Iris ensata Illumination - Japanese Water Iris

Iris ensata 'Illumination' is a variety of Japanese water iris, quite rare in cultivation, which lives up to its name. This plant, of beautiful stature, offers large particularly bright flowers: open flat, they are a vivid blue-violet, illuminated by a wide white centre and adorned with a small yellow flame in the centre. Plant this rhizomatous perennial in moist soil, for example on the banks of a pond or in good loamy soil that never dries out in summer. It can be grown in full sun or light shade, in acidic to neutral soil. Stunning when planted en masse near water features, Iris ensata also offer beautiful flowers for bouquets.  

Iris ensata (synonym kaempferi), known as hanashōbu in Japanese, are not comparable to our classic garden irises, except for their membership in the Iridaceae family. The original Iris ensata is a fibrous rhizome plant native to Asia, specifically the wetlands of Japan, the Himalayas, and Siberia. These irises, known for being difficult to grow, like acidic and peaty soils (cannot tolerate excess limestone), are thirsty for water during their growing and flowering period, but appreciate slightly less humid soils in winter: they are found in nature growing above the water level, which often drops in winter and rises again in spring with the melting snow. 

The 'Illumination' cultivar forms an erect, bushy clump, reaching 1m (3ft) in height when in flower (70cm (28in) for the foliage) with a spread of 50 to 60cm (20 to 24in). The plant slowly spreads on the ground through its rhizomes, becoming more beautiful year after year. The deciduous foliage, of medium green colour, consists of long and slender ribbon-like leaves, sheathing at the base, marked by a prominent central vein. Flowering takes place between June and August depending on the climate, lasting for 3 good weeks. Flowering stems emerge from the leaf clumps. Each stem carries 2 to 3 large flowers, 12-15cm (5-6in) in diameter. They are composed of 3 large rounded and flattened sepals, topped with 3 equally wide and flattened petals. The heart of the flower is occupied by 3 small upright petaloid styles, pale blue-mauve infused with white. 

Often grown on the banks of ponds and basins, Iris ensata, like many marsh plants, can live with their "feet" in the water during the summer, but their rhizomes do not tolerate being submerged during winter, especially if it is freezing. In our gardens, these Iris ensata will thrive in loamy soil enriched with compost, but not drying out in summer. Plant them, for example, in heavy soil forming a slight depression, at the bottom of a slope, or on a bank where the soil becomes moist through capillarity. Combine Iris ensata 'Illumination' with Anemone rivularis, Daylilies, Darmera peltata, Lobelia 'Queen Victoria', Astilbes, Physostegia virginiana, loosestrifes, and Ligularias. 

Excellent cut flowers, particularly used in ikebana, Iris ensata were once extensively cultivated in Japan for this purpose, especially around Edo (the ancestor of Tokyo).