A Gardening Journal
Today in the Garden of a Lifetime: Porto Spineless Cardoon
- Published: November 02 2016
The extraordinary size and silvery-blue color of the leaves of cardoons—let alone their fountain-like array that's sometimes as large as the canopy of a palm—make them irresistible. Plus, plants can succeed spectacularly both as annuals and perennials.
I've always grown this architectural beauty directly in the garden. The straight species of cardoon is a monster—OK, a space hog—so when I had opportunity to grow the more compact Porto Spineless form, I jumped at it. And, for once, why not in a container? Then, I could move the entire plant into the greenhouse for the winter, so I didn't have to do the "extreme" mulching I detail in the How To of the original post. On the other hand, yes, then I would need to schlep the containered cardoon to the greenhouse this month, and back to the garden in May.
Container growing has several advantages. Cynara cardunculus is a sunlover, and I can position and even reposition a containered cardoon to receive the maximum throughout the season. Cardoons growing in-ground in mature beds such as mine—packed with ever- burgeoning plants—are likely to become partly shaded by high Summer as this or that exuberant neighbor becomes even larger than the cardoon.
Below, my container of a first-year Porto Spineless cardoon. This cultivar is reported to be more compact than the straight species. Certainly when growing in a seven-gallon container, it's one third the size of a first-year plant of the species. But the big news is the "spineless" in the cultivar name. The leaves' thick petioles lack the small but tediously sharp spines that make the straight species a comparative pain to handle. (Porto is a city in Portugal, perhaps the cultivar was identified there?) Porto Spineless is favored by floral growers—cardoon ranchers, as it were—who might be faced with a field of hundreds of plants, not just one or two used as garden specimens.
In the above photo, sitting on the courtyard gravel awaiting transport back to the greenhouse, the containered cardoon is in marvelous adjacency to the red-pink-burgundy leaves that the oakleaf hydrangea sports in the fall. The dense, tiny leaves of the line of dwarf box provide another surefire contrast. There's no room for a cardoon in this bed, nor for a containered one to sit on the gravel all season either. But for a couple of weeks in the fall, this is a great trio.
Cardoon foliage doesn't change color in cool or even cold weather; if temperatures remain above twenty degrees Fahrenheit or so, the plant stays evergreen or, rather, "eversilver." If your climate and siting cooperate to enable a plant to perennialize without winter protection, its silvery size and texture are a gift year-round. On the other hand, that same persistence above-ground regardless of the weather is probably the reason Cynara cardunculus isn't reliably hardy in climates colder than Zone 7.
The climate where I garden is just a bit colder than Zone 7, which makes it the easier and more fool-proof choice to grow cardoon as an annual. I try to stock my clients' gardens with the fool-proof choices, but for my own, I make the interesting ones. Here I've grown cardoons as both annuals and perennials, whether in the ground or in a container.
Here's how to grow cardoons as annuals, perennials, and—now—container specimens kept active year after year.