Wave petunia plants have a spreading growth habit, with the ability to fill flower beds and containers with their blooms that sprout all along their stems, which can reach up to 4 feet. These plants want to grow and thrive, and seem to increase on a daily basis. Plant them in full sun in moist, well-drained soil. Keep the soil moist, but never soggy. Feed them with an all-purpose fertilizer when you first plant them, and every two weeks after that until the middle of summer.