Petunias are tender perennials grown as annuals in many parts of the U.S. According to the Alabama Cooperative Extension Services, this versatile plant has consistently remained in the top five purchased bedding plants by U.S. gardeners for more than 100 years. With more than 400 cultivars, petunias are available in nearly any color and bloom profusely from late spring until fall. Wave and trailing varieties create cascades of color when grown in hanging baskets, making them ideal for hanging from the deck or front porch to welcome visitors to the home.
Prepare a sunny location for petunias that receives six to eight hours of direct sunlight a day. Till the soil to a depth of 6 to 8 inches. Remove rocks, roots or other debris and rake smooth.
Test the soil to determine the pH level and nutrients in the soil. Follow the directions in the kit to balance nutrients and adjust the pH to 5.5 to 6.2.
Spread a 2- to 3-inch layer of compost or well-rotted manure over the soil. Mix into the soil with a garden tiller or hoe. This improves the texture of the soil, promotes drainage and increases aeration.
Transplant petunias to the garden after all danger of frost has passed in your area. Space mounding petunias 12 inches apart. Spreading or trailing petunias require 2 to 2 1/2 feet between plants.
Pinch out new growth on the ends of branches or mounding petunias to encourage dense foliage. This forces the plant to send out new branches along the stem. Repeat this in 3 weeks by pinching out the ends of all branches.
Water petunias grown in the ground once a week. Saturate the soil to the root level. Petunias in hanging baskets or containers might require daily watering depending on the size of the plant, rate of growth and weather conditions. Keep the soil moist, but avoid soggy soil.
Fertilize with water-soluble fertilizer every 10 to 14 days throughout the summer.
Deadhead blooms as soon as they begin to fade. This tricks the plant into thinking it has not produced enough bloom to reproduce and results in increased blooms. Petunias labeled as "self cleaning" do not require deadheading.