Petunias for the Patio, Porch, and Garden Plot

Contact: Dr. Leonard Perry, Extension Professor
University of Vermont

The petunia is among the most popular bedding plants purchased each spring and summer, In fact, some people may argue that it is the most popular. If you drive around Vermont in the warmer weather, it certainly may seem like this is so.

This favorite annual flower was first discovered in South America more than two centuries ago. The earliest petunias were small-flowered and lanky and were found in only two colors, white and purple. But even as early as the beginning of the nineteenth century, European breeders were experimenting with crossbreeding to develop larger flowers and more colors.

Today, petunias are available in shades of white, yellow, pink, blue, purple, and red as well as bicolors, and as single or double flowers. Many have a light, sweet fragrance, especially the blue petunia varieties. Petunias make excellent cut flowers and will last for four to six days.

Petunias are members of the Solanaceae or nightshade family, which includes tomatoes, peppers, and Salpiglossis (which the early petunias closely resembled). They are suitable for hanging baskets, containers, and window boxes, and as edges for flowerbeds or to add color to vegetable gardens.

Most gardeners buy bedding plants, but you could grow your own petunias from seed. Sow seed indoors eight to 12 weeks before the average last-frost date in your area. Double-flowered varieties may require more time to bloom, so start them at least 12 weeks before transplanting time.

When buying bedding plants, look for plants with healthy foliage and plenty of buds. There should be no signs of dried out or spotted leaves or powdery mildew.

For container planting, use a soil-less mix. If you're planting petunias in the ground, choose a location with light, rich soil and good drainage. (Petunias will grow in almost any kind of soil but do best in this soil.) Work in some peat moss or compost before planting. Mulch to help keep down weeds and retain soil moisture.

Petunias like full sun (at least six hours a day) but will do fine in partial shade. However, in part shade the plants will flower less and the stems will stretch more.

These summer annuals are drought-tolerant, so don't worry about watering unless there are prolonged periods of drought. Window boxes and containers, especially those located under overhanging eaves, should be checked every few days, however, and watered as needed as the soil tends to dry out more.

Petunias require little care but will benefit from a monthly dose of fertilizer. Double-flowered cultivars will flourish from biweekly fertilizing.

By midsummer, your petunias may have stretched out stems and fewer flowers. Prune them back severely to encourage new shoots and flowers to develop. Don't cut back trailing petunias.

Source: UVM Extension