Blue Wave Petunia Seeds (Ground Cover Type). The original Waves are still the best seed-raised trailing petunias. They require no pinching and a single plant can spread to 1.5 m (4′) across and will hug the ground at only 15 cm (6') tall. Although described as a "ground cover", Wave Petunias will not tolerate foot traffic. Colourful purple-plue 5-7.5 cm (2-3") wide blooms smother the plants.