University of Vermont
Department of Plant and Soil Science

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CALIBRACHOA—ANNUAL FLOWER OF THE YEAR

Dr. Leonard Perry, Horticulture Professor Emeritus
University of Vermont
  
Each year the National Garden Bureau (ngb.org/year-of) names plants of the year, with the annual flower (lives only one year) for 2018 being calibrachoa (cal-eh-brah-CO-ah).  Although I’ve had mixed success with this group of flowers— and there are many to choose from in many colors— they’re commonly seen in garden stores in spring, and particularly in hanging baskets and containers.

It is sometimes seen as Million Bells, although this is a registered brand name of one of the early introductions of this flower.  Or, you may see this called “trailing petunia” from its small, petunia-type flowers.  But it is not a petunia, although related to them and in the same nightshade (Solanaceae) family.

Calibrachoa originally comes from the same part of South America as petunias— from southern Brazil to Peru and Chile— where it is an evergreen, sprawling and short-lived perennial. In this country it is only perennial in USDA hardiness zone 9 and warmer—along the Gulf coast, central Florida, and coastal California.  It was named for the 19th-century Mexican botanist Antonio de la Cal y Bracho. Breeders have crossed petunias with calibrachoa to form a hybrid genus (Petchoa).

Calibrachoa has a less dense habit, much smaller plant overall, and smaller leaves and flowers than petunias. It generally grows three to nine inches tall and up to 20 inches wide.  Since it has a very open habit, weeds are prone to grow among stems if you don’t use a weed fabric and mulch under plant stems.

Grow calibrachoa as you would petunias, in at least six to eight hours of direct sun a day.  It will tolerate less, but won’t bloom as well.  Growing soil should have a neutral pH around 7.0 —neither too acidic nor alkaline.  Their original habitats are cliff edges and rocky scree. 

Plant in a well-drained soil, and allow soil to dry between watering plants (obviously a problem in rainy weather). Established plants will tolerate drought, but repeated drying out makes plants more woody and less vigorous.  Overly wet soils often result in root rot diseases.

Fertilize regularly, according to label directions on product of your choice. It likes lots of nitrogen.  Calibrachoa is a low-maintenance plant, as it really attracts no significant pests or diseases. Their main growth problems may come from improper soils and watering, making them more suitable often for containers than ground beds and garden soils.  Cool soils during a cool northern summer may affect their ability to absorb certain nutrients like iron.

There is one series that you can grow from seeds—Kabloom— with the rest of the many varieties only available for sale as plants grown from cuttings.  If you want to try starting these seeds, they prefer a soil temperature of around 70 degrees (F).  It takes 10 to 14 days for germination, and eight to ten weeks to grow plants large enough to plant outside. 

There are many registered brands you may find for sale with names such as Million Bells, Superbells, MiniFamous, and Callie.  They come in many bright colors and combinations of colors with streaks, stripes, and star patterns.  There is a much wider range of colors than you’ll find with petunias.  Some flowers have dark “eyes” in the center of flowers, while others have bright yellow centers.  Some colors deepen with cooler temperatures, or fade with hotter temperatures.  If you don’t buy a container or hanging basket with plants already fully mature, combine transplants with other flowers to fill in around them and to spill over the pot sides.   

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