Grandiflora have large flowers (4 inches (10 cm)), and a large array of colors. Petunia Grandiflora supertunia by beautifulcataya. Multiflora has flowers of about 2 inches (5 cm). These are more tolerant than Petunia Grandiflora, and not as susceptible to damage from heavy rains or bright sunlight. They are often grown as an hanging basket plant.