Petunias are annual flowers that blossom in the spring until the first frost in the fall. Petunias grow in flowerbeds and pots and range in a wide variety of colors. Deadheading a petunia extends the time that the flowers will grow blooms. It will also increase the number of blossoms on the plant, so that it looks healthier, and removing the dead and dying blossoms will prevent seed maturation.
Examine the petunias weekly after they produce flowers. Find flowers that appear to wilt and stems that do not contain petals because they have dropped. The stems may already contain seedpods.
Hold onto each stem below the spent flower. Pinch the flower head off the plant or use pruning shears to cut them off at a 45-degree angle. You can add the spent flower head to a compost pile or discard it in the trash.
Remove spent blooms as they appear throughout the growing season.
Cut the entire plant back when it appears leggy and overgrown. Cut the top 3 to 5 inches of the petunia off with garden shears.