Wave petunias trail attractively from long stems with blossoms along their full length, making these annual flowers ideal choices for hanging baskets and window boxes. While wave petunias do not require deadheading (removal of spent blossoms), gardeners may want to promote bushier growth and more attractive growth by cutting back scraggly stems or thinning the center.
Monitor the growth of the wave petunias so you can cut them back when they become overgrown or when the blooms begin to decrease. Overgrown wave petunias have long, thin stems with smaller and fewer blossoms.
Trim every third trailing stem by one-third to one-half of its length to create bushier growth. Some gardeners pinch off the tender stems with the index fingernail and thumbnail. Other gardeners prefer to use pruning shears and use a straight cut. Either method works because the stalks are tender and easily broken. The stems can be pruned at any point along the stem. While appearing quite bare after trimming, wave petunias will recover within one to two weeks.
Perform intermediate pruning (pruning for shape) on a weekly basis by examining under the blossoms at the very end of the stems. Often under these blossoms form tiny new stems that will grow into long stems, leading to an unbalanced and overgrown petunia plant. Pinch these tiny new stems at the larger stem with your fingernail and thumbnail.
Open a crowded and overgrown center of a wave petunia to allow adequate sunlight and air into the plant's interior by pinching back or using the shears. This pruning does not need to be drastic--remove the top third of several stems that cross each other or wrap around the center.
Use the stems you remove in a cut floral arrangement. Remove the foliage and blossoms from the bottom half of the stems and place the stem in a vase filled with cold water.