Adopt-a-Genus: Sempervivum
by Judy Wall

Sempervivums are hardy alpine succulents from the family Crassulaceae, commonly known as 'Hens & Chicks' or 'Houseleeks', which are native to the mountains of Europe, the Middle East and Central Asia. There are around 50 species and thousands of different varieties. The International Register of Sempervivum cultivars contains about a thousand named varieties and many more are grown from seed by individuals doing their own crossing without identification. Therefore it is extremely difficult to ensure, when purchasing plants, that they are properly named.

Most people grow Sempervivums (Latin for always living) for their succulent rosettes of many colours, shapes, sizes and clumping characteristics, rather than for their flowers. The colours range from red, green, burgundy, gray, lavender, pink, yellow, black, etc., through to many colour combinations, such as red on the inside with green on the tips and vice versa. The leaves may be dull or glossy, or covered with soft down or longer hairs. The shapes of the rosettes vary from being elongated on one side, to very tight and rounded or more open and flat. How rosettes and their offsets clump and multiply also varies, some being very tight together and others more mounding. Different varieties have different sizes of rosette: very small - 1 cm or less, small - 1 cm to 3 cm, medium - 3 cm to 6 cm, large - 6 cm to 10 cm, very large - 10 cm or more. S. arachnoideum (photo on the left) varieties have a very interesting “cobwebbing” of silver hairs on top of their rosettes.

Pay close attention to your semps. The plants change colour throughout the year. They are very colourful in the spring once out of dormancy. The colour then fades during the heat of summer but comes alive again come the cooler fall weather.

These plants reproduce vegetatively with offsets grown on several stolons produced around the base of the parent rosette. Each offset will develop roots of its own and become independent of the parent plant as the connecting stolon withers. Remove the offsets when root development has begun and replant. This method preserves the characteristics of a named cultivar.

The rosettes that do flower contain seeds that can be easily collected and grown. Seedlings are unlikely to breed true to their parentage, thus providing you an opportunity to experiment and see what unique variations you can grow. When a rosette flowers, that’s the end for that particular rosette. If you do not like the flower, simply remove this particular rosette.

Plants of the Jovibarba and Rosularia genera can be confused with the semps. They are most easily distinguished by their flowers. Semps have star-shaped, usually pink flowers with 8-16 petals, Jovibarba flowers are yellow, more bell-like and have 6 petals, and Rosularia flowers are usually cream or pale yellow, open, and have 6 to 8 petals.

Sempervivums are hardy to Canadian Zone 2/USDA 1, and fairly easy to grow as they tolerate a large range of soil conditions, from regular garden loam to leaner scree conditions. The key is good drainage. Winter wet or wet roots are a killer. They do well in full sun to part shade. They are also great plants for containers such as hypertufa troughs. Semps are so versatile that once you have a collection of them, you can take your extras and create interesting containers/trays for enjoyment indoors over the winter or make a living wreath.