Petunia

Purchase transplants or start seeds indoors ten to twelve weeks before the last frost date. Petunia seeds are extremely fine and need light to germinate, so press them onto the surface of moist seed-starting mix without covering. Maintain consistent moisture and a temperature of 70 to 75 degrees Fahrenheit for germination in seven to ten days. Transplant hardened-off seedlings outdoors after all danger of frost has passed.

Plant in full sun in well-drained, fertile soil or high-quality potting mix for containers. Space plants twelve inches apart in beds or use three to five plants per twelve-inch hanging basket. Petunias are heavy feeders, especially in containers, and benefit from liquid fertilizer every seven to fourteen days throughout the growing season.

By midsummer, many petunia varieties become leggy and sparse. Rejuvenate them by cutting stems back by half, which stimulates a vigorous flush of new growth and flowers within two weeks. Deadhead spent blooms regularly on grandiflora types, though many modern spreading varieties are self-cleaning. Water at the base when possible, as wet foliage and heavy rain can damage large-flowered types.

Petunias are native to South America, with wild species found primarily in Argentina, Brazil, Uruguay, Paraguay, and Bolivia. The genus Petunia contains approximately 20 recognized wild species that grow in a variety of habitats ranging from coastal dunes to subtropical grasslands and rocky outcrops. The first petunia species collected by European botanists was Petunia axillaris, a white-flowered, sweetly fragrant species discovered in Argentina and Uruguay in the early 1800s. Shortly afterward, Petunia integrifolia, a smaller purple-flowered species, was collected from southern Brazil. Both species were sent to European botanical gardens, where breeders quickly recognized their ornamental potential. By the 1830s and 1840s, European horticulturists had begun crossing these two species, producing the first hybrid petunias that displayed a remarkable range of colors and flower forms far exceeding what either parent species could offer. The resulting Petunia x hybrida became one of the most commercially important bedding plants in the world. Throughout the 20th century, intensive breeding programs in the United States, Japan, and Europe produced thousands of cultivars organized into distinct classes: Grandiflora types with large individual blooms, Multiflora types with abundant smaller flowers and superior weather tolerance, Milliflora types with compact growth and miniature blooms, and the groundbreaking spreading or Wave types introduced in the 1990s that could cover large areas without pinching. The introduction of vegetatively propagated varieties like Supertunia and Surfinia further expanded the palette of available colors, patterns, and growth habits while improving garden performance.

Petunias thrive in fertile, well-drained soil with a pH of 6.0 to 7.0. In containers, use a premium potting mix with good drainage and moisture retention. Feed container petunias weekly with a water-soluble balanced fertilizer at half strength, or every two weeks at full strength. In-ground petunias benefit from a slow-release granular fertilizer worked into the soil at planting and supplemental liquid feeding monthly. Iron deficiency causes yellowing leaves and is corrected with chelated iron applications.

Petunias are primarily garden display flowers rather than cut flowers, as individual blooms are short-lived in arrangements. However, small bouquets can be made by cutting stems in the morning with several buds about to open. Deadhead regularly by pinching off spent blooms and their developing seed pods to redirect energy into new flower production. For seed saving, allow a few flowers to develop seed pods and collect when they turn brown and begin to split open.

Fresh petunia stems last only two to three days in a vase, making them impractical as cut flowers. Their beauty is best enjoyed in the garden or container. Petunia flowers can be pressed between parchment paper for botanical crafts, retaining their color reasonably well. Trailing petunia varieties can be brought indoors before frost, cut back, and grown as houseplants on a sunny windowsill through winter, then returned outdoors the following spring.