Cold Hardy Ice Plants: South African Jewels for American Waterwise Landscapes
by High Country Gardens
The Ice Plants (Delosperma) are native to Africa. The cold hardy species of Delosperma are indigenous to the mid- and high elevation mountains and deserts of the Republic of South Africa and its landlocked neighbor and the world’s highest elevation country, Lesotho. The common name Ice Plant refers to the sparkling evergreen foliage of some of the plants in the genus.
History of Coldy Hardy Ice Plant (Delosperma)
In the early 1990’s Panayoti Kelaidis, then Director of Denver Botanic Gardens’s Rock Alpine Garden, began his explorations to South Africa to study its flora. Here he found plants of Delosperma growing in the mountains where there was snow all winter. So he started to test plants of Delosperma cooperi as a possible addition to the intermountain plant palette. Guess what? The plants survived the winter. And over the past 20 years, Delosperma cooperi has not only become a staple groundcover in western Xeriscapes, but started the cold hardy Delosperma revolution. There are now dozens of fantastic species and hybrid cold hardy Ice Plants currently in cultivation with more to come!
Benefits of planting with Coldy Hardy Ice Plant (Delosperma)
I make ample use of this genus in my xeriscapes. In addition to being an excellent source of nectar and pollen for the honeybees, I have found these showy groundcovers to be a perfect match for planting into gravel mulch (a very common component of waterwise landscapes). The plants grow rapidly over the gravel covering the rocks to provide relief from reflected glare and heat while blooming in a rainbow of colors to brighten their planting area. Ice Plants are definitely waterwise and don’t need a lot of supplemental water. But they don’t like to go too dry. I generally water established plants deeply once every week to 10 days if there’s been no rain, to keep their succulent foliage plump and the flowers plentiful.
The Delosperma thrive in poor, infertile, well drained soils. They don’t like to have their roots sitting wet in rich loam or clay. In the Mid-West and Eastern US where there is more precipitation than out West, excellent winter drainage is essential. To help Ice Plants get ready for winter, I always advise gardeners to stop watering their Delosperma in the fall so the plants will stop growing and dehydrate somewhat in anticipation of the freezing winter temperatures to come. In the spring, it is often advisable to cut back the plants by about half their size to remove any winter damaged stems and leaves and revitalize the plants for summer.
Some of my favorite varieties include:
1. Delosperma Firespinner® - The stunning orange and lavender flowers of Firespinner are truly a sight to behold in late spring. The colors stop you in your tracks, the first time you see it. It has been noted that Firespinner needs a least a month or two of winter cold to stimulate spring flowering. So it should not be grown in zone 8-10 warm winter climates; this beauty likes it cold over the winter months.
2.Delosperma ‘Lavender Ice’ – A lovely hybrid introduced by Perennial Favorites Nursery in Rye, CO, ‘Lavender Ice’ has huge, shimmering light lavender-pink flowers and blooms for several months beginning in late spring. I like to plant it with other darker flowered types like ‘Blut’ and D. cooperi for a memorable combination of colors.
3. Delosperma ashtonii ‘Blut’ – discovered as in his Lakewood, Colorado garden, Kelly Grummons, owner of Timberline Gardens, introduced ‘Blut’. This everblooming plant flowers from late spring through summer with the deepest magenta-red flowers you will ever see. The foliage is durable and reliably evergreen. One of my top three.
4. Delosperma sp. ‘Lesotho Pink’ – This High Country Gardens introduction blooms for a month in early to mid-spring covering itself with medium sized clear pink flowers. The foliage grows as a tight mat and looks great year-round. Selected from a group of plants grown from seed collected in Lesotho at an elevation of nearly 11,000 ft. Perhaps one of the most cold hardy species.
Text and photos by David Salman, chief horticulturist