a slightly acidic to neutral pH (5.5 to 7), and is damp.

The germination of Japanese Water Iris can take anything from one month to one and a half years, so patience is required to grow from seed.

Japanese Water Iris Propagation

If you require further plants, and don't have seed, then you will probably need to hand pollinate the flowers. Once seed as set, sow as described above.

Alternatively you may wish to propagate by dividing the tubers once flowering has completed in late summer, or early in the autumn.

Propagation through of division is a lot less hassle. Simply dig up the clump, give the soil a rinse. Then separate the rhizomes by hand (you may need to use a sharp gardening knife for this step). Each division you make should have at a strong fan of leaves and strong roots. Trim the leaves to about a third of their size. Plant the division into its new location, with the rhizome fractionally below the soil surface. Make sure the new plant is kept moist.

Japanese Water Iris Care

It is necessary to feed then with liquid manure. Divide every four years to maintain strong plants.

If growing as a water garden feature, then grow at the margins where the water is not as deep. Despite being associated with water, they will thrive in a soil with good drainage.

Common Questions

Is Iris ensata a good plant to use in the garden and/or for landscaping?

Iris ensata can make a great plant for using in gardens and for landscaping. It has stunning, intricate blossoms, and can be used for aquatic landscape settings.

Is Japanese Water Iris fragrant?

Japanese Water Iris is not particularly known for its fragrance.

What is the best Garden location to grow Iris ensata?

Use a garden location that is exposed to full to partial sunlight. Ideally grow it at the margins of water features and ponds.

Is Iris ensata invasive in the USA, if so in which states?

Iris ensata is not generally thought to be an invasive plant the USA.

How do I remove Iris ensata from my garden?

To remove Japanese Water Iris from you garden. First dig around the plant and lift the rhizomes out of the ground. You will need to make sure that you remove as much root material as possible to prevent re-growth. Keep and eye on the area and remove any regrowth.


Iris ensata, the Japanese Water Iris, is a perennial plant valued for its delightful blossoms. This Iris plant is native to Japan, and thrives at the edges of water features and ponds. Grow in areas exposed to full to partial sun. For optimal growth, ensure soil remains moist.

I hope that you enjoyed this guide on how to grow Japanese Water Iris plants. You may also enjoy my gardening guides on how to grow Fothergilla gardenii, Lima Bean plant, and Echinacea purpurea plants.