Petunias are one of America's favorite annuals, offering a long season of bloom in a huge array of colors and forms. The petunia's height can range from 4 to 18 inches, with a spread anywhere from 18 inches to 4 feet. They are often used to spectacular effect in civic gardens and plantings.
Petunia flower colors come in almost every shade, ranging from white to a deep purple, sometimes striped or edged with a second color or having contrasting veins. There are soft pastels of pink, yellow and lavender, and vivid bright shades of red, hot pink and purple. The trumpet-shaped flowers can be small (1 inch) or large (4 inches) and come in ruffled or double forms as well. Many are sweetly fragrant.
Grandifloras are the most popular petunias and have large, heavy flowers, often with ruffled or frilled edges. The flowers can be damaged by rain. Commonly seen varieties are Supercascade, Dream and Ultra.
Multifloras are more durable and free-flowering than grandifloras; they come in both single and double forms and are typically used in masses to provide a swathe of color. Celebrity, Primetime and Carpet are popular varieties.
Milliflora petunias have much smaller inch-wide flowers that grow in abundance and rarely require pruning back. They work well mixed with other plants in a container, or when used as an edging plant. The Fantasy series is a widely grown milliflora.
Trailing or spreading petunias are low-growing but cover up to 4 feet and flower all along the stems. The plants are vigorous, require little maintenance and are useful as a ground cover or in baskets. The first and best known of this form is the bright, rose-purple Purple Wave. The newer Tidal Wave petunias are similar but grow much taller, reaching to 16 to 22 inches. Avalanche and Ramblin are two other trailing varieties.
Petunias want full sunlight. If planted in too much shade, they will become spindly and produce fewer flowers. They prefer a light, well-drained soil.
If sowing petunias from seed, start the seeds 8 to 10 weeks before planting out. If buying nursery plants, look for short, compact plants. Often, petunias that have not set bloom will settle in faster than those that are already flowering. Pinching off the top inch of the plant will encourage it to branch. Plant outside after all danger of frost is past, gradually exposing plants to outdoor conditions.
Most types should be planted about 12 inches apart; the spreading types need more room and should be planted 2 feet apart.
Long, deep watering is preferable, since frequent light watering will encourage shallow rooting. Container plants may require watering as often as every day. Feed monthly with a balanced fertilizer. Petunias that become leggy can be encouraged to put out new growth by pinching back the shoots by half. Many of the smaller-flowered cultivars are self-cleaning, but larger forms and double flowers require dead-heading to maintain heavy bloom.
Petunias may reseed, but will not come true to type.
Since they bloom reliably all summer long, petunias are often planted in large masses to provide broad swathes of color. They are also useful in garden borders, containers and hanging baskets. The ground-cover types will quickly cover a slope.
Petunias are bothered by few pests or diseases. Control for slugs, if necessary. Keeping foliage dry when watering will help prevent mold and other diseases.