Acanthus, a plant native to the Mediterranean region, is gaining attention for its resilience and decorative qualities in gardens across Napa County. The plant, known for its shiny dark green leaves and tall stature, provides visual interest during winter months when many other plants are dormant.
Cindy Watter, a UC Master Gardener of Napa County, shared her experiences with acanthus. “Acanthus is one of my favorite plants. Right now, when my yard is mostly dormant—except for camellias and wild onions—it is a pleasure to see the acanthus unfurling its shiny dark green leaves,” she said.
Watter noted that acanthus serves as an effective accent in landscaping due to its height and elegant appearance. It can complement various architectural styles from Victorian homes to midcentury modern residences. The plant’s historical significance dates back to the 5th century when Greek stone carvers used the leaf shape to decorate columns—a design still visible at landmarks such as the U.S. Capitol in Washington, D.C., the Palace of Fine Arts in San Francisco, and Churchill Manor in Napa.
The species Acanthus mollis var. latifolius is commonly found in local gardens. While some variants have prickly leaves—the name “acanthus” itself means prickly—this particular variety only has barbs beneath its flower bracts.
Pollination occurs through bumblebees that access nectar by pushing apart the sepals of lavender and white flowers shaped like foxgloves; unlike foxglove, however, acanthus is not toxic.
According to Watter, mature acanthus plants can reach four feet wide and tall, with summer flower spikes growing up to six feet high. She advises containing them within edged beds since they can spread aggressively if left unchecked. In hot climates, partial shade benefits their growth; minimal watering is required except during peak summer heat.
Pests such as slugs and snails may target acanthus but have not been problematic in Watter’s garden. For those using slug bait as a deterrent, she cautions pet owners to keep animals away from treated areas.
Propagation can be achieved by dividing clumps in fall or spring or planting root cuttings in soil-less mix until roots develop before transplanting outdoors. Seeds require soaking before sowing at 55°F; germination takes about three weeks but flowering may take two years.
To prevent unwanted spreading via seeds or root fragments—which are difficult to eradicate—gardeners should remove flowers before seed capsules form and avoid rototilling near established plants.
Maintenance includes cutting back faded foliage at summer’s end; new growth typically appears after winter rains. Mulching helps protect roots during cold spells while occasional compost or balanced organic fertilizer supports healthy development even in poor soils.
Watter observed that some gardeners replace acanthus with more water-dependent species like hydrangeas despite its low maintenance needs: “There’s a lot to like in a plant that is beautiful and doesn’t demand much care—or water.”
The UC Master Gardeners of Napa County will host a free virtual talk titled “Healthy Soil = Healthy Plants” on March 5 from 7 pm to 8 pm via Zoom for those interested in learning more about soil health issues affecting plant vitality. Registration details are available through the Napa County Library website.
Gardeners seeking advice can contact the Master Gardener Help Desk online or visit the University of California Cooperative Extension Office at 1710 Soscol Avenue, Suite 4, Napa on Mondays and Fridays between 10 am and 1 pm.
