Petunias often reseed in the garden, but will not return true to type. They usually revert to a mix of small white, lavender and rose flowers. Aphids may become a problem. Slugs feed on petunias and can be controlled by the use of baits. Avoid wetting the foliage and flowers when watering to help prevent disease.
Petal blight can be a problem in rainy and very humid weather.
Viruses occasionally affect petunias. The types of petunias best suited to growing in South Carolina are the multifloras, millifloras and spreading petunias. Grandiflora petunias generally do not thrive in South Carolina because their large heavy blossoms are prone to damage and rot during hot, humid summers. Grandifloras have large flowers that are often frilled or ruffled along the edges. If you grow most grandiflora petunias, be aware that they will need extra care to look their best.