Calibrachoa, commonly known as Million Bells, is a popular choice for gardeners seeking continuous color in hanging baskets and patio containers. The plant produces a cascade of small, trumpet-shaped blooms that resemble miniature petunias, lasting from spring until the first hard frost. While genetically a tender perennial, Calibrachoa is overwhelmingly cultivated and treated as an annual in most temperate regions.
Understanding Calibrachoa’s True Classification
The confusion surrounding the life cycle of Calibrachoa stems from its botanical classification as a tender perennial. Unlike a true perennial that survives freezing temperatures by going dormant, Calibrachoa is highly sensitive to frost. Although it has the genetic programming to live for more than one season, its native South American environment lacks severe winter cold.
Calibrachoa is only considered a perennial where winter temperatures remain consistently mild, specifically in USDA Hardiness Zones 9 through 11. In these warm regions, the plant can persist year-round. However, in Zones 8 and colder, the winter climate is fatal. This cold intolerance forces gardeners to treat the plant as a seasonal annual, replanting it each spring.
Strategies for Overwintering Calibrachoa
Gardeners outside of the warmest zones can preserve their plants by bringing them indoors before the first frost. The goal is to induce a period of semi-dormancy, not continued blooming. Before relocating, prune the foliage dramatically, cutting the stems back to two to four inches above the soil line. This trim reduces moisture loss and minimizes hiding places for pests like aphids and spider mites.
The container must be placed in a cool, bright location, ideally maintaining temperatures between 45 and 55 degrees Fahrenheit. This chill signals the plant to rest. During this dormant phase, watering should be drastically reduced, providing moisture only when the top few inches of soil are dry. Fertilization must be completely stopped until new growth resumes in the spring.
An alternative is to propagate new plants from cuttings taken in late summer or early fall. Take three to six-inch stem cuttings from healthy, non-flowering tips. Root the cuttings in a well-draining soil mix and keep them in a warm, brightly lit area indoors. These small plants require less space and are easier to manage through the winter than a large, mature container plant.
Essential Growing Care During the Season
Calibrachoa requires substantial sunlight to fuel its continuous production of blooms. The plant performs best when it receives a minimum of six hours of direct sun daily. In regions with extremely high temperatures, providing afternoon shade can help prevent wilting and stress.
Since they are grown in containers, Calibrachoa need consistent and deep watering, sometimes twice a day during hot weather. The potting mix must be well-draining, as the plant is highly susceptible to root rot if the soil remains soggy.
Calibrachoa are heavy feeders due to their prolific flowering nature. They benefit from a slow-release granular fertilizer mixed into the soil at planting. This should be supplemented with a water-soluble liquid feed every one to four weeks throughout the growing season. The plant is naturally self-cleaning, so deadheading is unnecessary. However, pinching back leggy stems encourages a denser, more rounded shape.