Million Bells, scientifically known as Calibrachoa (commonly Calibrachoa x hybrida), belongs to the Solanaceae family, which includes petunias, tomatoes, and nightshades. The genus Calibrachoa comprises about 28 species of evergreen, short-lived perennials and subshrubs, often grown as annuals.
Named after 19th-century Mexican botanist Antonio de la Cal y Bracho, Calibrachoa was once classified as a petunia but was distinguished as a separate genus in 1985 due to chromosomal and morphological differences. Most cultivated varieties are complex hybrids, derived from South American species, and are patented, prohibiting commercial vegetative propagation.
Calibrachoa plants are compact, mounding, or trailing, typically growing 6–12 inches tall and spreading up to 24 inches wide. Their small, oval-shaped leaves are sticky, fleshy, and bright green, measuring about 1 inch long. The trumpet-shaped flowers, resembling miniature petunias, are 1 inch in diameter and bloom profusely from spring to frost in a rainbow of colors, including pink, red, yellow, orange, purple, and white, often with stripes, speckles, or double blooms. The flowers are self-cleaning, dropping spent blooms without needing deadheading. Stems are semi-woody, and the plant has a sprawling habit, ideal for cascading over edges.
Native to South America, particularly southern Brazil, Peru, Chile, and parts of Mexico, Calibrachoa species grow naturally in scrub, open grasslands, and rocky coastal areas. In their native habitats, they form low, carpet-like growth in well-drained, sunny environments and can self-seed. Introduced to global markets in the early 1990s, Calibrachoa hybrids are now widely cultivated as ornamentals in temperate and tropical regions, including North America, Europe, and Australia. They are popular in urban and residential gardens but are not typically naturalized outside their native range due to low seed production in hybrids.
Calibrachoa is winter hardy as a perennial in USDA Zones 9–11, where it can survive mild winters with temperatures above 25°F (-4°C). In colder climates (Zones 2–8), it is grown as an annual, as it cannot tolerate frost or prolonged cold. In Zones 9–11, plants may be overwintered indoors in bright, cool conditions (50–60°F) or protected outdoors with mulch. For annual use, plant in spring after the last frost when soil temperatures reach 55–60°F. Its heat and mild drought tolerance make it suitable for warm-season gardens, though it may need shade in extreme heat.
Calibrachoa is primarily an ornamental plant, valued for its vibrant, continuous blooms and versatility in landscaping. Its trailing habit makes it ideal for hanging baskets, window boxes, containers, and as a ground cover or “spiller” in mixed planters, adding color to patios, balconies, or garden beds.
The flowers attract hummingbirds, bees, and butterflies, enhancing pollinator-friendly gardens, though double-flowered varieties are less accessible to insects. It serves as a companion plant with petunias or lantana, complementing their similar needs. While not edible, its low-maintenance, self-cleaning nature and deer resistance make it a favorite for gardeners seeking vibrant, hassle-free displays.
Cultivation of Million Bells
Select a Sunny Location
Choose a site with full sun, providing 6–8 hours of direct sunlight daily to maximize flowering and maintain compact growth. In hot climates (e.g., Zones 9–11 summers), partial afternoon shade prevents scorching. Ensure space for its trailing habit, typically 6–12 inches tall and spreading up to 24 inches, ideal for cascading over edges.
Use Well-Drained, Fertile Soil
Plant in well-drained, slightly acidic to neutral soil (pH 5.5–6.5) enriched with organic matter like compost or peat moss. A commercial potting mix with perlite or vermiculite is ideal for containers, ensuring good drainage to prevent root rot. Avoid heavy clay soils; amend garden beds with sand or compost if needed.
Plant at the Right Time
Plant nursery-grown Calibrachoa in spring after the last frost when soil temperatures reach 55–60°F, typically April to May in most zones. Space plants 8–12 inches apart in beds or 6–8 inches in containers to allow spreading. For Zones 9–11, fall planting is viable for winter blooms in frost-free areas.
Water Consistently
Keep soil evenly moist but not waterlogged, watering when the top inch feels dry, about 1–2 times weekly depending on climate. Containers may need daily watering in hot weather. Use a watering can or drip irrigation to target the root zone, avoiding wet foliage to prevent fungal issues. Reduce watering in cooler months.
Mulch for Containers or Beds
Apply a thin (1-inch) layer of organic mulch, such as bark or pine straw, around plants in garden beds to retain moisture and suppress weeds, keeping it away from stems. In containers, a light layer of decorative gravel enhances drainage and aesthetics. Mulch helps regulate soil temperature, especially in fluctuating spring or summer conditions.
Fertilize Regularly
Feed every 1–2 weeks during the growing season with a water-soluble, balanced fertilizer (e.g., 20-20-20) or one high in phosphorus (e.g., 10-30-20) to boost flowering, diluted to half strength. Alternatively, apply a slow-release granular fertilizer at planting. Avoid over-fertilizing, which causes leggy growth; reduce feeding in late fall for perennials.
Pinch for Bushier Growth
Pinch back stem tips by 1–2 inches early in the season (4–6 weeks after planting) to encourage branching and a fuller, bushier habit. No deadheading is needed, as Calibrachoa is self-cleaning, dropping spent blooms naturally. Mid-season trimming by one-third can rejuvenate leggy plants, promoting new blooms.
Monitor for Pests
Watch for aphids, spider mites, or whiteflies, which may appear in hot, dry conditions. Check for sticky residue, webbing, or yellowing leaves. Treat with a strong water spray, insecticidal soap, or neem oil, applying early morning or evening to avoid leaf burn. Encourage beneficial insects like ladybugs to control pests organically.
Prevent Fungal Diseases
Calibrachoa is prone to root rot or powdery mildew in overly wet or humid conditions. Ensure proper drainage, space plants for air circulation (8–12 inches apart), and water at the base. Remove affected leaves and apply a fungicide if mildew appears. Avoid overhead watering and improve ventilation in dense plantings.
Support Pollinators
The vibrant flowers attract hummingbirds, bees, and butterflies, enhancing garden biodiversity. Plant with salvia, lantana, or petunias to create a pollinator-friendly display. Avoid pesticides during blooming to protect beneficial insects, especially for single-flowered varieties, which are more accessible than double blooms.
Propagate with Cuttings
Propagate via stem cuttings in late summer for overwintering or new plants, as most Calibrachoa hybrids are patented and seed propagation is unreliable. Take 3–4-inch cuttings, remove lower leaves, dip in rooting hormone, and plant in a moist perlite-peat mix. Rooting takes 2–3 weeks under bright, indirect light at 70°F.
Overwinter in Cold Climates
In Zones 2–8, treat as an annual or overwinter indoors in a bright, cool location (50–60°F) with reduced watering. Cut back by half before moving indoors. In Zones 9–11, mulch heavily and cover during rare frosts to protect perennials. Alternatively, take cuttings in fall to propagate new plants for spring.
Choose Vibrant Cultivars
Select nursery plants from series like ‘MiniFamous’, ‘Superbells’, or ‘Cabaret’ for diverse colors (orange, yellow, pink) and growth habits (mounding or trailing). Check for healthy, compact plants with no yellowing leaves. Pair with complementary plants like verbena or bacopa in mixed containers for a cohesive, colorful display.
Additional Tips
- Container Growing: Use pots (10–14 inches wide) with drainage holes, filled with a lightweight potting mix, for patios or balconies. Ensure pots allow cascading growth for maximum effect.
- Heat Management: In extreme heat, move containers to partial shade or mist plants to prevent wilting, especially in Zones 9–11 summers.
- Long-Term Care: Replace plants every 1–2 years in perennial zones, as Calibrachoa weakens over time. Refresh soil annually in containers to maintain vigor.