|This is one of few perennials that has fall color with narrow green leaves, glaucus underneath, turning yellow. Light blue, star-shaped flowers in open panicles are present from May through June. Requires very little care in moist, fertile soils. A wonderful border plant. When using this plant in flower arrangements, sear end. Take care, as sap is poisonous and may cause irritation on contact. Grows to 2 feet tall and 18 inches wide. The American Horticulture Society ranks this as one of their top 75 great plants for the garden.