Calibrachoa, widely known as Million Bells, are popular flowering plants that provide continuous blooms from spring until the first frost. Their prolific flowering and trailing habit make them a favorite for hanging baskets, containers, and garden beds. Maintaining appropriate temperature conditions is important for their sustained health and abundant blooming throughout the growing season.
Understanding Calibrachoa Temperature Preferences
Calibrachoa thrive within a specific temperature range. These plants generally prefer daytime temperatures between 55°F and 65°F (13°C to 18°C). This moderate range supports healthy vegetative growth and encourages the development of numerous flower buds.
Nighttime temperatures also play a role in their well-being. Maintaining temperatures within a similar moderate range, or slightly cooler than daytime, generally benefits plant health. This consistent environment allows calibrachoa to continue their metabolic processes efficiently, leading to continuous and vibrant blooms.
Calibrachoa and Cold Stress
Temperatures falling below the optimal range can induce cold stress in calibrachoa. Calibrachoa is sensitive to frost, with damage typically beginning when temperatures drop below 32°F (0°C). However, a hardened-off plant can tolerate a mild frost, potentially down to around 28°F (-2°C).
Symptoms of cold stress include wilting, stunted growth, and discoloration of leaves. Prolonged exposure to cold can lead to reduced flowering and, in severe cases, plant death. Even if the plant doesn’t immediately perish, its health and blooming can be significantly compromised.
Calibrachoa and Heat Stress
Conversely, temperatures rising above the preferred range harm calibrachoa. While generally considered heat-tolerant, heat stress can occur when temperatures exceed 90°F, becoming more severe above 95°F or 100°F. High temperatures can reduce the plant’s transpiration rate, affecting its growth.
Indications of heat stress include wilting, faded flower colors, and browning leaf edges. The plants may exhibit reduced vigor, and in extreme heat, they can enter a semi-dormant state, leading to a significant reduction or cessation of blooming. Consistent high heat and dry soil can further exacerbate stress on the plant.
Strategies for Temperature Management
Protecting calibrachoa from temperature extremes involves practical measures. For cold protection, container-grown plants can be moved indoors to a bright, cool location, ideally around 50-60°F (10-15°C), before the first frost. In garden beds, covering plants with frost cloths or clear plastic storage tubs overnight can provide insulation.
To mitigate heat stress, providing afternoon shade is beneficial, particularly during prolonged heatwaves or when temperatures exceed 90°F. Adequate and consistent watering is also important, as hot weather and wind can cause soil to dry out rapidly. Mulching around the base of the plants can help retain soil moisture and regulate soil temperature, reducing heat stress.