The large, bright orange, fully double cactus flowers with twisty-turny petals of the Inca zinnia (Zinnia elegans 'Inca') make this cultivar a favorite to light up the fall garden bed. This upright, bushy annual also makes a great cut flower for bouquets. Inca zinnia grows to 3 feet tall with a 1- to 2-foot spread when grown in optimal conditions of hummus-rich, well-drained soil and in full sun.