The National Garden Bureau has named calibrachoa the “Annual of the Year.” What are calibrachoas? You might be more familiar with their current popular name “million bells” or “mini-petunias” as they were originally marketed.
You would not have found calibrachoa in your grandmother’s garden because they did not hit the U.S. garden market until the late 1980s. Calibrachoa were not instantly popular with U.S. gardeners, but we were won over in the early 1990s when Japan’s Suntory Company introduced calibrachoa hybrids. These sweet flowers are native to Brazil and other parts of Latin America where they grow with limited soil along rocky cliff edges.
Home gardeners were initially disappointed with “mini-petunias” because they did not perform as well as garden petunias. They were very intolerant of wet, heavy or poorly drained soil. Calibrochoas may have looked like little petunias, but research into their DNA makeup revealed that calibrachoa are not small petunias. Instead, they are in a separate genus of their own in the Solanaceae or nightshade family alongside their cousins that include tomatoes, peppers, potatoes, petunias and nightshade.
I tried some of those early varieties of calibrachoa and never had much success. They were finicky about watering and they tended to grow long and straggly. Today’s varieties are much improved with a decreased proclivity to root rot, a more compact form, and bloom that lasts the entire season.
Today’s calibrochoa are definitely better performers than their predecessors, but they still insist on a very well-drained soil that is not kept constantly wet. They are both heat and drought tolerant and do their best in full sun. Use of a slow-release fertilizer at planting time followed up with regular applications of fertilizer will keep them blooming through the summer. Growers recommend using a fertilizer that provides them with adequate levels of both nitrogen and available iron because calibrachoa need higher levels of these two nutrients than most annual flowers.
Trailing calibrachoa may become a bit leggy and ragged by the middle of summer. If they do, simply trim them back a bit to tidy them up. This will result in bushier, more vigorous plants. While mid-summer rejuvenation trimming may be needed, calibrachoa are “self-cleaning,” meaning they do not require deadheading (the removal of spent flowers) to keep them blooming.
The first calibrachoa marketed to U.S. gardeners were more expensive than many annual flowers because they were patented hybrids that were propagated exclusively by cuttings. Seeds saved from these hybrids’ would not produce plants that looked exactly like the parent plants. This changed when the PanAmerican Seed company introduced the Kabloom series of calibrachoa in 2014.
The Kabloom series includes Deep Pink, Deep Blue, Red, White, and Yellow varieties. Kabloom plants are trailing and grow about 8 to 12 inches tall and 14 inches wide. Calibrachoa series from other seed companies include Superbells, MiniFamous, Cabaret, Callie, Million Bells, Cruze, Aloha Kona, Can-Can, Noa and Calipetite.
Whether propagated from cuttings or seeds, it is easy to see why calibrachoas with their millions of small, brightly colored petunia-like flowers have become so popular for use in hanging baskets and patio containers. Treat these flowers of the year right and they will reward you with season-long florific beauty.
Marianne C. Ophardt is a retired horticulturist for Washington State University Benton County Extension.