The answer: When it’s called Supertunia, Million Bells, Superbells, or Calibrachoa (pronounced kal-u-bru-koa). They’re part of a group I refer to as designer annuals. They’re more expensive than flats of familiar annuals since they’re usually patented and often available only in larger pots.
Which means that if you need a dozen or more to use as bedding plants, they'll be costly. But, despite the price tag, these plants can be useful in the garden. They do have qualities gardeners may feel are worth paying more for.
The problem is, most of us know what to expect from a “regular” petunia but not a petunia look-alike such as a Calibrachoa. So it may be difficult to decide if they’re really worth the extra money.
We started seeing these plants in the 1990s, and they’ve become very popular for their low-growing, trailing growth habit.
They’re also heat-tolerant, keep blooming until cold weather, and – why I grow them -- don’t need the old blossoms picked off. I can’t think of anything duller than deadheading petunias all summer!
In general, these are full-sun plants, perfect for hanging baskets, window boxes, and other containers. They need good drainage. Many will attract hummingbirds, which is a plus.
My experience with this group of plants has been positive. I like them, but am not overwhelmed with enthusiasm. I’m not sure why. Still, my “garden” is mostly made up of large containers, so these “designer petunias” are useful. And each year I find myself picking up one or more pots of them.
This year I’ve planted ‘Cabaret Yellow’ Calibrachoa, which is being called trailing petunia. Like some of the others mentioned, it has smaller flowers than traditional petunias. (Think of them as minipetunias.)
But what draws me to this plant is that the yellow of the flowers is a much brighter, clearer color than I’ve ever been able to find in petunias – and I like that very much.
I’ll report later on how it performs. And I'd be interested in hearing others’ experiences with this group of plants.