Japanese iris – planting, care and tips

Japanese iris (Iris ensata)
Japanese iris (Iris ensata) - CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=185853

The Japanese iris is quite demanding, but it rewards the hobby gardener with magnificent, reddish-purple flowers, which a real eye-catcher. Here you find what to consider when planting and caring for.

Profile of Japanese iris:

Scientific name: Iris ensata

Plant family: iris family (Iridaceae)

Other names: Japanese water iris

Sowing time: spring

Planting time: April to May

Flowering period: June to July

Location: sunny

Soil quality: sandy to loamy, nutrient rich, humus rich

These information are for temperate climate!

Use in: pond planting, bouquets, natural garden, water garden

Winter hardiness: hardy, USDA Plant Hardiness Zones: 5 (-26 °C / -15 °F)

Bee and insect friendly: Yes

Plant characteristics and classification of Japanese iris

Plant order, origin and occurrence of Japanese iris

The Japanese iris (Iris ensata), occurs from the Caucasus to East Asia. In its natural habitat in Japan, Korea and Northeast China it grows wild in swamps, ditches and in wet, grassy places in nature. The species has been cultivated in Japan for more than 500 years and there are numerous varieties. Sometimes you can still find Iris ensata under its old botanical name Iris kaempferi, named after the German botanist Engelbert Kaempfer (1651–1716). It belongs to the iris family (Iridaceae).

Characteristics of Japanese iris


The Japanese iris forms dense clusters that grow narrow and upright. The wild species reaches a height of 40 to 120 centimeters (16 to 48 in) and about 35 centimeters (14 in) in width.


The grass-like leaves stand stiffly upwards and are reminiscent of a sword.


The Japanese iris has three small dome-shaped petals that point upwards and three broader pending petals. In the large-flowered varieties, the flowers appear rather plate-shaped. The aim of cultivating was to increase the number of hanging petals. Many varieties have six broad hanging petals that overlap horizontally. Varieties with double flowers sometimes even have nine to twelve hanging leaves. Color variants of the reddish-purple flowers are already in the natural form, from whitish with darker veins to shades of blue. Varieties of all shades of white, purple, blue, purple and pink have been cultivated. By cultivating with tetraploid yellow lilies (Iris pseudacorus) one even worked on yellow varieties. But they are not as vigorous. The flowering time of Iris ensata is between June and July.


The species forms capsules.

Japanese iris – cultivation and care


The Japanese iris is a perennial for the swampy water edge zone in full sun.


The soil needs to be really moist during the summer months. During the season, the Japanese iris wants to stand wet. In the winter from November to April, however, drier. In addition, the soil should be acidic. If you have calcareous soil, it is advisable to sink Iris ensata in a bucket or tub into acidic substrate by the water. In this way, you can also water rainwater in a targeted manner if the water is hard.

Planting Japanese iris

The best time to plant young plants is April and May. If you want to transplant older specimens of this iris species, this is best done in September / October. With every planting, an initial fertilization with organic fertilizer is beneficial.


After budding in spring, you can use a low-nitrogen complete fertilizer. If your garden does not offer optimal location conditions, place Iris ensata in buckets with drainage holes. There are special soils for marsh plants. But you can also use peat or rhododendron humus. At the beginning of the season in May, the buckets are buried at the edge of the pond or near the water so deep that they can be flooded. They are taken out again in autumn. A cut is not necessary with the Japanese iris.


If the cluster is too dense, the root rhizomes hinder their growth. This is why Japanese swamp lilies are divided after two to four years, preferably at the beginning of September. First cultivate the pieces individually in the pot and plant them out in spring. Remember to keep the freshly potted plants sufficiently moist.


The easiest way to propagate Japanese iris is to divide it. To do this, dig out the rhizome outside of the flowering period and divide it into roughly equal pieces, each of which must have at least one eye.

The pure species can also be propagated by sowing the ripe seeds. However, the minimum germ temperature is 22 °C / 71.5 °F.

Diseases and pests

The Japanese iris has hardly any problems with plant diseases and pests in a suitable location. However, the large-flowered lilies react with chlorotic leaves on calcareous soil.


Keep your Japanese iris in the bucket, place the hardy perennials and planter in a protected, drier place in October and cover the plants with a layer of leaves.

Use in the garden

The Japanese iris is ideal for group planting at the water’s edge and fits in moist beds. You can mix the different varieties very nicely. Incidentally, the varieties also make great cut flowers.


Japanese iris is often offered as a colorful mix of varieties. A very beautiful, purple-blooming variety is ‘Amethyst’. ‘Sensation’ has a yellow throat on the purple flowers. ‘Diamond’ blooms in pure white. A variety with white-green striped foliage is ‘Variegata’.

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