Iris ensata Diamant - Japanese Water Iris

Iris ensata 'Diamant', with its beautiful flat flowers of pure white adorned with a small yellow macule, is a variety of Japanese water iris that is as elegant as it is bright. Unlike our garden irises, this rhizomatous perennial is comfortable in non-calcareous and waterlogged soils in summer. Beautiful 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), hanashōbu in Japanese, better known as Japanese water iris, 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 wet areas in Japan, the Himalayas, and Siberia. These irises, known to be difficult to grow, love 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 can be found in nature growing above the water level, which often drops in winter and rises again in spring with the melting snow.

The 'Diamant' cultivar forms an erect, rather upright clump, reaching about 80cm (32in) in height when in flower and spreading about 40cm (16in) wide. 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 and marked by a prominent central vein. Flowering occurs between May and August depending on the climate, lasting for 3 weeks. Flower stems emerge from the tufts of leaves. Each stem bears 2 to 3 large flowers, 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 live with 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 loamy 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 'Diamant' with Anemone rivularis, daylilies, Darmera peltata, Lobelia 'Queen Victoria', Astilbes, Physostegia virginiana, Lysimachias, and Ligularias.