Sempervivum arachnoideum [sem-per-VEE-vum, a-rak-NOY-dee-um] is a species of flowering plants in the family Crassulaceae originating from the Alps, Carpathians, and the Apennines.
The name translates to ‘always alive spider web.’
This translation is a perfect representation of the succulent as it’s an evergreen perennial, producing a mat of fleshy green or reddish-green rosettes with white cobweb-like hairs at the top.
Common names include:
- Cobweb Houseleek
- Cobweb Hens and Chicks
- Cobweb Sedum
Sempervivum Arachnoideum Care
Size & Growth
Sempervivum arachnoideum is a low-growing succulent reaching a height of about 3” inches.
Each rosette measures about 1” – 1.5” inch in diameter whereas the entire plant spreads approximately 8” – 12” inches wide.
The mother rosette, known as the Hen, spreads in a circular pattern by growing horizontal stems in every direction.
These stems produce new rosettes called offsets or chicks.
Each new rosette becomes independent of the mother rosette by developing its own root system before detaching itself from the connecting stolon.
Cobweb houseleek is a relatively fast-growing succulent, but it is monocarpic which means it dies after flowering.
This, however, does not affect the overall beauty of the plant as there are several offsets to take the place of the dead rosettes and fill any gaps created.
Flowering and Fragrance
Sempervivum arachnoideum blooms excessively from mid to late summer when fancy pink flowers dominate over the short, fleshy foliage.
The Hen rosette produces a thick pinkish-red flowering stalk bearing a star-shaped flower with bright pink petals.
Some varieties produce pale yellow flowers instead of the usual pink blooms.
The starry flowers growing on tight rosettes measure about half an inch wide.
They grow in flat cymes on narrow stems reaching up to 5” inches high.
Light & Temperature
Like most hardy succulents, Sempervivums requires full sun but can perform well in partial shade as long as it receives sufficient sun exposure every day.
It is hardy in USDA hardiness zones 5 to 8 and grows best in the south and west-facing aspects.
Cobweb houseleek tolerates temperatures down to -25° degrees Fahrenheit (-32° C).
Watering and Feeding
The best practice for watering cobweb houseleek is to use the ‘soak and dry’ method.
Water the plant sufficiently and let the soil dry out completely before watering it again.
Sempervivum arachnoideum needs to be watered periodically in the flowering season and once in a while during the winter months.
The plant doesn’t need feeding, but repotting it in well-draining succulent potting soil containing compost mixed with a slow-release fertilizer ensures a long and healthy plant life.
Soil & Transplanting
Cobweb Houseleek is a low-maintenance but resilient succulent and performs well in a wide range of climates.
It is quick to adapt to local conditions, although it prefers well-drained and sandy soil types.
The ideal soil pH should be between 6 to 8.
Grooming and Maintenance
Once established, S. arachnoideum requires little to no maintenance.
Its fibrous root system holds the soil in place even when grown in vertical plantations.
At the end of the flowering season, the plant needs to be deadheaded.
The matured and spent rosettes and blooms should be carefully removed in order to make room for new ones to grow.
How To Propagate Cobweb Houseleek
Sempervivums are propagated by root offsets or seeds sown in spring.
It is not suitable for indoor plantation unless kept in a spot where it receives direct sunlight for at least 6 hours a day.
To propagate a new plant, gently remove the chick or baby rosette growing near the main plant (hen).
Carefully transfer it to the desired location and press the soil slightly to hold the baby rosette in place.
Cobweb Houseleek Pest or Disease Problems
Sempervivum arachnoideum is resistant to most of the common garden pests and diseases.
However, it is susceptible to rust, root rot, vine weevil, and leaf rot.
Cobweb houseleek is known to attract butterflies.
So, when planting these evergreen charmers, be prepared to welcome fluttering beauties in your garden.
Cobweb houseleek is safe to grow in homes and gardens.
Although it is not an edible plant, cobweb houseleek is not poisonous and will not cause any harm if ingested by pets or humans.
No toxicity has been reported for this succulent, but it is likely to cause nausea, vomiting, and diarrhea if ingested in a considerably large amount.
Sempervivum Arachnoideum Uses
Fleshy green rosettes adorned with white hair and distinct pink flowers; cobweb houseleek makes a fine addition to dry and stony places such as rock gardens, crevice gardens, and trough gardens.
Use it to decorate the cracks in dry stone walls and plant in front of garden beds and borders to give the place a touch of uniqueness.
Sempervivum arachnoideum provides good groundcover when planted closely together in large numbers.
This variety is a must-have for Mediterranean gardens and is perfect for edge plantation, be it in garden beds, troughs or even containers.
Plant cobweb houseleek separately in small clay pots placed on the windowsill for a dazzling display or use it to fill Sempervivum walls, mosaics, and topiary.
Pair it with other similar varieties to make a truly stunning succulent collection.