Grandiflora petunias are characterized by their exceptionally large, showy flowers, which can reach diameters of 4 to 5 inches. From a botanical perspective, this cultivar group has been selectively bred to prioritize massive bloom size over sheer quantity. The flowers are often single, featuring a classic trumpet shape with a wide, flared mouth, though many modern varieties also exhibit stunning double or fringed (fimbriated) forms. The substantial size of the blooms makes them highly susceptible to damage from rain and wind. The thin, delicate petal tissue can become easily bruised, waterlogged, and torn, which can lead to a ragged appearance after inclement weather. Consequently, Grandiflora types often perform best in protected environments like containers on covered patios or hanging baskets under eaves where they are shielded from the elements.
Multiflora petunias present a distinct contrast, defined by a significantly higher number of flowers that are individually smaller, typically measuring 1.5 to 3 inches across. The plant's energy is directed toward producing a prolific abundance of blooms rather than enlarging each individual one. Botanically, this results in a denser, more floriferous plant that creates a solid blanket of color. A key physiological advantage of Multiflora petunias is their greater resilience. The smaller, sturdier flowers and somewhat thicker pedicels (flower stalks) are more resistant to breakage and are less prone to damage from rain. This makes them a superior choice for in-ground garden beds and exposed planters where they must endure natural weather conditions. Their growth habit is generally more compact and mounding, allowing them to maintain a tidier appearance throughout the growing season with less maintenance.
Milliflora petunias represent the smallest category in terms of both plant size and flower dimensions. These are true miniature petunias, with blooms that are typically only 1 to 1.5 inches in diameter. The plants themselves are petite, compact, and well-branched, forming dense mounds that are completely covered in tiny, intricate flowers. From a horticultural standpoint, their miniature scale is a product of selective breeding for specific dwarf genetics. Despite their small size, the flowers are perfectly formed replicas of their larger relatives. This compact growth habit and continuous blooming nature make them ideal for the front of borders, for edging pathways, or for planting in small containers and window boxes where a delicate, refined texture is desired. They are highly weather-tolerant and often self-cleaning, meaning they do not require deadheading to continue blooming profusely.
