Flowers that are naturally blue include bellflowers, plumbago, morning glory, bugleweed, blue star, periwinkle, flax, Siberian squill, gentians and agapanthus. Hydrangeas that are grown in acidic soil produce blue flowers. Wildflowers that are blue include bluets, hepaticas, chicory, penstemons, vervains, bluecurls, blue toadflax, nemophilas and blue-eyed grass.
Flowers that are truly blue as opposed to lavender or purple are fairly rare. They tend to bloom in the early spring and summer, but those with flowers that persist into the late summer can balance out and contrast with the plants with red or yellow flowers that bloom later in the season.