Petunias originally hail from South America but can now be found growing across North America. The University of Vermont calls them one of the most popularly grown annual flowers for the spring and summer. Provide petunias with the correct growing environment and conditions they need to thrive, and add lush color to your landscape for many months.
Choose a growing site. For the healthiest growth, select a garden area that receives a minimum of five hours of direct sunlight per day, according to the University of Minnesota.
Amend the soil. Petunias can grow in relatively poor soil but will respond well to the addition of organic material. The University of Minnesota recommends mixing in 3 inches of organic matter, like aged compost.
Plant the petunias in the ground. Whether you're sowing seeds or planting transplants, space the petunias 12 inches apart, according to Iowa State University. For best results, wait until the soil temperate is a minimum of 60 degrees F, according to the University of Rhode Island.
Fertilize the petunias after they've been planted. Use a standard 10-10-10 or 5-10-5 garden fertilizer, applied at the rate listed on its bag. Make a second fertilization application three months after planting, at half the recommended rate. This provides the flowers with an extra nutrient boost to encourage continued blossom production, but don't fertilize more than this. Excess fertilization can cause a drop in flower production, according to the University of Rhode Island.
Water the petunias. Petunias grown in the ground should be watered once a week, according to Iowa State University. Apply enough water to soak the soil to a depth of 6 to 8 inches.
Trim off wilted, old blossoms to encourage healthy blossom production. Use a pair of pruning shears or sharp scissors to snip off the old flowers.