How to Grow Cobweb Houseleek
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Cobweb Houseleek
Sempervivum arachnoideum
succulentA low-growing, mat-forming succulent with distinctive rosettes covered in fine white hairs that resemble spider webs, giving it its common name. This hardy alpine plant produces dense clusters of compact rosettes and sends up thin flower stalks with star-shaped pink to red flowers in summer. It is extremely cold-hardy and drought-tolerant, making it ideal for rock gardens, alpine troughs, and container cultivation.
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Example Cobweb Houseleek timeline · Pittsburgh, PA (Zone 6b)
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Plant Cobweb Houseleek
Around Apr 17Near Pittsburgh's average last spring frost.
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Tend & protect
Late spring–summerWatering, feeding, and pest-watch reminders.
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Harvest Cobweb Houseleek
Late summer into fallBefore the first fall frost (≈ Nov 8)
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Growing Conditions
Soil
Growing Zones
Find your zone →Thrives in zones 3-9; extremely cold-hardy and well-suited to alpine and temperate climates
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Get my Cobweb Houseleek timeline →Growth Stages
Establishment
2-4 weeksYoung rosettes are small, compact, with fine webbing visible; foliage may be pale green to reddish
Plant in spring; water lightly until roots establish (2-3 weeks). Avoid overwatering. Provide excellent drainage.
Vegetative Growth
Spring through early summer (8-12 weeks)Rosettes expand, webbing becomes more prominent, plants produce small offset rosettes around the parent
Water sparingly during growing season (spring-early summer). Fertilizer is rarely needed; if used, apply dilute cactus fertilizer once in spring. Monitor for excess moisture.
Flowering
6-10 weeks (June-August depending on zone)Thin, reddish flower stalks emerge from the center of mature rosettes; star-shaped flowers in pink, red, or magenta appear
Flowering typically occurs only once per rosette; the rosette dies after flowering but offsets ensure plant continuity. Do not deadhead if offsets are present.
Offset Development
Late summer through fall (8-12 weeks)After flowering, small rosettes develop around the base of the parent rosette, creating dense clusters and colonies
Allow offsets to grow and establish before dividing. Continue sparse watering. Remove dead rosette material in fall or early spring.
Winter Dormancy
November through March (4-5 months)Rosettes become compact and may deepen in color; growth slows significantly in cold climates
Minimal watering needed. Ensure excellent drainage to prevent rot. No fertilizer. Protect from excessive winter moisture; snow cover is beneficial in harsh climates.
Companion Planting
Plan your garden →Plant with:
Avoid planting near:
Common Pests
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Remove affected rosettes; spray remaining plants with insecticidal soap or neem oil; ensure excellent air circulation and avoid overwatering
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Increase humidity slightly if in very arid conditions; spray with water to dislodge; use miticide if severe; ensure good air circulation
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and
Remove by hand, especially in damp conditions; use copper tape barriers around pots; reduce moisture; beer traps in garden beds
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Repot in fresh, dry, gritty soil; reduce watering; improve drainage; remove affected portions; treat with fungicide if necessary
Uses
Living Roof and Green Roofing
CraftSempervivum arachnoideum is widely used in green roof systems and living roof installations due to its extreme hardiness, drought tolerance, and shallow root system. These plants require minimal maintenance and soil depth, making them ideal for extensive green roofs in cool climates. [source]
Alpine Container and Trough Gardening
HouseholdThe tight, compact rosette form and distinctive webbed appearance make cobweb houseleek a premium choice for alpine troughs, alpine sinks, container gardens, and tabletop displays. Its extreme cold-hardiness allows container gardens to winter outdoors in even harsh climates. [source]
Rock Garden and Xeriscaping
CraftThis succulent thrives in rock gardens, scree beds, and xeriscape landscapes where water conservation and minimal maintenance are priorities. Its structural form and color changes provide year-round visual interest with virtually no irrigation needed after establishment. [source]
Traditional Herbal Remedy
MedicinalIn European folk medicine, Sempervivum species (including S. arachnoideum) have been used topically for skin conditions, burns, and wounds. The succulent leaves contain compounds with potential antimicrobial and anti-inflammatory properties, though modern clinical evidence is limited. [source]
Pollinator-Friendly Flower Source
WildlifeThe pink and red star-shaped flowers attract bees, butterflies, and other pollinators in early to mid-summer, providing an early season nectar source in alpine and temperate gardens. The flowers bloom over an extended period, offering sustained food resources. [source]
This is not medical advice. LizPlants is not a medical resource. Always consult a qualified healthcare professional before using plants medicinally.
Harvest Tips
Sempervivum arachnoideum is ornamental and not typically harvested for consumption. However, offsets can be divided and propagated year-round for sharing or expanding your collection. Gently remove offset rosettes with a small section of root and allow to dry for 1-2 days before replanting in gritty soil. For the best visual display, mature plants are left in place to form dense colonies over several years.
Fun Facts
- 🌱 Sempervivum arachnoideum is named for the fine white hairs covering its rosettes, which resemble a cobweb—the scientific name 'arachnoideum' derives from the Greek word for spider ('arachnid'). These hairs are actually trichomes that help the plant reduce water loss and reflect intense alpine sunlight.
- 🌱 Sempervivum is derived from Latin words meaning 'always living'—a fitting name, as the rosettes can survive in harsh alpine environments with minimal resources. One parent rosette's leaves can be used to propagate dozens of new plants, making it nearly impossible to kill or lose the species.
- 🌱 This species originates from the high mountains of the Pyrenees and eastern Alps, where it thrives at elevations of 6,000-10,000 feet in rocky crevices with poor soil and intense UV exposure. Its extreme cold-hardiness (surviving to -40°F or below) makes it hardier than nearly any flowering plant cultivated in northern gardens.
Gardening Terms
New to gardening? Learn about terms used in this guide:
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