Until I started looking into it I thought that acanthus was better known as the inspiration for a widespread architectural ornamentation (see related post elsewhere) than it was as an actual plant. Not so. Acanthus mollis, in particular, but also other members of the genus are quite popular garden plants in USDA Hardiness Zones warmer than 7 and numerous on-line testimonials show that it can persist in Zone 6 and even 5.
I was probably a teenager when it was either pointed out to me or I realized that the folded areas at the tops of Corinthian columns represented vegetation. We may have learned this as a tangential part of my Latin classes. (Mrs. Savoit regularly used the class as a way to edify us generally. We were very parochial.) Forty-five years later I finally decided to find out what the entire plant looked like and was astonished to discover that it sported three stalks (technically, racemes) of bi-colored bilaterally symmetrical flowers shaded by darker hoods. Not only were the leaves impressive, the flowers were stunning.
Acanthus means “thorny” and mollis means “soft.” The leaves of this plant are tipped with spines that some describe as something to watch out for while handling, in spite of the trivial name. The leaves tend to be large and deep green with regular invaginations something like the leaves of red oaks. They spring up from ground level in a robust whorl and the flower stalks rise elegantly from their center.
The many gardening websites that allow readers’ comments are filled with praise and criticism of Acanthus. On the balance the comments are positive, but Californians, in particular, find that the plant is chronically invasive and hard to eradicate when it gets established. Because it will regrow from the smallest root fragment, the soil has to be removed down to 18 inches below the surface to definite rid your beds of the species.
In regions where the plant is less hardy it is reported to be much less annoying. Its impressive flowers are long-lasting (weeks, apparently) and give a welcome vertical component to garden designs. It begins to flower in the late spring, but in the U.S Southeast the entire plant may die back in the summer, succumbing to the heat and humidity.
One comment from Ithaca, N.Y. (USDA Zone 5b) noted that the flowers could be harvested at the height of their bloom and hung upside-down to be dried. This writer said that in their dried state they were attractive for up to a year, and that if hung at an angle, assumed “interesting shapes.” It is also recommended as an attractive cut flower.
The blooms of A. mollis have white bases that may shade outward into a purple or pink blush. They resemble snapdragons (Antirrhinum) or turtlehead (Chelone), but are more compressed and there is greater contrast in the colors of the “hoods” versus the flower’s petals. The flowers of A. balcanicus (native to the Balkan region) are more tightly clustered on the stalk than those of other species.
A. spinosus has spinier, more deeply cut leaves than A. mollis, causing them to resemble those of thistles. The flowers, however, are quite similar in the two species, as are the soil, sun, and temperature requirements.
The several members of the genus are native to the Mediterranean region, particularly North Africa and southern Europe, and as such tolerates drought well. In fact, some experts recommend it for xeriscaping. It will grow in almost any soil except those that are overly moist, and will tolerate full sun to part shade.
The common name in the US for Acanthus mollis is “bear’s breeches.” I could not find any origin story for this name. My impressionistic guess was “Bears are tough so they have thorny britches”? In Greece the vernacular name translates as “wild rhubarb,” evidently in reference to the similarity of the leaves and grow habit, and in Australia it is called “the oyster plant,” which likely refers to the white, flattened flowers. In Germany it is called bärenklau or “hogweed.”