There are a number of different "ice plants." However, plant taxonomy places the types with which we deal here in the genus Delosperma. That genus contains a number of species; in this article, we use purple ice plant (Delosperma cooperi) as an example. Delosperma cooperi (sometimes given as Mesembryanthemum cooperi) is also called "hardy ice plant."
Delosperma cooperi is a flowering, succulent perennial.
The book, Hardy Succulents, by Gwen Moore Kelaidis, was useful in my research into purple ice plants. As their name suggests, they have light purple flowers, which are daisy-like. The flowers bloom all summer.
Kelaidis remarks that purple ice plants can spread to as much as 3 to 4 feet across. They stay relatively short (about 3 inches tall) and are procumbent inhabit. The rounded, fleshy fingers of the foliage are about an inch long; the green summer color of the leaves may morph into darker colors as temperatures drop.
Planting Zones, Sun and Soil Requirements
This succulent is indigenous to South Africa, where it is an evergreen. Belying its origin, this hardy perennial can be grown in planting zones 5-9. At the northern end of this range, however, note 2 things:
- Winter hardiness is not a given. Purple ice plant may not survive a difficult winter in zone 5.
- Its leaves will not be evergreen, even if it does survive; treat it as an herbaceous perennial.
Planting it in full sun and in a superbly well-drained soil are critical steps to growing this sun-loving ground cover successfully. Avoid planting in a clayey soil unless you are willing to improve percolation there with soil amendments. Purple ice plants are drought-resistant plants and do not require rich soils, but they hate to be sitting in water.
Despite their resistance to drought and dislike of wet feet, they will profit from an occasional watering in the heat of summer, as long as the drainage is excellent.
Uses, Caveats for Purple Ice Plant
The drought tolerance of purple ice plant makes it useful for xeriscaping. Naturals for rock gardens, these succulents can also be planted between the stones in a dry-wall stone retaining wall. Delosperma cooperi, which spreads more vigorously than some types, makes a good groundcover.
Certain types are considered invasive plants in California; e.g., Carpobrotus.
It is not so much cold weather in zone 5 that will kill purple ice plant as it is freezing temperatures combined with wet conditions. Thus it is more likely to survive in a zone 5 region with an arid climate. Kelaidis recommends "a winter blanket of woven row cover (like Reemay)" to help over-winter it in wetter zone 5 climates.
Reduce watering in fall to help harden it off for winter, as cold will be less likely to damage the succulent leaves if they are not quite so full of water.
As a side note, the water-retentive quality of this succulent's foliage makes it a fire retardant plant.
Origin of the Common Name
According to the New Mexico State University extension, the common name for the plants derives from the fact that "they have bladder-like hairs on the leaf surface that reflect and refract light in a manner to make it appear that they sparkle like ice crystals."
Kelaidis mentions a number of other varieties besides Delosperma cooperi; for example:
- D. basuticum 'White Nugget' has white flowers.
- D. 'Gold Nugget' bears yellow flowers.
- D. 'Kelaidis' has the most unusual flower color, a salmon-pink.
In addition to flower color, such features as size and growing requirements distinguish one variety from another. For example, Kelaidis calls 'White Nugget' "more of a clump-former than a ground cover" (that is, it does not spread vigorously enough to be considered as effective a ground cover as Delosperma cooperi). She also indicates that Delosperma nubigenum, a variety with yellow flowers, tolerates clayey soils better than does purple ice plant.