All three types—Grandiflora, Multiflora, and Milliflora—are cultivated varieties (cultivars) of the common garden petunia, which is a hybrid species known scientifically as Petunia × hybrida. This species originated from crosses between several wild Petunia species native to South America. The distinctions between these groups are not taxonomic but rather horticultural, bred specifically for differences in flower size, abundance, and growth habit to suit various gardening needs and aesthetic preferences.
Grandiflora petunias are characterized by their exceptionally large, showy flowers, which can measure up to 5 inches (over 12 cm) in diameter. These blooms are often ruffled or fringed, creating a dramatic visual impact in containers, hanging baskets, and garden beds. From a plant physiology perspective, the plant directs a significant amount of energy into producing these few, massive flowers. This often comes at a cost: the large, tender blooms are more susceptible to damage from heavy rain and wind. The plants themselves tend to have a more sprawling or mounding habit but may require more maintenance, such as deadheading, to encourage continuous blooming and prevent the plant from becoming leggy.
In contrast, Multiflora petunias produce a much greater abundance of flowers, but each individual bloom is smaller, typically measuring 1 to 2 inches in diameter. The plant's energy is distributed to create a prolific number of blooms rather than focusing on the size of each one. This results in a plant that is literally covered in color. From a adaptive standpoint, this trait is highly beneficial as the smaller, sturdier flowers are much more resilient to adverse weather conditions like rain and heat. They require less deadheading than Grandiflora types to maintain their appearance and will often continue to bloom profusely even without meticulous care, making them a more robust choice for mass plantings and landscapes.
Milliflora petunias are the smallest of the three types, representing a distinct dwarf growth habit. The plants are compact and mounding, typically reaching only 6 to 8 inches in both height and spread. Their flowers are proportionally tiny, usually about 1 inch across. Despite their miniature size, they are incredibly prolific bloomers, covering the small plant in a continuous blanket of color. This compact form is ideal for the front of borders, edging, and small containers. The plant's small scale means it has minimal resource requirements and is exceptionally self-cleaning, meaning spent flowers drop off naturally without requiring deadheading.
The primary differences lie in their floral display strategy and environmental tolerance. Grandifloras are the "showstoppers" with massive but fewer, more fragile flowers. Multifloras are the "workhorses," prioritizing quantity and durability over sheer size, making them better for season-long performance in variable climates. Millifloras offer a "miniature" option, with the highest flower-to-foliage ratio on the smallest possible plant frame. Their growth habits also differ; Grandifloras are often more vigorous and trailing, while Multifloras are generally more compact and bushy, and Millifloras are definitively dwarf and mounding.
