Sporting silvery-white blooms with dark purple centers, Tidal Wave Silver is distinct. Unlike other petunias, gardeners can decide the height of the mature plant. Tidal Wave Petunias can attain heights of 2 to 3 feet if spaced closely together, about 6 inches, and given support such as a trellis. If plants are spaced a foot apart, the mounded, hedge-like plants will reach 16 to 22 inches. Neither pinching nor pruning is needed for flowers all season.