Gardening Articles: Flowers :: Annuals
All About Petunias (page 4 of 4)
by Peter Kopcinski
Throughout most of the country, petunias are warm-season flowers that can produce a carpet of color from spring until frost. In intermediate- and low-desert areas such as Tucson and Phoenix, and in eastern zone 10, petunias fail in humidity or during extended periods of high heat (temperatures in the 90s), or both. In those regions, grow them as winter annuals, planting in fall and enjoying them through late spring.
Plant in full sun in rich, well-drained soil. If your soil is either very sandy or clayey, amend it by incorporating about 6 cubic feet of composted organic matter per 100 square feet.
Plant grandiflora and multiflora types about 10 inches apart, and Wave and Surfinia types 2-1/2 to 3 feet apart. After plants are established, pinch back halfway for compact growth. For optimum growth, feed monthly with complete liquid fertilizer. If you live in long-season zones 7 or 8, cut back plants halfway in August to force new growth.
Trailing petunias also need sun and well-drained soil, but they need more nitrogen fertilizer than bedding petunias because of their more rapid growth. An iron chelate spray or a nitrogen fertilizer with extra iron will promote attractive dark green leaves.
Pests. In humid weather, gray mold (botrytis) damages flowers and leaves of most types. There's no practical remedy if you live in a wet-summer climate beyond planting resistant types, such as multifloras. The ozone in smog causes silvery spotting on leaves (petunias are so sensitive that they are good indicators of invisible ozone pollution). Tobacco budworm is a problem in some areas. Snails and slugs dine on petunias as well as other plants, and likewise, aphids may gather on succulent new stems.
Peter Kopcinski is a seedsman living in Marlton, New Jersey.
Photos by Suzanne DeJohn/National Gardening Association.