Sempervivum calcareum
houseleek
Southwestern Alps (France and Italy)
Overview
Sempervivum calcareum is an evergreen, mat-forming succulent that produces rosettes 2–3 inches (5–8 cm) across, each made of fleshy, blue-green leaves tipped with a sharp reddish-brown to maroon point. The rosettes hug the ground and spread by short stolons that carry small offset rosettes, building dense colonies over time. Foliage colour deepens to bronze and red tones in cold weather and strong sun. In summer a mature rosette sends up a thick stem 4–10 inches (10–25 cm) tall topped with a flat cluster of pale pink star-shaped flowers; that flowering rosette then dies, leaving the surrounding offsets to fill the gap. The species grows on rocky alpine and Mediterranean slopes and tolerates heat, drought, poor soil, and cold once established, though it rots in wet, poorly drained ground, and in shade the rosettes grow loose and lose their tight form. Hardiness covers USDA zones 5–9. The evergreen rosettes hold through winter. It is grown in rock gardens, troughs, green roofs, and the cracks of dry walls where drainage is sharp.
Native Range
Sempervivum calcareum is native to the southwestern Alps of France and Italy, where it grows on limestone rocks, screes, and dry stony slopes at montane to subalpine elevations.Suggested Uses
Sempervivum calcareum is used in rock gardens, alpine troughs, green roofs, gravel gardens, and the crevices of dry stone walls. It suits shallow containers and sunny, sharply drained pockets. The low evergreen rosettes work as edging and ground cover on poor, dry sites.How to Identify
Appearance
Size & Dimensions
Height3" - 4"
Width/Spread8" - 1'
Colors
Bloom Information
Flowering occurs in summer, usually June to August in the Northern Hemisphere, when mature rosettes raise pink star-shaped flowers on stout stems for about 2–3 weeks. Only rosettes that flower die afterward, while the offsets continue. Many rosettes never flower in a given year. The main interest is the evergreen foliage rather than the bloom.
Detailed Descriptions
Foliage Description
Blue-green with maroon tipsGrowing Conditions
Sun Requirements
Requires 6-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Grow Sempervivum calcareum in full sun and very well-drained, gritty soil, such as a rock garden, trough, or gravel bed. Water sparingly; the succulent stores moisture and rots in soil that stays wet, especially in winter. It needs no feeding and grows on poor, stony ground. In shade the rosettes loosen and stretch, losing their compact form and colour. Spent flowering rosettes are removed after they die to keep colonies neat. The main problems are crown and root rot from excess moisture and, occasionally, vine weevil grubs in containers.Pruning
Sempervivum calcareum needs no conventional pruning. Spent rosettes that have flowered and died are lifted out, and surrounding offsets fill the space. Overcrowded mats are thinned and offsets replanted to renew a colony.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
summer
Container Growing
✓ Suitable for container growing
Minimum container size: 1 gallons