Cobweb Houseleek (Sempervivum arachnoideum)
From the mountainous areas of Southern Europe comes the Cobweb Houseleek, one of the most attractive of the genus. This prostrate-growing succulent is ideal for patio tubs and makes a good companion for many other alpines; it will not tolerate over-watering, so any container used should be tucked under the eaves of the house for. Each tiny leaf rosette is no more than 1.5cm (3/4in) wide and made up of about 50 or more wedge-shaped leaves. Although grown mostly for its foliage, the plant produces bright red, star-shaped flowers on 10cm (4in) stems in June and July. In Winter, the outer tips of each rosette take on a reddish tinge. With age, offsets appear and should be used as replacements when the main plant dies off after flowering.
This frost-hardy plant tolerates temperatures down to 5°C (23°F), as long as they are not combined with very moistor .
Position in direct sun or light shade. During very hot weather, containers of alpine plants, such as this, benefit from being moved out of the sun’s direct rays.
This tough little plant can easily be killed by over-watering: it needs a very free-draining compost to carry any water rapidly away from the root system. From Spring to Autumn, water well, then allow the compost to become dry to the touch before giving another thorough watering. In Winter, give just enough to prevent the plant from shrivelling.
S. arachnoideum needs no additional humidity; excess moisture will tend to settle among the closely-packed rosettes and create an ideal environment for rot.
Don’t feed this plant; neglect and starvation are the keys to success with the Cobweb Houseleek.
Grow in a low-nutrient compost; too much food will interfere with the plant’s intrinsic growth pattern and may result in limp growth. Use a compost intended for alpines, or mix your own by adding up to a third by volume of horticultural grit to the mix. Repotting should only be required if the parent plant dies and the offsets are used as replacements.
A shallow, free-draining bowl makes a suitable container and is ideal for the prostrate, spreading habit of the Cobweb Houseleek.
Cultural problems: Fewtrouble this plant; any problems are more likely to be cultural than pest related. Too much water will lead to rot, while too much heat and food will cause limp and inappropriate growth.