Iris ensata Sugar Dome - Japanese Water Iris

Iris ensata 'Sugar Dome' is a Japanese water iris that produces large, unusual double flowers with enormous undulated petals in a soft violet-blue colour veined with white. It is a mid-season variety that typically blooms in July. Unlike our garden irises, this rhizomatous perennial is comfortable in non-calcareous and waterlogged soils in summer. They look stunning when planted en masse in wet areas and along the banks of water bodies. In the past, Iris ensata were extensively cultivated in Japan, especially around Edo (the ancestor of Tokyo), for cut flowers.

Iris ensata (synonym kaempferi), known as hanashōbu in Japanese, commonly referred to as Japanese water iris, bears no resemblance to our classic garden irises, except for being part of the Iridaceae family. The original Iris ensata is a fibrous rhizome plant native to Asia, specifically in the wetlands of Japan, the Himalayas, and Siberia. These irises, known for being difficult to grow, prefer acidic and peaty soils (can't tolerate excess lime), require ample water during their growth and flowering period, but appreciate slightly drier soils in winter: in the wild, they can be found above the water level, which often decreases in winter and rises again in spring with the melting snow.

The cultivar 'Sugar Dome' is a horticultural creation by Bob Bauer and John Coble dating back to 2008. This excellent variety has been recognized in dedicated competitions (Honorable Mention 2011, Award of Merit 2013, Payne Medal 2015). The plant forms an upright, rather erect clump, reaching approximately 1m (3ft) in height when in bloom, with a spread of 50cm (20in). This iris slowly spreads on the ground through its rhizomes, becoming more beautiful with each passing 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. The non-remontant flowering occurs in summer, varying in timing depending on the climate. Flower stems emerge from the leaf clumps, each bearing 2 to 3 very large flat flowers measuring 15cm (6in) in diameter. Each flower consists of 6 large, flat, undulated sepals, topped with 3 much smaller petals and 3 erect styles. The sepals are a medium blue mixed with light blue on the edges and veined with white. The small petals are white, frilly, infused with a soft lemon yellow colour. Bright yellow signals illuminate the centre of the flower.

Often grown 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 don't tolerate being submerged during winter, especially if it's freezing. In our gardens, these Japanese irises will thrive in well-drained, loamy soil enriched with compost, but not drying out in summer. For example, plant them in heavy soil forming a slight depression, at the bottom of a slope, or on a bank where the soil becomes moist through capillary action. Combine Iris ensata 'Sugar Dome' with Anemone rivularis, Darmera peltata, Lobelia 'Queen Victoria', Astilbes, Lysimachias and Ligularias for example.