Delosperma
Delosperma is a large genus of trailing or mat-forming succulents in the ice plant family Aizoaceae, native mainly to southern and eastern Africa. Widely grown as low, spreading groundcover, several species are prized as cold-hardy ice plants — plants that shrug off frost far better than most succulents while carpeting themselves in masses of shimmering, daisy-like flowers through the warm season. The genus name, from the Greek for "visible seed", refers to the seeds lying exposed in the open capsule rather than hidden beneath covering membranes as in some related genera, and among mesembs (the informal name for the many succulent genera of the Aizoaceae) Delosperma is one of the most familiar to temperate gardeners.
Description
Most Delosperma are low, sprawling or mat-forming perennials with fleshy, three-sided or cylindrical leaves borne in opposite pairs along creeping stems. The leaves are often studded with tiny glistening bladder cells that catch the light and give the whole plant a frosted, crystalline sheen — the source of the "ice plant" name. Stems root as they trail, so a single plant can knit into a dense carpet a few centimetres tall and a metre or more across.
The flowers are the main event: solitary, daisy-like blooms (technically not daisies at all, but many-petalled mesemb flowers) in vivid magenta, purple, pink, orange, yellow, white or bicolours, often with a paler or contrasting central eye. They open in sunshine and close in dull weather or at night, and a well-grown mat can flower for much of the warm season. The genus is distinguished from close relatives partly by its capsule structure, which splits open to reveal its seed chambers when moistened.
Distribution
The genus is centred on southern Africa — South Africa, Lesotho and neighbouring countries — with a scatter of species reaching into eastern Africa and the Arabian Peninsula. Habitats range widely, from hot, arid lowlands to high-altitude grasslands in the Drakensberg and Lesotho highlands. It is those high-mountain species, adapted to snow and hard frost, that gave rise to the cold-hardy garden ice plants now grown across temperate regions.
Notable species
- Delosperma cooperi — the classic trailing hardy ice plant, smothered in bright magenta-purple flowers; one of the most widely grown groundcovers in the genus.
- Delosperma nubigenum — a low, very cold-hardy mat with yellow flowers and foliage that flushes red in winter.
- Delosperma congestum — compact and hardy, with clear yellow blooms in spring.
- Delosperma echinatum — the "pickle plant", grown more for its bristly, cucumber-like leaves than its small pale flowers; less cold-hardy and often kept as a houseplant.
- Delosperma sutherlandii — a high-altitude species with pink, pale-centred flowers over rounded grey-green foliage.
Many of the vividly coloured plants sold in garden centres are named hybrids and selections rather than pure species; see the cultivar notes below.
Cultivation
Delosperma are among the easiest succulents to grow where drainage is good and light is strong. Give them full sun — flowering falls off sharply in shade — and a gritty, fast-draining mix or a lean, sandy garden bed. They are drought-tolerant once established but flower more freely with occasional summer water; the one thing they will not forgive is wet, heavy soil, especially in winter.
The hardy species tolerate frost and even snow provided their roots stay dry and sharply drained, and are widely used as groundcover on slopes, rockeries, green roofs and gravel gardens. In cold, wet-winter climates, winter damp is far more dangerous than cold itself — raised, gritty beds or container culture with a dry winter rest give the best results. Tender species such as D. echinatum are better treated as tender succulents or houseplants and protected from frost. See Repotting and Pests and diseases for general care; mealybugs and root rot from overwatering are the usual troubles.
Propagation and hobby notes
Delosperma propagate very easily from stem cuttings, which root quickly in gritty mix during the growing season — the simplest way to bulk up a favourite colour or reset a leggy old mat. They also grow readily from seed, though seed-raised plants vary and named colours will not come true. Trailing stems that have rooted along the ground can simply be lifted and divided.
For growers, the genus is best known through its garden hybrids: a wave of vividly coloured, long-flowering selections (often sold under trademarked series names) has made hardy ice plants a mainstay of low-water landscaping. These are typically maintained vegetatively from cuttings to keep their colour true. When buying, it is worth checking a plant's parentage, as cold-hardiness varies a great deal between the mountain species and the tender lowland ones.
See also
- Aizoaceae — the ice plant family
- Delosperma cooperi · Delosperma echinatum
- Soil and potting mix · Watering · Propagation - cuttings · Propagation - seed · Pests and diseases