Iris ensata Activity - Japanese Water Iris

Iris ensata 'Activity', with its large flat flowers of pure white adorned with a small yellow macule, is a variety of Japanese water iris as elegant as it is bright. Unlike our garden irises, this rhizomatous perennial is comfortable in non-calcareous and waterlogged soils in summer. Superb when planted en masse in wet areas and on the banks of water points, Iris ensata were once intensively cultivated in Japan, especially around Edo (the ancestor of Tokyo), for cut flowers.

Iris ensata (synonym kaempferi), known as hanashōbu in Japanese, are more commonly referred to as Japanese water iris, and have nothing in common with our classic garden irises, except for their belonging to the Iridaceae family. The original Iris ensata is a fibrous rhizome plant native to Asia, specifically to humid areas of Japan, the Himalayas, and Siberia. These irises, known for their difficulty in cultivation, prefer acidic and peaty soils (they do not tolerate excess lime), are thirsty for water during their growing and flowering period, but appreciate slightly less moist soils in winter: they are found in nature growing above the water level, which often decreases in winter and rises again in spring with the melting snow.

The cultivar 'Activity' forms an erect, rather upright clump, reaching about 60cm (24in) in height when flowering and 40cm (16in) in width. The plant slowly spreads on the ground through its rhizomes, becoming more beautiful year after year. The deciduous foliage is composed of long, slender, sheathing leaves with a prominent central vein. Flowering takes place between May and August, depending on the climate, lasting for 3 weeks. Flower stalks emerge from the leaf clumps, each bearing 2 to 3 large flowers measuring 12cm (5in) in diameter. They are composed of 3 large flat sepals with a bright yellow signal at the base, topped by 3 smaller and finer petals.

Often cultivated on the banks of ponds and basins, Iris ensata, like many marsh plants, can tolerate having their "feet" in water during 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 a well-drained soil enriched with compost, but not drying out in summer. Plant them, for example, in a 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 'Activity' with Anemone rivularis, daylilies, Darmera peltata, Lobelia 'Queen Victoria', Astilbes, Physostegia virginiana, loosestrifes, and Ligularias.