Gardening Articles: Flowers :: Annuals
All About Petunias (page 2 of 4)
by Peter Kopcinski
Kinds of petunias
Most modern petunias descend from two wild species from Argentina, a large white one (P. axillaris) and a violet-flowered one (P. integrifolia, formerly P. violacea). The initial hybrids of these two were produced in Germany and England in the early 1800s. Over time, they proved so stable--not to mention popular--that botanists now refer to them simply as P. hybrida.
This nearly 200 years of gene mixing combined with petunias' great popularity (and the modern habit of giving plants a trademarked name) has led to some confusion among types.
When planning a petunia color scheme, keep in mind that purple-flowered varieties tend to be the most vigorous, while yellow ones--except for 'Prism Sunshine'--are the least. Red-flowered varieties of all types also tend to be weak. The breeding required to produce yellow and red varieties results in genetically weaker plants than the naturally hardy purple ones.
Following are descriptions of the basic petunia hybrids, with listings of strains that I've found to be superior.
Grandiflora. Of all petunias, these produce the fewest but largest flowers, 3 to 5 inches across. Since their introduction in the 1930s, they've been the most popular type of petunia.
Plants grow 1 to 2 feet high and 2 to 3 feet wide. The flowers can be single, ruffled, or fringed. Colors include blue, pink, red, rose, salmon, scarlet, white, and pale yellow, plus striped forms of these colors. Double flowers are also available.
Grandifloras are damaged by rain and strong winds. Also, the plants' thick, heavy stems have a tendency to fall over, resulting in unsightly holes in the planting. It may be difficult to find a place in the garden protected enough to show off grandifloras' full splendor all season. I like to grow them in a cutting bed and let the flowers take a starring role in arrangements.
Among the grandifloras, the big news is 'Prism Sunshine'. This 1998 All-America winner is notable for both its bright yellow color and its vigorous growth. (Earlier yellow petunias produced weak plants of modest performance.)
Multiflora. Sometimes called floribundas, multiflora plants are similar in size to grandifloras, but their flowers are only about 2 inches in diameter. Their chief virtue is more abundant flowers that have greater resistance to disease and bad weather. Because their branching is denser, they are less likely than grandifloras to flop over. They are also available in more colors than any other kind of petunia. Overall, they make neat, compact plants that cover themselves in bloom.
Despite their many virtues, multifloras are less vigorous than other petunias and not really suited to center stage in the garden.
Milliflora. These dwarf petunias grow to about two-thirds the size of multifloras. Small, delicate, 1- to 1-1/2-inch blooms cover the compact plants, which are ideal for containers, window boxes, and hanging baskets. I plant millifloras as a border, spacing them about 8 inches apart. Plants form mounds 6 to 8 inches across. Don't expect them to fill into a solid mass like other petunias. To show off the compact, dense mounds, plant them in clusters of three, five, or seven, depending on space. Space plants about 9 inches apart.
In the southern states (USDA Hardiness Zones 7 and warmer), millifloras are hailed as a long-lasting new bedding plant that won't flop over. In zones 5 and cooler, some critics have noted a relative lack of vigor. My experience is different. I have enjoyed them for the last three years in Vineland, Ontario (zone 5), and find that when planted early and given good care, they are very welcome additions to the garden.
Unlike the multitude of series and varieties common to other petunias, only one type of milliflora is available: the Fantasy series, offered in nine colors.
Doubles. Grandifloras, multifloras, and some trailing types are available with double flowers. All of these novelties, but especially the trailers, are striking in mass plantings. My preference is to place them in beds or planters where you can see them at close range and appreciate the blooms' complexity. While most double-flowered petunias are available as seed for home gardeners, seeds of doubles have less vigor so take longer to germinate and grow.
The Doubloon strain includes a solid pink as well as a veined pink, blue, and lilac. The more upright-growing Marco Polo, bred in Australia, comes in four clear colors: blue, rose, white, and a very showy pink. Both Doubloon and Marco Polo petunias are marketed under the Flower Fields brand.