Jennifer Schultz Nelson
Extension Educator, Horticulture
If it ever stops raining long enough to get in my garden, one of the plants sitting on my driveway patiently waiting to be planted is Calibrachoa, also called Million Bells. Up until a few years ago, I didn't really use this plant in my annual beds and containers. But the more I use it, the more I love it.
Calibrachoa, like Petunia, is a genus in the Solanaceae family. This is the same family as both deadly nightshade and tomatoes. Originally, Calibrachoa were considered to be part of the genus Petunia. After all, they do look like tiny petunias.
There has been a lot of debate in the botany world about whether Calibrachoa is its own separate genus or not. Modern DNA marker analysis, like what we see on TV shows like CSI, has supported the hypothesis that Calibrachoa are their own genus. Research published in 2005 looked at DNA fingerprints of all known species of Petunia and Calibrachoa and statistically measured how much of that fingerprint was shared among species. Their results showed Calibrachoa as a separate group from Petunia, suggesting that Calibrachoa is a separate genus.
Calibrachoa is native to South America, just like its cousin Petunia. In its native land Calibrachoa is considered to be a weak evergreen perennial. It can survive winters in hardiness Zones of about 8 or 9. In many parts of the world, central Illinois included, Calibrachoa is grown as an annual.
Europeans were introduced to Calibrachoa about 200 years ago, but they didn't start to reach their potential until a Japanese company called Suntory started experimenting with hybridizing them in the late 1980's. The first hybrid cultivars came on the gardening scene in the early 1990's. Nearly all of the Calibrachoa available in stores today are hybrid cultivars, most from Suntory.
I had never heard of this company before writing this article, but some internet searches revealed they are breeders of many different annual bedding plants. Their plants dominate the market in Europe. They also hold many patents on their hybrids.
Penn State University has tested hundreds of Calibrachoa hybrids in the field, and found that breeders are making real improvements in more compact plants, season-long flowering, flower color, size, and form. Another very important trait Penn State highlights is that the newer cultivars are more resistant to root rots, which can be a problem in Calibrachoa. Their observations suggest it may be worth your while to try the newest Calibrachoa cultivars available.
Calibrachoa plants look for all practical purposes like a petunia plant in miniature. Their leaves are pubescent (hairy) and flowers are trumpet shaped, about one inch in diameter. The flowers range in color from red to pink, magenta to blue. What I find unique is there are a lot of bronze, orange and yellow cultivars, colors you just don't see very often in Petunia. I've seen a few yellow Petunias, but not orange and bronze ones.
The growth habit of Calibrachoa varies. I love them in hanging baskets. They are great "spillers" cascading over the sides of a pot. Some cultivars are more upright and spreading, reaching a height of ten to fifteen inches, while others are more trailing or sprawling, and only reach of height of four to six inches.
A sunny spot in the garden is best for Calibrachoa. The more partial the sunlight, the less flowers they produce. They will flower best in a sunny location with periodic applications of fertilizer through the growing season. They also do best in acid soil less than a pH of 6.0.
Make sure where ever you plant Calibrachoa has well-drained soil. They do not like wet feet, and may have a tendency to develop root rot. The good news is they do tolerate drought well, so hot dry summers in Illinois shouldn't be a problem. Do keep a careful watch on plants in containers though, as containers can dry out way too much even for drought tolerant plants in our summer heat.
You may wonder, like I have, why all the Calibrachoas in stores are more expensive than the average Petunia. I've never seen them sold in flats, but always in three or four inch pots at a premium price. According to the Missouri Botanic Garden, Calibrachoa produces very little seed, making it impractical for producers to propagate them by seed. Instead, they are propagated vegetatively by cuttings from existing plants, which takes more time. This translates to a higher cost to the consumer.
Even though they do command a higher price, I have been using Calibrachoa more and more in my garden each year. The plants produce tons of flowers—you get a lot of bang for your buck. I use them primarily in containers, though this year I may put a couple in the ground just to see how they do. If you haven't tried Calibrachoa, I highly suggest you grow at least one this year. My bet is by the end of summer you'll be wishing you planted more.