Petunias have long been among the most popular annuals, thanks to their profuse bloom, incredible color range, and relative ease of culture. Plants are bushy to spreading, with thick, broad leaves that are slightly sticky to the touch. Flowers vary from funnel-shaped single blooms to densely double, heavily ruffled ones (like carnations); bloom sizes range from 1–6 in. across. They come in white and every color except green—from deep jewel tones to soft pastels. Bicolors and picotees are also available, as are types that have contrasting veins on the petals and kinds with fluted or fringed edges. In most climate zones, plants bloom throughout summer until frost. In Zones 12 and 13, summer heat kills them; in these areas, grow them for winter and spring color.
Petunias have traditionally been categorized as Grandiflora (large flowers on a bouquet-shaped plant), Multiflora (more numerous, medium-size blooms on a compact, mounding plant), or Milliflora (profuse small blooms on small, mounding plants). Trailing and mounding petunias were developed to grow as low as 6 in. and as wide as 6 ft. across. These categories are rarely used now, as advances in breeding have blurred the boundaries between them. New series and varieties appear each year in such numbers that no book could keep up. Check catalog descriptions and visit your local nursery to find the color, bloom size, and plant habit best suited to your purposes.
For a popular petunia relative with smaller blooms, see Calibrachoa. See also x Petchoa, an intergeneric hybrid between Petunia and Calibrachoa.
Plants thrive in rich, well-drained garden soil. Space them 8–18 in. apart, depending on plant size. After plants are established, pinch back halfway to encourage compact growth. Feed most kinds monthly with a complete liquid fertilizer; hungry trailing petunias—referred to by growers as the teenage boys of the plant world—do best when given controlled-release fertilizer at planting time in addition to weekly applications of liquid fertilizer. Near the end of the main bloom period, cut back rangy plants by half to force new growth.
In humid weather, botrytis disease can damage blossoms and foliage of most petunias. Smog damage (spotting on seedling leaves) and geranium (tobacco) budworm (flowers look tattered or fail to open) may cause problems in some areas.
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