'Purple Robe' Cup Flower: A Perfectly Behaved Edging Perennial

For a long-blooming, no-fuss edging plant, landscape designer Wes Brittenham recommends dwarf cup flower (Nierembergia caerulea 'Purple Robe'). "It flowers all summer, no deadheading needed," he says. Hardy in Sunset zones 8–24, it forms a neat 6- to 12-inch mound, isn't invasive, resists pests, and thrives on weekly watering. "As perfectly behaved as you could want."

Brittenham pairs it with fine-textured companions like red-flowered Salvia greggii, gaura, or pineleaf penstemon (P. pinifolius).