Closely related to the smaller and better-known Sisyrinchium, Libertia is a useful and elegant genus of Southern Hemisphere perennials.
Although the plants most commonly encountered in the horticultural trade are those described as Libertia grandiflora, much material with this label is more likely to be a strain of the South American L. chilensis Formosa group (the true L. grandiflora, a New Zealand species, is less hardy, and less often seen).
The Chilean species is renowned for its early summer display of attractively open, clear white flowers with pale yellow anthers held on upright stems above the sword-shaped evergreen foliage.
Seed pods in late summer offer additional ornamental value. (Seed-raised plants exhibit a high degree of variability in flower size and inflorescence length, potentially offering interesting opportunities to the breeder.)
Plants eventually grow into substantial clumps exceeding 1m diameter and cope with partial shade, though they thrive best on open sites and well-drained soils, where they will prove hardiest and flower most prolifically. Although established plants are hardy in all but the coldest winters, foliage can brown and die back in periods of prolonged frost: plants can be refreshed by combing out the dead leaves and shearing back the clump in early spring.
In short, these are ideal city plants: robust, long-lived, adaptable and attractive. As a bonus, sharp crystals of calcium oxalate in the leaves render the foliage unpalatable to grazers and other pests. And their tendency to self-seed, but not aggressively, makes them an ideal component of dynamic, ecologically-based planting schemes, such as Nigel Dunnett’s influential planting at London’s Barbican.
Libertia thrives there on a windy site well above street level, in shallow soil and without irrigation, providing structural and ornamental interest throughout the year, proof of its value as an urban landscape plant.
By Martin Deasy, a tutor on the RHS Mhort. He also runs his own landscape design business.