Plant Profile: Iris Japonica

With a few exceptions, the forms of Iris most familiar in European contexts require open conditions and full sun to thrive, making them difficult to incorporate into urban plantings that rely on a closed vegetation cover to achieve weed suppression and minimise maintenance. However, there are a number of useful Iris species that prosper in more crowded conditions and which offer considerable landscape potential yet are currently little used.

One such plant is the low-growing East Asian Iris japonica, native to Japan and China, where it occurs at woodland edges and in open grassy meadows. In spring, distinctive sprays of fringed pale lilac flowers with yellow crests float on branched stems above glossy mid-green foliage in a manner reminiscent of orchids, earning it the nickname ‘butterfly flower’. The sword-shaped leaves emerge in fans from short rhizomes, from which slenderer creeping rhizomes extend to colonise adjacent ground, eventually forming an effective evergreen ground cover. It favours humus-rich soils, but like most Iris, it is drought tolerant once established; poor winter drainage may cause roots to rot.

Adapted to partial shade, I. japonica lends itself well to sheltered urban pocket plantings in the shade of buildings or beneath the canopy of street trees, combining effectively with ferns and other loose ground covers to provide striking early-season interest.

But as its varied natural habitats suggest, it is also potentially valuable in extensively managed plantings in more open settings: the American designer and nurseryman John Greenlee is a proponent of its use in designed meadows, where its spring flowers are held advantageously above the growing grasses. Hardy to approx. -15°C, the species is highly variable over its wide geographic range, and some recent selections — notably the striking ‘Eco Easter’ from the US breeder Don Jacobs—are reported to be hardier.”

By Martin Deasy, a tutor on the RHS Mhort. He also runs his own landscape design business.

This article was first published in the July-August 2023 edition of FloraCulture International.