Water iris is a group of flowering iris that can grow well and thrive in either moist to boggy soil or in shallow water up to 3 inches over the crown of the plant. There are several iris cultivars that have this planting flexibility including iris laevigata and iris pseudacorus. They should be pruned in the summer or early fall after blooming only as needed to deadhead spent flowers or remove damaged or diseased foliage.
Remove wilted iris flower heads on their short stalks after the bloom has faded and begun to die back. Repeat this process throughout the growing season to keep the stand looking tidy. Place the cut just at the bottom of the flower stalk but leave the surrounding and lower foliage that encases the flower stem in place. Lift the cut spent flower heads out of the plant canopy and compost or discard.
Prune water iris foliage that is damaged, appears diseased or is discolored by cutting just the damaged leaf down to the crown of the plant. Leave all healthy foliage in place to capture sunlight and feed the underground rhizome. Pull the ailing leaves that have been cut from the plant and discard in the trash to prevent the spread of disease or pest activity.
Prune water iris foliage down to one half to one third of the plant height before digging and dividing the rhizomes in the early fall. This will reduce stress, shock and die back once the rhizomes are transplanted in their new location.