Cold-hardy succulents go to extremes

The Atlas Mountains ramble across northern Africa, rising up from the southern Mediterranean coast. They span from Morocco east to Tunisia, rising as high as the Alps above deserts to create a remarkably cold and dry habitat for plants.

Most gardeners haven’t heard of these ranges, although they are mentioned on the news more than ever as war spreads through the Middle East.

This is the homeland of many sempervivums, an incredibly cold-hardy genus of succulents that takes snow and drought in stride. Most succulents are from balmy southern Africa, where frost is rare, and the majority of them are too tender for frost-tinged gardens. But if you vicariously climb the Atlas Mountains by exploring these widely available plants, you’ll quickly appreciate their tough beauty and versatility.

With 40 genera bred into 4,000 named varieties, this is an enormous group that is a mainstay of colder northern European gardens, where much of the early breeding began. Long grown in Europe and Britain, they were dubbed “house leeks” because, as succulents, they grow well in roof thatch.

Originally it was thought succulents helped reduce fire hazards by keeping thatch moist via root networks that would snuff out embers after lightning strikes. Their ability to live in straw over a long time without soil led to their oldest name, “live forever” — the literal translation of sempervivum.

Sempervivums are rosette-shaped, ranging from an inch across to much larger. The traditional usage is in rock gardens, where they are tucked into gaps to hold the earth in place with their dense coverage. As they age, they spread via offsets into larger patches of plants. Those such as Sempervivum arachnoides produce white webby offsets on the end of long stems — a feature that allows the plant to dangle off stone faces for a waterfall of color.

The most popular way to grow them when the weather is colder is in heavy stone troughs and bowls able to stand out in the winter cold. These can be set on pedestals or raised surfaces to bring the miniature sedums and others up to eye levels, allowing their geometry and textures to be better appreciated.

More recently the sempervivums are creeping into small tray or dish gardens for the patio or indoors, blended with less-hardy accent succulents. Often these are mixed into sparkling natural minerals, glass balls and colored gravels to create lovely, small compositions.

When getting started with sempervivums, remember that the Atlas Mountains are dry and soils extremely well drained so these plants appreciate similar conditions in pots. Use cactus potting soil or make your own by mixing sharp sand with equal parts quality potting soil for the optimal balance between drainage and fertility.

The best part about introducing a new succulent plant to your garden is the ease of propagation. That original becomes the mother of many babies when you sever and root offsets into a new freestanding plant.

With hardy succulents, cold-climate gardeners can still enjoy the exciting new look without concern for frost. Grow in rocks, pots or anywhere elevated enough to ensure perfect drainage for jewel box beauty that lives forever outdoors, just as nature intended.

This story was originally published January 21, 2016 at 12:25 PM with the headline "Cold-hardy succulents go to extremes."