How to Plant, Grow, and Care For Acanthus
Acanthus brings bold, structural foliage and form to the shady border. Join gardening expert Katherine Rowe in exploring the handsome architectural perennial that thrives in partial sun and shady garden sites.
Contents
Acanthus is an architectural perennial with bold vertical interest and handsome, lush leaves. The scrolling foliage unfurls to form broad, frond-like leaves with a tropical look.
Distinctive bloom spikes emerge in early summer on tall stalks, densely lined with creamy white and purple flowers to steal the show. The lush, glossy specimens grow primarily for their ornamental leafy structure with the added benefit of the towering bloom spikes.
In the right situation, Acanthus grows easily with little maintenance and long-lasting display qualities.
Acanthus Overview
Plant Type
Herbaceous perennial
Family
Acanthaceae
Genus
Acanthus
Species
Acanthus spp.
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Native Area
Europe and Africa
Exposure
Partial shade
Height
3-5’
Watering Requirements
Average
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Pests & Diseases
Powdery mildew, slugs, and snails
Maintenance
Low
Soil Type
Average
Hardiness Zone
5-10
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What is Acanthus?
Acanthus, or bear’s breeches, comprises about 22 species from Europe, Asia, and Africa, with a long garden history. The architectural specimen has dark, glossy, deeply lobed leaves. The name is from the Greek “akantha,” meaning spines, in reference to the spiny leaf margins on some species.
The specimens appear as early as the fifth century in architecture and art. As a leaf motif in ancient Greek and Roman architecture, they adorn Corinthian column capitals. In Greek mythology, Akantha was a nymph who rebuffed the god Apollo’s romantic advances, for which he turned her into a thorny plant.
Acanthus is stately in formal and informal settings as specimens or small groups. Pair them with hosta, heuchera, ferns, iris, astilbe, epimedium, and Solomon’s seal for gorgeous layered combinations. Annuals like begonia and caladiums share the same growing conditions. Their blooms also make striking cut flowers.
The vigorous growers spread through rhizomes to form clumps. In optimal conditions that mirror their Mediterranean climate, they spread aggressively. Some are invasive in Oregon and California. They root easily and can be difficult to remove once established. Most varieties benefit from being kept in bounds by walkways or edging. In areas with winter climates or hot summers, plants are more well-behaved with less spread. Hybrids are more compact and better behaved, suited to various garden situations.
Characteristics
Bear’s breeches’ long, basal leaves have sturdy central spines and form a rosette. In spring and summer, tall bloom spikes appear with vertical rows of creamy white flowers and purple-rose bracts. The hooded, two-lipped blooms line the spikes and resemble a large foxglove or oversized snapdragon.
The perennials are drought-tolerant, deer and rabbit-resistant, with few pest and disease issues. They may be slow to establish but settle in by the second growing season.
Several of the species are in cultivation. A. mollis and A. spinosus and their cultivars are the most widely grown for ornamental landscapes.
- A. mollis is a popular, historic European species that grows four feet tall and two to three feet wide. The bloom spikes top five feet in late spring and early summer. Individual flowers measure one inch.
- A. spinosus grows three to four feet with summertime blooms in June through August. The flower stalks rise three to four feet tall above the foliage. Leaves are deeply cut with spiny margins.
- A. hungaricus resembles A. spinosus but with slightly less divided, spiny foliage in dense clumps. It has pale pink to white flowers with attractive, ornamental leaves. This species is synonymous with A. balcanicus.
- A. montanus, or mountain thistle, is indigenous to tropical climes of West Africa. Hardy in zones 7 to 10, plants reach four to six feet tall. The shrubby perennial has deeply lobed, symmetrical leaves up to one foot long in silver and dark green. Mountain thistle is most susceptible to winter damage in lower zones.
- A. dioscoridis is native to Turkey, Syria, Armenia, and Iran. It has pink petals in early summer and divided leaves on one to two-foot plants.
- Acanthus sennii, or Ethiopian bear’s breech, grows at high elevations. Dark, glossy leaves have black stems. Late summer and fall flowers are bright red-orange.
Native Area
The ornamentals are native to Mediterranean climate zones with loose, well-draining soils and moderate temperatures. They grow in woodlands and slopes as understory spreaders.
Occurring naturally in arid, mild climates, they may fade in heat and humidity or extreme winter conditions. Some hybrids perform well across zones without aggressive spreading.
Planting
As a rhizomatous spreader, Acanthus gradually forms a clump and continues to sprawl in optimal conditions. Planting it near a walkway or bounded bed helps keep it in check. Root barriers or areas where it has room to run work, too. When planting, space plants three feet apart to allow for air circulation.
Transplanting
Like most perennials, you can plant bear’s breeches year-round, with the best time being spring and fall. Cool temperatures and seasonal moisture give plants time to establish before winter and summer temperature fluctuations. For the least stress on the new plant, avoid frozen or waterlogged conditions and extreme heat or drought periods.
How to Grow
Bear’s breech are carefree, low-maintenance plants. Even so, specific cultural requirements, like regular moisture and dappled light, are best for optimal health and flowering.
Light
Acanthus grows best in partial sun, dappled light, and bright, open shade. Morning sun exposure is best for flowering; they tolerate deeper shade but may not bloom. They also grow in more sunshine in northern climates, with regular moisture. Provide protection from direct afternoon rays that scorch and burn leaves.
Water
Once established, bear’s breeches are drought-tolerant. They enter dormancy in prolonged periods of drought to conserve energy, where leaves die back. Water during dry spells to maintain the best growth and flowering.
While it tolerates a range of conditions, Acanthus doesn’t do well in wet soils. They grow best with consistent moisture from regular water.
Soil
Well-drained, loose, fertile soils are best. They grow in various soil types but do best in organically rich and humusy compositions. They aren’t picky about pH levels and grow in neutral to acidic soils.
Add compost at planting, especially in poor soils like clay and sand. Organic matter helps with aeration, moisture retention, temperature regulation, and nutrition.
Temperature and Humidity
The perennials are evergreen in warm climates, but foliage dies back when temperatures drop below 20℉. Provide a thick layer of mulch to insulate roots in cold winters, as they’re marginally hardy in the lowest growing zones. Leave dormant foliage in place in cold climates for added protection, removing it in early spring before new growth emerges. Late spring frosts may damage buds and blooms.
The Mediterranean natives fade in hot and humid climates, but certain cultivars do well without aggressive spreading, providing plenty of air circulation and moist but not overly wet soils.
Fertilizing
With nutrient-rich, fertile soils, the lush growers don’t require additional fertilizers to thrive. They’ll benefit from fresh compost each spring. To boost lacking soils, apply a balanced organic fertilizer like 5-5-5 in early spring before new growth emerges.
Maintenance
Aside from keeping any vigorous growers in check, Acanthus is easy-care. Deadhead flower stalks after they fade to tidy up and direct energy to the leaves and roots rather than seeding. Maintain a layer of mulch for insulation, moisture, and weed suppression.
Propagation
Propagation is most successful through root division and root cuttings. Seed sowing is another easy method for the patient gardener, as plants take two to three years or more to flower from seed. Plants from seed (other than the straight species) may not be true to type.
Root Division and Cuttings
If you notice leafy shoots popping up around existing plants, dig these rooted sections in spring or fall to expand the colony. Sever the young shoot from the mother plant with a spade, capturing the stem and fibrous roots. Transplant the seedling to its new garden location or container and keep it evenly moist while roots establish.
Take root cuttings when plants are dormant in fall and winter. Dig around the mother plant carefully to expose extending roots. Choose long, thick roots (pencil-size) to clip from the parent, leaving at least two-thirds of the original roots intact.
Cut the root into three-inch sections and place them vertically in pots with well-draining potting media kept evenly moist.
Growing From Seed
To sow bear breeches from seed, collect them off the stems when they ripen and brown in late summer and early fall. Soak them in water overnight, and direct sow them in a prepped garden area, seed tray, or cell pack, covering them with one-quarter inch of seed mix. They germinate best at 50-55°F and sprout in about 25 days.
Popular Varieties
Hybrids abound across the species, with selections tailored to smaller garden spaces and varying climates. The industry standards and award-winners make showy ornamental specimens.
‘Summer Beauty’
A. ‘Summer Beauty’ is a top-performing hybrid between A. mollis and A. spinosus (or A. hungaricus – it’s unknown). It has large, lush leaves that unfurl up to two feet long and are deeply cut. It withstands hot and humid conditions.
The tall bloom spikes of ‘Summer Beauty’ reach four to six feet tall. Vertical rows of creamy white blooms with purple bracts line the stalks.
‘Whitewater’
A. ‘Whitewater’ splashes with bright, creamy white along margins and surfaces. In addition to its unique foliage are tall bloom spikes of pinky-white flowers with deep purple bracts. These emerge in summer and last for weeks.
This one makes a unique container specimen or small-group arrangement. ‘Whitewater’ is hardy in zones 7 to 10 and reaches three to four feet tall.
A. mollis ‘Tasmanian Angel’ is another variegated type, less vigorous than the species, with splashes and white and tinges of yellow on early leaves.
‘Rue Ledan’
A. mollis ‘Rue Ledan’ boasts soft, broad foliage with multi-season interest. Instead of purple bracts, bloom spikes bear white blooms with green hoods in summer.
The Royal Horticultural Society granted this selection the Award of Garden Merit. This is another variety that tolerates hot climates.
Common Problems
The genus is free of most pests and diseases. However, it may occasionally experience slugs and snails and powdery mildew. The best control is prevention through maintaining optimal cultural requirements.
Pests
Slugs and snails may be unwelcome visitors. Hand-pick them early in the day or evening when they’re most active. In the middle of the day, they’ll tuck in under leaves or on the soil around the base of the plants. If numbers increase, bait them with beer or soda traps by filling a shallow dish and placing it at soil level.
Diseases
As with pests, the best disease control is prevention through cultural conditions, mainly by providing adequate moisture and air circulation.
Powdery mildew is one of the most common fungal problems, where the pathogen Erysiphe appears as a grayish-white dust on leaves and stems.
Spores spread on the wind, through contact with infected plants or tools, or by splashing up from the soil via raindrops and irrigation. The spores begin on the leaves and spread to the stems, depleting energy and nutrition.
Leaves turn yellow, distort, and drop during severe infections. Fortunately, powdery mildew is treatable with early detection and doesn’t usually kill the specimens.
Remove the impacted leaves when feasible. For more extensive outbreaks, horticultural oils like neem or insecticidal soaps can treat powdery mildew early on. (but these impact beneficial insects, so be sure to follow application requirements).
Frequently Asked Questions
What’s the best placement for bear’s breech?
Employ these structural growers as specimens or in small groups as a unique groundcover. They add interest when lining a walkway or wall, in the perennial border, or naturalized arrangements under tree canopy. Popular in English gardens, they span formal and informal styles with an architectural, tropical look.
Is Acanthus invasive?
The clump-forming perennial spreads via rhizomes and can be aggressive in its optimal growing conditions. It may become invasive in areas that mirror its Mediterranean or tropical climate, depending on the species. Some varieties are better behaved and, in their lower and upper growing zones, won’t experience the same robust growth.