Sun perennials are plants that need about six hours of direct sunlight daily—and most thrive in the afternoon sun. Some of the most popular sun perennial plants are irises, peonies, coneflowers, daisies, lilies, daylilies and many ornamental grasses. Many other sun perennials are available, and it's easy to find plants to fit into your sun-filled garden spaces. Most gardeners like to plant a variety of sun perennials with varying bloom times so that colorful flowers are blooming from spring to the first fall frost. When buying sun perennials, some factors to consider are their grow zone, light requirements, soil requirements, mature height and spread, bloom time, foliage and color, and other qualities such as fragrance, drought tolerance and deer resistance.