Culture
Winter hardy to USDA Zones 6-10 where it is best grown in average, fertile, medium moisture, well-drained soils in full sun to part shade. 'Summer Beauty' is noted for having much better tolerance for hot summer weather than A. mollis. Plants tolerate a wide range of soils except poorly-drained ones. Plants may not flower well in too much shade. Late spring frosts can impair or eliminate flowering for the year. Remove flowering stalks after bloom. In cold winter areas, plant foliage should be left in place over winter but removed in early spring as new foliage appears. Plants can spread invasively by creeping rootstocks, particularly in loose soils. Unwanted spread can be addressed by root barriers. Plants generally spread less in the northern parts of their growing range. Plants may be propagated from root cuttings taken in early spring. Plants are often slow to establish in the garden, but may become somewhat difficult to eradicate once established since small sections of root left behind can sprout new plants.
Noteworthy Characteristics
Acanthus is a genus of about 30 species of herbaceous perennials native to the Mediterranean, Asia and Australia. These plants bear distinctively spiny foliage and flowering stalks. It is believed that the leaves of A. mollis or A. spinosis were the model for the sculptured leaves that adorn the capitals of the Corinthian columns that became popular in the 4th century B.C.
Genus name comes from the Greek word akantha meaning spine in reference to the toothed edges on leaves in some species.
There appears to be no scholarly agreement among authorities on the origin and meaning of the term bear’s breeches.
'Summer Beauty' (Acanthus mollis x Acanthus spinosus) is a clump-forming hybrid that features both attractive foliage and architecturally bold flower spikes. Deeply-lobed, soft-spiny, glossy, dark green leaves (to 2’ long) form an attractive mound of basal foliage to 2 1/2' tall. Creamy white snapdragon-like flowers, each hooded and subtended by spiny purple bracts, bloom in late spring to midsummer in vertical rows on substantial flower spikes that rise well above the foliage mound to 4-6’ tall.
Problems
Susceptible to powdery mildew. Snails and slugs are occasional visitors that can do substantial damage if left unchecked. Plants can spread aggressively in optimum conditions.
Uses
Bold, stately plants that may be grown as specimens but are perhaps best in small groupings. Borders or formal gardens.