While Calibrachoa and Petunias are closely related and often confused, they are distinct genera within the Solanaceae (nightshade) family. They share a common lineage but have diverged, leading to significant differences in their botanical characteristics and, consequently, their care requirements. Understanding these distinctions is key to successfully cultivating each plant.
The most fundamental difference lies in their genetics. Petunias belong to the genus Petunia. Calibrachoa was once grouped with Petunias but is now classified in its own genus, Calibrachoa. This reclassification is based on major differences in chromosome count and DNA structure. Petunias have 14 chromosomes, while Calibrachoa have 18. This genetic divergence is the root cause of their differing physical traits and growth habits.
Visually, several key features set them apart. Calibrachoa, commonly known as "Million Bells," produces a profusion of smaller, bell-shaped flowers that are typically about 1 inch in diameter. Their foliage is smaller, stickier, and more slender. The plant itself has a more compact, trailing, and mounding habit with woody stems at the base. In contrast, Petunia flowers are much larger, often trumpet-shaped, and can reach over 4 inches in diameter in grandiflora types. Petunia leaves are broader, larger, and fuzzy or hairy to the touch. Their growth habit can be more upright and spreading, though many modern varieties are also vigorous trailers.
These morphological differences directly translate to specific care needs.
Watering: Calibrachoa is notably less drought-tolerant than most Petunias. Its smaller root system and prolific flowering require consistent moisture. Allowing it to dry out completely can cause the plant to stop flowering and become difficult to revive. Petunias are generally more forgiving of occasional dry spells, though they certainly perform best with regular watering.
Fertilizing: Both are heavy feeders, but Calibrachoa is exceptionally demanding. Its non-stop production of hundreds of small flowers depletes soil nutrients rapidly. It requires a consistent feeding schedule with a balanced, water-soluble fertilizer, often as frequently as weekly, or the use of a continuous-release fertilizer at planting. Petunias also benefit from regular feeding but are slightly less demanding.
Deadheading and Maintenance: This is a major practical difference for the gardener. Modern Petunias, especially the multiflora and milliflora types, are largely self-cleaning. However, the large-flowered grandiflora types often require regular deadheading (removing spent blooms) to prevent them from becoming soggy and moldy, which can lead to rot. Calibrachoa is completely self-cleaning; the spent flowers drop off on their own, requiring no deadheading to maintain its pristine, floriferous appearance.
