Hens and chicks are so named because of the way they reproduce vegetatively. The “mother hen” (the main rosette) is surrounded by small replicas of herself, “chicks,” which are often borne on the ends of long, trailing stems (stolons). The chicks can either be left to root around the main plant, where they will form a cushion of rosettes, or detached and grown separately.
After two or three years, the mother hen will produce a flower spike of up to 15 centimetres high with white or pink flowers. (This stem can be easily pulled away if allowed to dry up.) The main flowering rosette will then die, but the chicks will eventually become mother hens, producing their own chicks.
Semps hardy to Canada are generally considered trouble-free, long-lived plants without major pests or disease problems. Semps grown indoors, however, are susceptible to mealy bugs.
Some stunning cultivars
There are so many species and hybrids that cultivars are often not labelled. However, there are two main species:
Sempervivum arachnoideum Also known as the spiderweb or cobweb houseleek, it forms a low rosette that spreads up to 25 centimetres wide and becomes densely covered with cobweb-like, white threads. The plant develops bright pink to rose red flowers in early summer and is hardy to Zone 5. Examples include S. a. ‘Canada Kate', whose velvety green and red leaves have tiny tufts of hair on the tip, and S. a. ‘Cobweb Capers', whose rich green leaves are tipped with white hair.
Sempervivum tectorum Commonly known as houseleek or roof houseleek, its spoon-shaped, bright- to mid-green leaves form rosettes up to 7.5 centimetres high. During midsummer it bears purple flowers on 15- to 23-centimetre-high stems and is hardy to Zone 4. Examples include S. t. ‘Donar Rose', a medium-sized variety with green leaves washed with rose, while S. t. ‘Purple Beauty' has blue-green leaves shaded and tipped in red.
The botanical name Sempervivum means “always alive.” Even rosettes left dry and without soil for several months will usually survive and grow rapidly as soon as suitable conditions are provided.
Sempervivum leaves are succulent and contain water. In Britain they are known as houseleeks because the Welsh used to plant them in thatched roofs to help prevent fire damage. This was also a common practice throughout much of Europe. Offshoots were planted, with a minuscule amount of soil, into gaps between thatching, lumber or roof tiles.