Japanese iris (Iris ensata), an herbaceous perennial native to Japan, produces huge, ruffled, beardless blooms in shades of blue, violet and white. The flowers appear on upright flower stalks in early to mid-summer. The narrow foliage reaches up to 4 feet in height and adds elegance to the garden even after the blossoms fade. Japanese iris also thrives in wet conditions and makes the perfect addition to water and bog gardens, and plantings along ponds and streams. Hardy in Zones 5 through 9, Japanese iris performs well in most areas of the United States with only minimal care.
Plant Japanese iris anytime from spring to fall, though planting in late summer after flowering ends yields the best results. Choose a site that receives full sunlight throughout the day and consists of heavy, rich soil. Spread a 2-inch layer of manure over the planting site and use a garden spade to work it into the soil to increase fertility before planting.
Dig two trenches about 2 to 4 inches deep with a ridge between them at the planting site. Place a rhizome directly onto the ridge and spread the roots out into the trenches. Cover the roots and rhizome with soil, leaving about 1 inch of the rhizome exposed. Tamp down and water to compact the soil.
Spread a 2- to 3-inch layer of straw mulch over the soil surrounding Japanese iris immediately after planting to reduce the growth of weeds and conserve moisture. Allow about 3 inches between the base of the plant and the mulch to provide adequate air circulation.
Water Japanese iris once every five days to keep the soil moist at all times. Soak the soil to a depth of at least 6 inches each time to ensure the roots absorb plenty of water. Never allow the soil to dry completely, as the plant cannot tolerate dry soil conditions.
Feed your Japanese iris plant twice per year, once during earlier spring and again just before blooming begins in summer. Apply a balanced 12-12-12 NPK fertilizer formulated for flowering plants, following the manufacturer's directions for the best results.
Remove old, faded flowers and stalks whenever possible to encourage additional flowering instead of seed formation. Remove entire stalks and their flowers, as hewed growth promotes the development of disease. Hewed growth refers to leaves or stalks severed above the ground, leaving the fleshy interior exposed.