This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
The Houseleeks are an easily grown group of plants with fleshy leaves in dense rosettes, and are valuable for old walls, roofs, rockeries, etc, in dry soil or old mortar rubble. The Common Houseleek (S. tectorum) is sold freely, and so is the Spider-web Houseleek (S. arachnoideum), a Pyrenean species with cobwebby hairs over the leaves. S. calcareum (erroneously called californicum) and S. montanum are also excellent. There are many others not so well known (see Practical Guide to Garden Plants, pp. 441-3) that are as easily grown, and might be more generally cultivated. They are readily propagated by separating the young plants or offsets from the old ones, and replanting in autumn or spring.