Single grandifloras produce large blooms up to 5 inches across. Some single varieties have ruffled or fringed petals. Others possess a trailing habit which makes them ideal for window boxes and hanging baskets. Double grandifloras produce double, fringed flowers and are best suited to containers. Also, the flowers don't hold up as well during rainy weather.
Plants often become unkempt and straggly by late summer.
While the flowers on the multiflora petunias are smaller than the grandifloras, they produce many more flowers. There are both single and double flowered multiflora petunias. Multifloras are generally more compact and resistant to wet weather than the grandifloras. Single multifloras are excellent in mass plantings in flower beds. Double multifloras are most suitable for containers.