Inviting Thistles into the Garden

Thistles are not welcome in most gardens. Bold, tall, and very spiny bull thistles are quite literally painful to remove. Canada thistles are prickly and very persistent, seeming to come back tenfold from every attempt to pull them.

There are, however, thistles that add beauty, form and even food to the garden.

Artichokes (Cynara cardunculus var. scolymus) are bold foliage plants with enormous thistle blooms that are harvested before they open. Like the familiar weed thistles, artichoke blooms are hidden in the center of a swollen base protected by thick green bracts that overlap like fish scales, crowned with a tuft with hundreds of rolled purple petals. The edible portions are the hearts and the ‘petals’ –soft flesh inside those thick bracts. The part that would unfold into a showy flower is inedible, the ‘choke’ that lies at the center below the heart.

By nature artichokes are biennials, flowering in the second year of life. Since they are not cold hardy to Michigan, typical forms are not suitable for our gardens. Hybrids such as Green Globe flower in their first year of life, and will produce edible crops for us.

An artichoke relative is cardoon (Cynara cardunculus), whose leaves are bold, coarse and silvery. New shoots are edible and have a flavor like, not surprisingly, an artichoke. More often, they are grown as an ornamental plant for their fabulous leaves. Though hardy only to USDA zone 7 (0 degrees F), I have had them survive a mild winter with good snow cover. The foliage is less of a neat fountain in the plant’s second year, but the flowers are quite dramatic.

A more common ornamental is the globe thistle, Echinops. Leaves resemble thistles, but are not so prickly. Blooms are perfectly round balls of silvery blue flowers; an interesting contrast to the otherwise coarse plants. They reach three to four feet tall, and bloom from July to September. Full sun is ideal but they will perform well in as few as six hours. Globe thistle is not fussy about soil type, deer and rabbits do not like the leaves, but butterflies adore the flowers.

An assortment of varieties offers flowers in shades of blue and a range of heights. Arctic Glow provides a unique variation, with silvery white flower globes and contrasting burgundy stems.

Sea holly, or Eryngium, offers a wide range of foliage forms and flowers for the garden. I have had the best success with Eryngium planum, whose rosette of rounded leaves is not so thistly. The flowers, however, are a dense dome of steel blue, resting on a spiny base. I have tried some of the species with bold, spiny, silver-netted leaves with flowers resting atop bracts as flashy as a poinsettia. So far the biennial types like Mrs. Wilmott’s Ghost have not flowered for me. More reserved species have failed to come back for that second, flowering season. But I will keep trying.

I have had good luck with another thistle that seems to be available mostly as seed. This is the Scotch thistle, Ondopordum acanthium. The flowers are typical thistles, small, and not so showy. Foliage, however, is very dramatic. Leaves are broad, flat and almost white. Stems are winged, with ridges of the same silvery white. Plants are tall, six to eight feet, and make a bold, architectural statement. Plants are biennial, with a distinctive rosette of silvery foliage in their first year, and a tall, blooming form in their second year of life. Seedlings are readily recognized, so it’s easy to keep just what you want from one year to the next.

Consider giving the showy thistles a chance in your garden.