The immortal acanthus will make a majestic statement in your border
For such an elegant plant in flower, its common name of bear's breeches seems less than suitable. But this rather fanciful name has the merit of being easy to remember. The botanical name of acanthus is not difficult either and connects the plant to its illustrious past.
The word acanthus means spiny and this Mediterranean native certainly is spiny. Acanthus was used in herbal medicine during ancient times. It was associated with immortality, which, even now, is easy enough to understand as this plant is very tenacious and long-lived. A stylised version of the shape of the acanthus leaves was frequently carved into the top of Roman and Greek columns.
There are two main kinds grown in gardens: acanthus spinosus, which has spiny leaves, and the soft-leaved acanthus mollis. The spiny kind is grown for its much-divided and spiny leaves. Although it is spiny, the spines are not dangerous like those of cactus, but they might be a deterrent to grazing animals who tried a mouthful. The soft acanthus has broader, less divided leaves and few, if any spines. Lacking the picturesque spines, this plant is not so dramatic but it makes an excellent display of well-shaped leaves. In both species, the mound of foliage is generally evergreen, except in a harsh winter or in a very exposed place.
The large rosette of handsome leaves produces tall flower spikes to head-height, though often less if the ground is well drained. The spiny species flowers in early to mid-summer, the soft species in July and August. The flower spikes resemble foxglove spires but they are not related and the acanthus stems are stronger and last longer.
The flower spikes are green as they grow upwards. Each spike carries 30 or 40 individual flowers. Over each flower, a hooded purple bract forms for protection of the delicate flower parts. Under the bracts, the white flowers appear. The bracts stay in place after the flowers are shed and rounded pods form under the bracts.
The seed heads can last a long time and, though less colourful than the flowers, provide a strong upright shape. Acanthus tolerates light shade because it is so robust, but unfortunately it often develops a chalky covering of powdery mildew when grown there.
It prefers a sunny spot in well-drained soil of reasonable fertility. It can be invasive, and it needs a good deal of space for the large leaves. If old plants are dug out and moved, the roots left behind will re-establish the plant.
Acanthus has tremendous presence, and can be grown in a mixed border with shrubs and other herbaceous plants.