Petunias bloom profusely from late spring until frost, making them a favorite bedding or container plant. The trumpet-shaped flowers range from miniature 1½ to 2 inches to giant 4-inch blooms and sport an array of colors. Often grown in hanging baskets or window boxes, trailing or vining varieties reach lengths of six feet or more when provided with adequate water, nutrients and sunlight.
Water petunias deeply to saturate the soil to a depth of 6 inches once a week, if grown in the flower bed. Container-grown petunias require more frequent watering and may need water as often as once a day. Frequently check the condition of the soil for moisture. Petunias suffer quickly without water, developing dry, curled leaves and reduced blooms.
Provide at least six hours of direct sunlight a day. Petunias thrive in sunlight and prefer all-day sun. Although they grow in partial shade, blooming size and number will be reduced without adequate sunlight. Plants that grow leggy and cease blooming typically require more sun.
Cut back petunias that suffer from excessive drying or that have grown leggy to revive the plants and spur new growth. Remove any dead or dried foliage and trim away shoots with reduced foliage or blooms. Water thoroughly and place in direct sunlight. Keep the soil moist.
Pinch back the terminal ends of branches when new growth reaches of 4 to 6 inches high to encourage dense, compact growth. This delays the flush of new blooms, but increases overall blooms.
Apply water-soluble fertilizer designed for flowers every 14 days to mounding or miniature petunias. Trailing or cascading petunias require weekly fertilizer to maintain their rapid growth.
Deadhead blooms as soon as they fade and do not allow flowers to go to seed. Setting seed halts the blooming process. Regular deadheading, sometimes as often as once a day, encourages the plant to produce new blooms. Petunias labeled as "self-cleaning" do not require deadheading.