Sempervivum calcareum
| Light | Bright light to full sun; happiest outdoors year-round |
|---|---|
| Water | Sparingly; let the soil dry fully between waterings, keep dry in winter |
| Soil | Gritty, sharply draining mineral mix (see Soil and potting mix) |
| Temperature | Fully cold-hardy; tolerates hard frost when dry (roughly USDA zones 5–8) |
| Propagation | Offsets (the easy, standard method); seed |
| Toxicity | Non-toxic to cats and dogs |
Sempervivum calcareum is a cold-hardy alpine succulent forming tidy, symmetrical rosettes of blue-green leaves, each tipped with a distinct patch of red-brown or purple. Native to the southwestern Alps, on the border of southeastern France and northwestern Italy, it is one of the most admired of all the houseleeks among alpine and rock-garden growers, prized for the crisp contrast between its glaucous foliage and those neatly painted leaf tips.
Description
Sempervivum calcareum forms open, flattened rosettes typically 6–10 cm across, though robust plants in good conditions can be larger. The leaves are broad at the base and taper to a firm point, coloured a cool grey- to blue-green and finished with a well-defined chestnut, red-brown or purplish tip — the feature that makes the species so instantly recognisable. The tip colour deepens in bright light and cold weather, and fades toward plain green in shade.
Like all houseleeks it is monocarpic: an individual rosette flowers once, sends up a stout stem carrying a cluster of pale, star-shaped flowers, and then dies. This is nothing to mourn, because each parent rosette produces a ring of offsets on short runners long before it blooms, so the colony renews and spreads itself continuously.
Distribution and habitat
The species is native to the southwestern Alps, ranging from the Dévoluy massif of southeastern France across to neighbouring northwestern Italy, where it grows on rocky slopes, ledges and screes at moderate altitude. True to its name, it is largely a plant of limestone country, colonising calcareous rock and gritty, fast-draining ground and taking full mountain sun, drought and hard winter frost in its stride. These alpine origins are exactly why it is so tough and undemanding in cultivation.
Cultivation
Sempervivum calcareum is one of the easiest succulents to grow and an ideal outdoor plant. Give it a gritty, sharply draining mix with plenty of coarse mineral material, and the sunniest spot you can offer — strong light is what keeps the rosettes compact and brings out the richest tip colour. In too much shade the leaves stretch, pale and lose their character.
Water sparingly during the growing season, letting the substrate dry completely between drinks, and keep the plant dry through winter, when it is fully frost-hardy and needs no protection beyond good drainage. It thrives in troughs, rock gardens, alpine pans, wall crevices and green roofs. See Watering and Repotting for general technique; crowded colonies are easily lifted, split and replanted every few years.
Propagation
Propagation could hardly be simpler. The plant obligingly makes offsets (often called "chicks") on short stolons around each rosette; detach a rooted or nearly-rooted chick, settle it on the surface of gritty compost, and it establishes in no time. This is the standard and most reliable method — see Propagation — offsets.
Seed is also possible and is how new variation arises, but seedlings are slower and, because Sempervivum hybridise freely, will not necessarily come true to the parent. See Propagation — seed if you want to experiment.
Common problems
- Rot — the main risk, almost always from wet, poorly drained soil, especially in winter; sharp drainage and dry cold prevent it.
- Etiolation — too little light stretches the rosettes and washes out the leaf-tip colour.
- Pests — mealybugs, vine weevil grubs and aphids can trouble plants, particularly under glass; outdoor plants are usually little bothered.
- Rosette death after flowering — normal and expected, as each rosette is monocarpic; the surrounding offsets carry the colony on.
See also
- Sempervivum — the genus overview
- Propagation — offsets · Soil and potting mix · Watering · Repotting · Pests and diseases