Blue Flag Iris rewards the water’s edge with elegant, true-blue blooms veined in violet and gold, unfurling atop sword-like foliage from late spring into summer. Native to eastern North America, it’s perfectly at home in the damp ground along a pond, stream, or rain garden where many perennials struggle. Reaching two to three feet tall in tidy upright clumps, it brings vertical structure to a sunny border and its blooms are lovely cut for the vase. Butterflies work the flowers, while its spreading roots make it a natural choice for stabilizing soil along banks and slopes. It asks for steady moisture and full sun, and is seldom browsed by deer or rabbits and untroubled by pests or disease. Plant it in a bold drift at the pond’s margin for a sweep of early-summer blue.