Belonging to the Series Laevigatae, and native to Northern China, Eastern Siberia and Japan, these are better known as Japanese iris, having been collected, bred and cultivated in Japan for centuries. Modern varieties were developed in Japan, probably from a limited gene pool of Japanese origin.

Commonly associated with water, these irises however, do not like to stand in water all year round but should be flooded with water in Spring only. They like a constantly moist, rich acid soil, frequent fertilisation, and an organic mulch. They will grow happily in peaty, damp soil at the edge of a pond, or in a moist garden bed. They also do well in pot culture so long as they are repotted regularly into humus rich, acidic soil. They are very hardy plants, can be grown in light shade, and tolerate cold winters.

The original species type has narrow upright standards and wide, hanging falls. Generally the colour is dark purple, but there are blue, pink and white variants. These are the ‘Nagai’ types. Natural cross pollenation resulted in the flatter ‘Edo’ type named for the Tokyo region where they were often grown. From these the robust ‘Higo’ strain was developed, and these provided ancestors to the modern, or ‘Hanashobu’ form.

Modern forms show much pattern variation, enlarged horizontal standards, multiple petals, and enlargement of style arms. Height is generally 60 to 90cm, and the leaves have a prominent midrib.

Japanese irises can be grown very easily from seed, and seed from quality varieties will produce many lovely seedlings. Work is being done to produce interesting species crosses, one of the most notable being the Pseudata or ‘Eye Shadow’ irises being bred in Japan, from I. pseudacorus, and I. ensata.

[Source: RHS Wisley handbook ‘Irises’ by Sidney Linnegar & Jennifer Hewitt.]