Soft petals and an exquisite fragrance make petunias a natural choice for the garden. Whether you plant them in containers or in the ground, petunias will grace your outdoor spaces from springtime until the first frost. Wait until the soil warms to 60 degrees Fahrenheit (15.5 degrees Celsius) before you transplant petunias into your garden. There are hundreds of varieties that are categorized based on size and growth habit. Good drainage is more important than rich soil when it comes to maintaining your petunias' health. This plant needs a minimum of five solid hours of sun each day, as ample light is the single most important factor affecting how well it grows. Remember to remove faded flowers by deadheading, or pinching or cutting off the flower, to encourage more blooms and help the whole plant stay healthy and fresh.