According to the University of Maryland, hummingbirds find Lobelia cardinalis, or cardinal flower, and Lobelia siphilitica, or great blue lobelia, attractive. They can usually grow together in a garden.
Cardinal flower has a deep red color and grows best in partial shade because full sun could fade the color. The flowers grow along long stalks and take turns opening, starting from the bottom of the stalks. This extends its bloom season, providing hummingbirds with nectar for a long period of time.
True to its name, great blue lobelia has blue flowers. It blooms a little later than cardinal flowers and grows to reach a slightly shorter mature height.