Wildly Successful: Acanthus mollis

In the fifth century BC, a Greek artist carved elegant leaves in the stone capitol at the top of a column, using a species of Acanthus as the model. His design became popular as the Corinthian style of column; if you peer up at neoclassical columns on buildings in modern cities, you may still see acanthus leaves at the top. The plants themselves are not always as honored in our gardens, often popping up in odd corners, seemingly unappreciated and untended. But when acanthus is healthy and well placed, it is a strikingly elegant plant.

Acanthus mollis is native to rocky woodlands across southern Europe, from Portugal to Italy, Sicily, the former Yugoslavia, and northwestern Africa. The plants we see in our gardens are mostly A. mollis var. latifolius, a native of Spain and Portugal with leaves reaching two feet across on stems four feet tall; the stately flower stalks average five to six feet tall.

Acanthus makes a bold statement in a small space and can be splendid in larger spaces with other strongly architectural plants—as witness, the planting of acanthus with tree ferns across the street from the Conservatory in San Francisco’s Golden Gate Park. The plant is likely to overrun other small plants grown with it, except for similarly aggressive plants such as Bergenia crassifolia or Nephrolepis cordifolia.

Acanthus flowers are pollinated by large insects (mainly bumblebees) that are able to force apart the two pairs of sturdy stamens to reach the nectar at their bases. Gardeners often think of the crooked stamens as little frogs inside the flowers. Each flower has four sepals and one spiny bract, all flushed soft purple, and a tubular corolla with a three-lobed lower lip. Though not brightly colored, stems of acanthus flowers are formally handsome. They last well in bouquets and, if cut before the bottom flower fades, preserve well for use in dried arrangements.

Acanthus is at its best in part shade where summers are hot, but full sun is fine in cool summer areas. It will also survive in deep shade, but may flower little there. The plant generally survives in Northern California gardens with no care, dying back in summer, regrowing in fall. It will look better if grown in fertile soil, and leaves will stay green through summer if the soil is kept moist; plants may be more vigorous if their leaves are cut back at summer’s end. Check the plants frequently for slugs and snails and use iron phosphate bait if they are numerous.

Acanthus clumps enlarge slowly. They can be divided by cutting off sections of rootstock with visible leaf buds in fall or spring. They can also be grown from root cuttings taken in late fall or early winter; plant three-inch long root sections vertically in a cutting mix. To germinate ripe acanthus seeds, soak them in water for a day or two, plant them one-quarter-inch deep in a seed mix, and grow at 50-55°F. They typically sprout in twenty-one to twenty-five days. Seedlings will take two or more years to reach flowering size.

Acanthus seeds form in capsules that split open when ripe, expelling the seeds to some distance. It is best to cut off the flower stems before the capsules can ripen to prevent seeding all around the mother plants. Where acanthus meets a lawn, mowing will stop its spread. To confine it most certainly, plant it in a bed that is bounded by concrete or confine it using an eight-inch deep root barrier, such as one would use for bamboo. The ability of acanthus to grow from small sections of root means that the plant is difficult to eradicate should you wish to grow something else in its place. While it can be done, total removal requires deep digging, and sprouts may have to be removed for two or three successive seasons. Under no circumstance should you rototill the area, as this will only increase the number of root fragments from which new plants can grow.

Varieties and Similar Species

Acanthus mollis has leaves only eight inches across and of a duller green than those of A. mollis var. latifolius. A common cultivar, ‘Hollard’s Gold’ (syn. ‘Fielding’s Gold’ and ‘New Zealand Gold’), has broad, golden green leaves.

Several other species of Acanthus can be found by the adventurous gardener. Easy to locate and an excellent garden plant, Acanthus spinosus (usually available as A. spinosus var. spinosissimus) has flower stems to about four feet tall, and narrower, more divided leaves than A. mollis. It grows best in full sun. Some gardeners feel its attractiveness and restrained size more than make up for the rather sharply pointed leaf spines. Because this species is native to the area where the first Corinthian columns were carved, some think it might have been the model, though both species were grown in ancient Greek gardens.

Acanthus (uh-can’-thus) derives from the Greek word akantha, which means thorn or prickle; mollis (moll’-liss) means soft. While a number of acanthus species are rather prickly, the thorniest part of A. mollis is the bract under each flower. It has several moderately firm points and is probably the source of the common name, bear’s breeches. We call it that without thinking much about what part of the plant a bear might wear, but it seems likely that the original name referred to the sharply pointed bracts, which were seen as little bear paws with claws on them. “Breeches” seems to originate with a mishearing of a Medieval Latin name, branca ursina, which meant bear’s claw. Medieval French gardeners may have misheard branca as braca, a word that later became braies and finally breeches.

Adapted from Wildly Successful Plants for Northern California Gardens, by Pam Peirce with photographs by David Goldberg, to be published by Sasquatch Books in January 2004.