Sempervivella alba

Sempervivella alba (syn. Rosularia alba, Sempervivum album)

Think of a houseleek (Sempervivum) and reduce it to a quarter of its size and you have Sempervivella alba. Its a little gem of a plant which, like its larger brethren is extremely easy to grow and propagate. Yet it is not often seen.

As the illustrations show, Sempervivella alba forms neat, low domed hummocks or mats of tightly packed rosettes. These are 2-4 cm across, composed of oblong, succulent, pale green hairy leaves, often tinged red in hot spells of weather. Late in the season (July to early September in the UK) the rosettes produce self-rooting offsets on thread-like stolons. At the same time each mature rosette produces a cluster (cyme) of glistening creamy-white flowers. These open sequentially and each remains in good condition for several weeks. The wild home of Sempervivella alba is on the lower slopes of hills from Kashmir south-eastwards to Himachal Pradesh.

Cultivation

Like all its kin, this is an extremely easy plant to cultivate given one proviso – perfect drainage. Waterlogging, or even permanently moist ground is anathema, while ‘thin’ sandy soils containing little nitrogen are perfect. Sempervivella looks best in a crevice in a trough or other container where it will thrive unattended for years. An occasional weak feed is in order, but nothing more.

Propagation of Sempervivella alba

Seed is set but is dust-like and will take a year or two to produce a decent plant. Much better to use the plant’s own principal means of increase, the offsets that it produces so freely. These can be detached at any time, but early autumn is probably best. If they are already rooting into the soil around their parent, lift carefully with a fork and snip through the stolon. If not, simply cut them off and root them in a pot of gritty compost. Or, if you are prepared for disappointments you can prick them out directly where you wish them to grow. Either way, water until they are established but thereafter only during extreme drought conditions.