Japanese Water Iris (Iris ensata) Growing & Care Guide for Gardeners
Article by Dean Ravenscroft, Ph.D. - Updated 16th Feb 2024
- Plant Characteristics: The Japanese Water Iris boasts vivid, large blossoms in shades of purple, pink, and white. These help to bring a splash of color and a touch of the exotic to gardens, especially around ponds and water features.
- Ideal Growing Conditions: Prefers a moist, acidic soil. Plant at the edges of ponds or in damp spots of your garden. Locate in an area with full sun to partial shade for the best flowering results.
- General Care: Keep soil consistently moist. Following blooming, trim back the foliage. Divide clumps every 2 to 3 years to maintain vigor.
- Tips for New Gardeners: Japanese Water Iris is reasonably easy to care for, making it suitable for novice gardeners. Their unique aesthetic and minimal requirements are a win, but make sure they have a constantly wet soil.
The Japanese Water Iris (Iris ensata) is also known as the Japanese Iris, and less frequently as the Oriental Iris or Hanashobu.
Gardeners like myself love to grow this Iris for its stunning, intricate blossoms. These plants are great for adding a touch of elegance to aquatic settings.
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.
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.
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.
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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.
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.
Can you recommend some good companion plants to grow alongside Japanese Water Iris?
Plants that grow in similar conditions (moist, well-drained soil, full to partial sun) can make good companion plants for the Japanese Iris, you may wish to consider plants such as Astilbe, Lobelia, Hostas, Japanese Primrose, and Swamp Milkweed.
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.
Summary
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.
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