Calibrachoa, also known as million bells, is a popular flowering plant known for its small, petunia-like blooms that cascade from hanging baskets and containers. While these plants offer vibrant color, they are susceptible to common problems that can hinder their growth and flowering. Addressing these issues is key to successful cultivation.
Environmental and Cultural Problems
Calibrachoa often exhibits issues stemming from its growing environment or care. Problems like yellowing leaves or stunted growth often indicate improper watering, light, or nutrient conditions.
Watering Issues
Both too much and too little water severely impact Calibrachoa. Overwatering often leads to yellowing leaves, wilting despite wet soil, and can cause root rot, a fungal disease. The soil should be consistently moist but never soggy, as these plants are sensitive to overly wet conditions. Conversely, underwatering results in wilting, crispy leaves, and stunted growth. In containers, allow the top inch or two of soil to dry slightly before watering again.
Light Problems
Calibrachoa thrives in bright conditions, requiring at least six hours of direct sunlight daily for abundant flowering. Insufficient light leads to leggy, stretched growth with sparse blooms and pale leaves. While they can tolerate some partial shade, especially in hotter climates where afternoon shade can prevent stress, too much shade significantly reduces flower production. Conversely, excessive harsh direct sun, particularly in extreme heat, can cause scorched leaves and faded flowers.
Nutrient Deficiencies
Calibrachoa are “heavy feeders” and can quickly deplete soil nutrients, especially when grown in containers. A common issue is iron deficiency, manifesting as yellowing between the veins of new leaves, while older growth remains green. This often occurs when soil pH is too high (above 6.2), making iron unavailable. Overall pale growth can indicate a general nitrogen deficiency, particularly in older leaves, as the plant moves this mobile nutrient to support new growth. Regular fertilization with a balanced, water-soluble fertilizer every one to four weeks during the growing season prevents these deficiencies.
Temperature Stress
Calibrachoa prefers moderate temperatures, generally performing best between 60°F and 85°F. Extreme cold can lead to stunted growth, purplish discoloration of foliage, and leaf drop. While some hardened-off plants can tolerate a mild frost, they are typically grown as annuals in cooler climates due to their sensitivity to freezing temperatures. Excessive heat, especially temperatures exceeding 90°F, can cause wilting or reduced flowering. Providing afternoon shade during intense heat waves helps mitigate heat stress.
Pest Infestations
Calibrachoa can attract several common garden pests that weaken the plant and diminish its appearance.
Aphids: Small, soft-bodied insects that cluster on new growth, stems, and buds, feeding on plant sap. They cause leaves to yellow and curl and excrete honeydew, which can lead to sooty mold. Use a strong water spray, insecticidal soap, or neem oil.
Spider Mites: Tiny arachnids thriving in hot, dry conditions, causing stippling or bronzing on leaves, especially undersides. Increase humidity and apply insecticidal soap or neem oil.
Whiteflies: Small, white, winged insects that suck sap from leaves, leading to yellowing and wilting. Use sticky traps for monitoring and reduction, or apply insecticidal soap or neem oil.
Thrips: Slender insects that feed on flowers and leaves, causing distorted growth and silvery streaks. They are often most prevalent when blooms are forming.
Common Diseases
Calibrachoa can be susceptible to certain diseases, particularly when environmental conditions are unfavorable.
Powdery Mildew
Appears as a white, powdery substance on leaves, leading to leaf distortion and premature leaf drop. This fungal disease is favored by poor air circulation. Increase airflow and avoid overhead watering; fungicides may be necessary.
Botrytis Blight (Gray Mold)
Causes brown, water-soaked spots on leaves, flowers, and stems, developing into a fuzzy gray mold. Remove infected plant parts and improve air circulation.
Root Rot
A widespread issue linked to overwatering or poorly draining soil. Symptoms include yellowing leaves, wilting, stunted growth, and plant death as roots turn black and rot. Prevent root rot by using well-draining soil and avoiding prolonged saturation.
Preventative Care and Maintenance
Consistent preventative care and maintenance are fundamental to keeping Calibrachoa healthy.
Proper watering: Check soil moisture and allow the top layer to dry slightly before watering.
Adequate light: Ensure at least six hours of full sun daily for vigorous growth and abundant blooms.
Regular feeding: Use a balanced fertilizer for continuous flowering and overall plant health.
Good air circulation: Proper plant spacing helps prevent fungal diseases.
Pinching back: Occasionally pinch tips to encourage bushier growth and more blooms.