When I look at the Acanthus plants in my garden, I think of the TV detective, Adrian Monk, and how he described his amazing analytical skill: “It’s a gift…and a curse.”
That phrase also neatly captures the spirit of the Acanthus.
The Acanthus genus includes 30 species that are native mostly to the Mediterranean Basin, with some in Asia. The species that are most often found in gardens are A. balcanicus (a smaller variety), A. mollis (spineless), and A. spinosus (deeply cut leaves with spiny margins
As a gift to the garden, the Acanthus forms a clump 3-4 feet high with arching, glossy-green leaves 2-3 feet long. (The shape of the A. mollis leaf inspired the design of the capital of the Corinthian column, which was used extensively in Greco-Roman and Classical architecture.)
In the late spring the plant generates spikes of white flowers that resemble snapdragon blossoms, and that are hooded by spiny, reddish-purple bracts. The flower spikes rise well above the leaves, and last into mid-summer.
The plant grows reliably in sun or shade, looks attractive year-round, and is maintained easily with annual trimming of flower spikes and leaves as they fade. It might need protection from snails and slugs, but my plants seem untroubled by those pests.
Then, there’s the Curse of the Acanthus, which has two parts. The first part is its invasiveness, which takes the form of creeping rootstocks that generate new plants in an ever-widening area that extends in all directions from the mother plant.
The offsets can be separated at the roots for easy propagation, if you should want another gardener to share your burden with this garden thug.
The second part of the Curse appears after removal of an unwelcome Acanthus from the garden: if the tiniest piece of the plant remains in the ground, it will shrug off the insult of removal and spring into vigorous new life.
Still, this plant could become an asset in the garden by controlling its invasiveness. It might be grown in a large container or a bed that is isolated by masonry surroundings. For example, it is being grown in concrete tree wells on Pacific Avenue in Santa Cruz.
For an Acanthus planted in the ground, the gardener might achieve control by installing a rhizome barrier, a thick rubbery material that is sold by the foot in yard-wide sheets. This is used most often to control running bamboo but should also be effective in keeping an Acanthus plant within preferred boundaries. The Acanthus’ roots are relatively shallow, so an 8-inch deep root barrier should do the job.
I now have length of rhizome barrier that I will cut into strips 12 inches wide and install to corral my Acanthus spinosus. It’s a plant worth keeping…and hard to eradicate.
As an unrelated note, I will share one of Adrian Monk’s classic remarks: “If I had a nickel for every time someone said, ‘You need professional help for your OCD,’ I’d have $2,796.45.”
Tom Karwin is past president of Friends of the UC Santa Cruz Arboretum, Monterey Bay Area Cactus & Succulent Society, and Monterey Bay Iris Society, and a Lifetime UC Master Gardener (Certified 1999–2009). Visit ongardening.com for previous columns. Send comments or questions to gardening@karwin.com.
