Acanthus and kin

Monday, 24 November 2008

My parents gave me Acanthus mollis, the old-fashioned oyster plant, when I started my first garden, on the premise that it couldn't be killed, even by a novice.

Acanthus mollis blooms from October to December. From a clump of large, glossy, jagged-edged leaves, arise stately spires to a height of a metre or more comprised of white flowers delicately veined with purple and held within prickly, purplish-brown shell-like bracts. Its foliage forms an attractive groundcover below trees or between shrubs, or can be used as a bold focal point in a smaller garden. The leaves sometimes disappear for a time after flowering but soon return, and they are particularly luxuriant in winter, when the foliage of many other perennials is at its worst. Various cultivars exist, including the lovely gold-leaved 'Hollard's Gold'; 3m-tall 'Bendigo Towers'; and a white-variegated leaved form. Other species, such as Acanthus spinosus with very deeply cut, spiny leaves, can be found, but do not flourish quite as well in Sydney as the more common species.

A member of the broader Acanthaceae plant family (which includes the Justicia genus; Strobilanthes species; and shrubby Mackaya bella which is in bloom at the same time and an ideal shrubby partner for the oyster plant), it shares with its relatives an ease of cultivation; an ability to grow in shady places; lush and attractive leaves; and decorative two-lipped flowers, with four to five petals (one or more of which may be formed in the shape of a protruding tongue), often surrounded by distinctive bracts.

It looks its best in shade or semi-shade, and needs reasonable moisture, and protection from passing snails, which can ruin the foliage. Otherwise, it is an undemanding plant. But ... it is very hard to eradicate if you ever decide to get rid of it, as the tiniest piece of root left behind will become a whole new plant: my parents were right in believing no one could kill it. So it is best regarded as a permanent garden feature and not planted too impulsively. It is also a keen self-seeder, so its flower spikes should be removed and destroyed (not composted) before they set seed.