Petunias have been one of the most popular flowering annuals for years. Their popularity can be attributed to several desirable traits. Petunias are easy to grow, bloom reliably all summer, and are available in a wide range of colors, flower forms, and growth habits.
Petunia varieties can be divided into two main groups based on flower and growth habits. The two types are grandifloras and multifloras.
Grandifloras are large-flowered petunias consisting of both single and double flowering forms. Single grandifloras produce large blooms up to 5 inches across. Some single varieties have ruffled or fringed petals. Others possess a trailing habit which makes them ideal for window boxes and hanging baskets. Double grandifloras produce double, fringed flowers and are best suited to containers. Generally, grandifloras (single and double) don't flower as heavily as multifloras. Also, the flowers don't hold up as well during rainy weather. Plants often become unkempt and straggly by late summer.
While the flowers on the multiflora petunias are smaller than the grandifloras, they produce many more flowers. There are both single and double flowered multiflora petunias. Multifloras are generally more compact and resistant to wet weather than the grandifloras. Single multifloras are excellent in mass plantings in flower beds. Double multifloras are most suitable for containers.
Some petunia varieties are categorized as floribundas. These are actually modern multiflora petunias. The modern multifloras possess slightly larger flowers and are more compact than older multiflora varieties. Some of the modern multifloras include the Madness, Carpet, Polo, and Celebrity Series. (A series is a group of closely related varieties with uniform characteristics, such as height, spread, and flowering habit. Generally, the only characteristic which varies within a series is flower color.)
A new type of low, spreading petunia is represented by the variety 'Purple Wave.' 'Purple Wave' is a 1995 All-America Selection. Plants grow only 4 to 6 inches high, but can spread 2 to 4 feet. The burgundy-purple flowers measure 2 inches across. 'Purple Wave' is an excellent choice for hanging baskets and as an annual groundcover.
Petunias are easy to grow if a few requirements are met. Petunias perform best in a sunny location. They also require a moderately fertile, well-drained soil. Adequate soil fertility can be maintained by working a complete fertilizer, such as a 5- 10-5, into the soil each spring. Use about 2 to 3 pounds per 100 square feet of planting space. Soil drainage can be improved by incorporating organic matter (compost, peat, or well-rotted manure) into the upper 6 to 8 inches of soil.
When buying petunias in the spring, select compact, stocky plants. Tall, spindly plants take considerably longer to recover from transplanting. Once purchased, harden the plants outdoors for a few days before planting them into the garden. Initially place plants in a shady, protected area and then gradually expose them to direct sun. Bring them indoors at night if freezing temperature are predicted. Petunias can be transplanted into the garden after the danger of frost has passed. In central Iowa, the last frost usually occurs around May 5-10. Plant petunias about 12 inches apart. Pinch back the plants to encourage branching. Pinching is especially helpful for tall, leggy plants.
This article originally appeared in the April 14, 1995 issue, p. 44.