The delicate little flowers of the plant with a major name belie its hardy nature. Although it looks somewhat fragile, Calibrachoa, or observation petunias (Calibrachoa x hybrida), is prized for its ability to withstand hot, dry conditions and for its constant flowering habit that continues till the first frost. Hardy at U.S. Department of Agriculture plant hardiness zones 9 through 11, Calibrachoa plants vary in height from 3 to 15 inches, based on the particular hybrid and cultivar.
Short Cultivars
Million Bells is a trademarked hybrid group that has numerous cultivars. One of the shorter ones is known as “Trailing Blue .” This plant features dense masses of little blue flowers and reaches an average maximum height of between 3 and 8 inches. Another cultivar from the Million Bells group, “Trailing Red,” might only be one of the smallest cultivars available of all the hybrids. This cultivar, which attracts hummingbirds and butterflies, reaches a maximum average height of just 1, two or three inches.
Medium Cultivars
Medium-sized cultivars of the these two large hybrid classes tend to average between 6 and 10 inches in their maximum heights. “Yellow Calibrachoa,” that is part of the Million Bells group, features cheerful, lemon-yellow blooms and is an upright cultivar rather than trailing. “Double Ruby,” that is part of the Superbells group, characteristics heavily-ruffled blossoms in a bright pink hue. This cultivar’s branches will trail upon the floor or over the edges of a container.
Tall Cultivars
Superbells “Spicy Calibrachoa” is one of the tallest of the Superbell hybrids. This plant, that features brilliant, orange-red flowers with bright yellow borders, reaches an average height of between 8 and 12 inches. A Million Bells cultivar, “Tropical Delight,” can also be about the tall side, with an average maximum height between 9 and 12 inches. This plant contains a mounded growing habit.
Care Tips
Calibrachoa will not achieve its maximum height if it isn’t supplied with optimum environmental problems. Tender perennials, the plants do not tolerate frost very well and are often grown as annuals. Calibrachoa prefers full sunlight and conditions on the dry side. In actuality, Calibrachoa cannot tolerate wet soil. The plants tend toward developing root rot and should only be planted where the soil drains well. For this reason, Calibrachoa specimens are occasionally grown in containers that have holes at the base to permit for good drainage. They must also be given plenty of sunshine, as well as shade will limit development and flowering.
Suggested Uses
In hanging baskets, window boxes or other containers, Calibrachoa’s long stems rubbed down magnificently. The plants may also be effectively used as a ground cover in small areas, in rock gardens and at border fronts. Calibroachoa plants aren’t usually bothered by insect pests or diseases, according to the Missouri Botanical Garden, and they do not need any deadheading to produce continuous flowers. For all these reasons, they’re an excellent choice for starting home gardeners or young children.