Cobweb Houseleek Care (Sempervivum arachnoideum)

This alpine succulent thrives in bright outdoor light with a distinct preference for direct sun.

• Provide 6–8 hours of direct sun daily; morning sun plus light afternoon sun brings compact rosettes and strong cobwebbing on Cobweb Houseleek.
• Tolerates light partial shade, especially in hot climates, but rosettes may stretch and lose color if daily direct sun drops below 3–4 hours.
• In very hot summers, protect from harsh late-afternoon sun with light shade to reduce leaf scorch, especially on shallow or stone trough plantings.

This species is drought-tolerant and prefers infrequent, deep watering over light, frequent applications.

• Water only when the top 3–5 cm of soil are completely dry; in many outdoor rock gardens this may mean every 1–3 weeks in summer, less in spring and fall.
• Use sharply draining, gritty soil so water runs through within seconds; standing water or a heavy mix quickly leads to root rot in Sempervivum arachnoideum.
• Reduce watering in cool or wet seasons; wrinkling leaves signal thirst, while mushy, translucent leaves indicate overwatering and require longer drying intervals.

This hardy succulent is adapted to wide outdoor temperature swings, especially in temperate climates.

• Ideal growing temperatures are 60–75°F (16–24°C) during the active season, with cooler nights helping maintain compact rosettes.
• Mature plants tolerate cold down to about 0°F (−18°C) in well-drained soil; brief dips slightly below are often survivable if crowns stay dry.
• Handles summer heat up to 90–95°F (32–35°C) if soil drains fast and rosettes receive some protection from intense late-afternoon sun.

Humidity is rarely a concern, as this alpine succulent prefers dry air.

• Aim for 20–40% humidity; typical indoor or outdoor dry air suits Cobweb Houseleek well.
• Watch for rot, pale mushy leaves, or fungal spots as signs humidity is too high, especially in warm, still air.
• Increase air movement and space between rosettes instead of adding moisture if conditions feel humid.

Sempervivum arachnoideum needs very fast-draining, mineral-based soil to prevent root and crown rot.

• Use a gritty mix such as 60–70% mineral material (coarse sand, fine gravel, pumice, or perlite) with 30–40% lean potting mix or compost.
• Aim for slightly acidic to neutral pH around 6.0–7.5, avoiding strongly acidic or alkaline substrates that can limit nutrient uptake.
• Create a shallow, sloping planting surface so water sheds away from rosette centers and does not pool around the crown.
• Avoid heavy, compacted, or high-peat soils that stay wet and instead incorporate coarse particles to improve aeration and rapid drainage.

This species is very suitable for container growing, including shallow bowls and troughs.

• Choose a shallow, wide container so offsets can spread while the relatively short roots still access the full soil volume efficiently.
• Prefer unglazed clay pots when possible, as they evaporate moisture faster and lower the risk of prolonged wetness around the roots.
• Elevate containers on feet or pot risers so drainage holes stay clear and water cannot collect under the base after rain or watering.

This succulent needs very light feeding, as it is adapted to poor, rocky soils.

• Use a diluted balanced liquid fertilizer (around 10-10-10) at 1/4 strength in spring to midsummer for Cobweb Houseleek.
• Apply no more than 1–2 light feeds per growing season to avoid soft, weak growth.
• Skip fertilizer in fall and winter when growth slows or stops.
• Compost worked into very lean container mix at planting can replace liquid feeding.

Pruning needs for Sempervivum arachnoideum are minimal and mostly cosmetic.

• Best time to prune is during active growth in spring or early summer.
• Gently remove dead rosettes, dried leaves, and any damaged or diseased parts by hand or with small snips.
• Thin out crowded offsets to maintain a compact, open mat and better air flow.
• Cut off spent flower stalks at the base once they dry to keep the plant tidy.

This species prefers to stay slightly cramped and is repotted or transplanted only occasionally.

• Check for roots circling the container drainage holes or noticeably slow growth as signs it needs more space.
• Plan repotting or transplanting in spring to early summer, about every 3–5 years in containers.
• Use a shallow, wide pot or well-drained rock garden spot with gritty, low-organic soil.
• Handle rosettes gently, disturb roots as little as possible, and water lightly after moving to reduce stress.

Sempervivum arachnoideum is commonly propagated from offsets rather than seed.

• Separate offsets (young rosettes) in spring or early summer when they are thumb-sized and well rooted.
• Lift the mat gently, cut or pull offsets away with a short section of stolon attached, and replant shallowly.
• Use a very gritty, fast-draining mix and bright light to encourage quick rooting.
• Seed propagation is possible but slow; sow on the surface of a sterile, sandy mix and keep barely moist.

This hardy succulent tolerates considerable frost and usually needs little winter care in the ground.

• Mature plants in well-drained soil often handle freezes down to at least 0°F without additional protection.
• In very wet winters, provide a gritty top dressing or slight gravel mulch to keep crowns from sitting in water.
• Move containers to a sheltered, unheated spot with good light to avoid waterlogged, frozen soil.