Sempervivum arachnoideum, or Cobweb Houseleek, is a distinctive succulent known for its unique appearance. Its rosettes feature fine, spiderweb-like hairs, giving the plant its characteristic name. These hardy, low-maintenance plants are a favored choice for rock gardens, containers, and drought-tolerant landscapes. They form tight, evergreen rosettes, creating a visually appealing, carpet-like effect.
Essential Care Requirements
Sempervivum arachnoideum is a low-maintenance succulent, but specific conditions help it thrive.
Light
Sempervivum arachnoideum thrives in full sun, though it tolerates partial shade. Bright, direct light maintains compact growth and vibrant colors. Insufficient light causes etiolation, where the plant stretches and becomes leggy, losing its characteristic form.
Soil
Well-draining soil is crucial for Sempervivum arachnoideum. Use a specialized succulent or cactus mix, or amend regular potting soil with perlite, pumice, or coarse sand to improve drainage. Avoid heavy, water-retentive soils, which can cause root rot. The ideal soil pH ranges from 6 to 8.
Watering
Sempervivum arachnoideum is drought-tolerant, storing water in its fleshy leaves. Use the “soak and dry” method: water thoroughly, then allow the soil to dry completely before watering again. Reduce watering in cooler months or during dormancy, as overwatering is a common cause of decline.
Temperature and Hardiness
This plant exhibits exceptional cold-hardiness, tolerating freezing temperatures across USDA zones 5 to 8. While resilient to cold and heat, it prefers average summer temperatures between 65°F and 75°F (18°C and 24°C). This allows it to thrive outdoors year-round in many regions.
Fertilization
Sempervivum arachnoideum has low nutrient requirements and thrives without frequent fertilization. If desired, apply a highly diluted, balanced liquid fertilizer (e.g., 5-10-5 NPK) sparingly during the spring or early summer growing season. Over-fertilization can lead to leggy growth or loss of vibrant coloration.
Planting and Repotting
When planting Sempervivum arachnoideum, choose containers with ample drainage holes or garden spots with good water runoff, like rock gardens or slopes. These plants prefer well-drained, gritty soil. When planting a new rosette or “chick,” gently settle it into the prepared soil, ensuring roots are covered but the rosette is not buried too deeply.
Repotting is typically needed every one to two years when the plant becomes root-bound or the soil degrades. Spring is an ideal time, allowing the plant to adjust during its active growing season. Handle the plant gently to avoid damaging roots. Choose a pot slightly larger than the previous one, ensuring excellent drainage.
Propagation and Lifecycle
Sempervivum arachnoideum primarily reproduces through offsets, called “chicks” or “pups.” These miniature rosettes form around the mother plant, connected by short stolons. Once chicks are at least a quarter the size of the mother rosette and have developed roots, they can be separated and planted in well-draining soil. Spring or early summer is the best time for this.
Propagation from seeds is also possible, though less common for home growers. A unique aspect of this plant’s lifecycle is its monocarpic nature: the mother rosette flowers once, typically in mid to late summer, producing tall stalks with pink to red flowers, and then dies. However, numerous offsets produced before flowering ensure the plant’s continuation, filling any gaps left by the spent mother rosette.
Troubleshooting Common Issues
Rot is a common issue, usually caused by overwatering or inadequate drainage. Symptoms include mushy leaves and general plant decline. To prevent rot, ensure the soil dries completely between waterings and use a fast-draining mix. Early detection may allow recovery by reducing watering and improving drainage, but severely affected plants may not recover.
Sempervivum arachnoideum is generally pest-resistant, but mealybugs or aphids may appear. Mealybugs are small and cotton-like, while aphids form clusters on new growth. Organic control methods, such as dabbing mealybugs with rubbing alcohol or spraying with insecticidal soap or neem oil, can manage infestations.
Etiolation, or stretching, occurs due to insufficient light, causing rosettes to lose their compact form. Gradually move the plant to a location with more direct sunlight to remedy this. Soft or wrinkled leaves indicate either underwatering or overwatering. Mushy leaves suggest overwatering, while dry, shriveled leaves indicate a need for water. Adjusting the watering schedule based on soil moisture resolves these issues.