They’re cute, they’re collectible, and anyone can grow them
by WAYNE WINTERROWD photography by WEBB CHAPPELL
FOR SEVERAL YEARS, SUMMER AND WINTER, a pair of boots stood by the doorstep of a house in my village. Well worn and down at heel, they were nevertheless Sorels, the sturdy boots that are almost as familiar a symbol of Vermont as a can of maple syrup. These boots, which belonged to the owner of the local sawmill, had clearly seen hard wear. But before being discarded, they had found a second use: their rigid interiors were filled with earth, and from the top, from the laces, and even from the split toes, sempervivums spilled out. I am not sure this is the very best use I ever saw for such wonderful plants, but certainly it brought home the truth about them—they are both adorable in themselves and endlessly adaptable.
I doubt that my neighbor had ever heard the word sempervivum. It is, however, the most reassuring of all plant names, made up of two Latin words signifying “always living.” And indeed, only two things can kill sempervivums outright—shade and poor drainage. Given very little soil and a great deal of sun, colonies will continue their slow but steady increase as happily after the USDA Zone 4 winters of Vermont as in the year-round mildness of San Diego (Zone 10). Wherever they grow, they make compact rosettes in tight colonies, the smallest varieties being little gray buttons scarcely one-half inch wide, and the giants seldom achieving a diameter of five inches. Native to high elevations through central and southern Europe into Asia Minor, they are essentially rock plants, growing in thin deposits of gravelly scree or finding a toehold in fissures of granite cliffs. But as rock plants, they are unusual—perhaps unique—in that their cultivation is child’s play, but their charm is hardly lost on the most dedicated members of the North American Rock Garden Society.
A BOTANICAL MUDDLE
Though universally pleasing to gardeners, sempervivums are a cause for serious indigestion among botanists, for the genus is as confused as the plants are confusing. It consists of about 40 species, though for three reasons no one can really be sure of the number. First, all species show variants in the wild. Second, plants of the same species will differ markedly in appearance according to the conditions under which they are grown. And finally, all are dreadfully promiscuous, freely intercrossing among themselves and with their parents. The permutations are therefore almost infinite. Even a bit of vegetable crusting isolated high on a Swiss mountainside might actually consist of two species and a swarm of offspring, each resembling one or the other parent, or each other, or nobody at all. And there are hybrids occurring naturally in gardens or by deliberate intervention, a welter that caused T.H. Everett, in his great garden encyclopedia, to cut through the Gordian knot of nomenclature by remarking bluntly, “The wise gardener will pick the sorts that he likes and use them in his garden for what they are, and not for what they are called….rsquo;
Inevitably, however, this very plethora of variations, so frustrating to the botanist, is a joy to gardeners, who seem born to collect one of this and one of that and one of the other. Once you own two forms of sempervivums (or semps, as they are called), you’ll soon acquire a third, and then perhaps a dozen, submitting happily to the disease someone has called “semperviviphilia.” After all, propagation is easy, cultural requirements are clear and undemanding, and plants will, well, live forever. Any chance encounter on a trip should therefore justify tucking a wayward chick in one’s pocket, sure in the knowledge that it will survive once home.
Despite the nomenclatural anxieties, however, a convenient broad distinction can be made between two clear species of sempervivums. Most plants on the market derive either from Sempervivum tectorum, the true houseleek (tectorum means growing on roofs), or from S. arachnoideum (from the Greek arachne, meaning spider), the “cobwebby houseleek,” so called because its tiny rosettes are netted over with threads of silver. Though the two species are closely related, they differ significantly in appearance. True houseleeks tend to be larger, sometimes to as much as six inches across, fleshier, and more open in their construction. Even when they seem colored a characteristic, uniform, dull olive green, there will be a shading of bronze toward the tips of the leaves, or even deep metallic or rusty colors diffused throughout.
What’s In a Name?
The two principal common names for sempervivum-hens and chickens and houseleeks-endear them to gardeners and non-gardeners alike. Hens and chickens describes the growth habit of the plants, where every mature individual produces miniature versions of itself, either growing close beside its perfectly crafted rosette of leaves, or on corky, threadlike stolons an inch or two long. Houseleek is of less clear application, for no species resembles that garden vegetable. It is true that the succulent leaves have been gathered for salads, but the name, which descends from medieval English, more probably refers to the bloomy, gray-green color that some sempervivums share with the common leek, Allium porrum. -W.W.
By contrast, the cobwebby sorts are generally smaller, sometimes mere buttons one-half inch across, more rounded or ball-like in shape, and typically celadon green, though their characteristic webbing gives them a silvery appearance. To these two dominate species may be added a third, S. calcareum, which repeats the fleshy, open rosettes of S. tectorum, but, in its selections and hybrids, possesses some of the most subtle colorations in the genus, of plum and bronze and fuchsia pink.
A table at a garden center containing a really good selection of sempervivums may display a range from the tightest buttons to the most open saucers, always with leaves arranged in each rosette with mathematical precision, chicks crowded close under their mother or questing into neighboring pots. Color may be anything from grass green through split-pea soup to celadon, porcelain gray, or olive drab, and near to black. Often there will be haunting shadings of russet pear or bloomy plum or grape, blends of pink and gray, or individual leaves tipped in mahogany or shadowed in violet. Then there may be hairs, densely webbing each rosette and silvering it over like a bit of discarded fleece, or edging each leaf like new frost. Simply choose what you like best—if you can—and then get home fast.
For these are plants that will not fail to grow for you. Confusing and uncertain as their pedigrees may be, culture is simplicity itself. Their only requirements are for a gritty, perfectly drained soil and baking sun. Indeed, their preferred mountain habitats, where soil is thin and summer sun abundant, give the vital clues to their needs. It also suggests their most exciting uses in gardens, for they require only a little soil, even so little as a cupful, settled in the hollow of a rock. They relish stonework of all kinds, making glorious the faces of old decayed walls and even giving to new ones a look of settled age with surprising rapidity. No other plant is as easy to establish in a wall, for a narrow crevice can be packed with fibrous loam or decomposed sod, and a nursery-grown plant freed of its four-inch pot and squeezed gently in, so that its rosettes of growth are even with the faces of the surrounding stone. Even a single rosette can be inserted in a fissure with a little soil behind, perhaps anchored with a couple of pebbles. It will soon occupy the space it has and then colonize the adjoining stones.
‘They relish stonework of all kinds, making glorious the faces of old decayed walls…rsquo;
Though sempervivums and walls seem made for one another, colonies may be equally effective along the edges of gravel drives or walks, in the cracks of concrete pavement, even on the roof, if it happens to be of tile or stone. Almost any container will support a colony, or even a collection, provided it is perfectly drained. For all-year effects in cold gardens and for chilly urban roof gardens, semps are perfect, for their gelatinous leaves seem to possess natural antifreeze, preventing them from bursting apart or turning to mush even after subzero winter lows. They are one of a very few plants that may be expected both to live and to be attractive in urns and pots in gardens that experience very cold winters. They may glorify an old, chipped dish pan, a flat rock with the barest hollow to hold soil, a terra-cotta chimney tile, or a weathered cinder block. They’ll even do in an old pair of boots, if you happen to have them. H
For sources of sempervivums, turn to page 76.
Sempervivums have a long and distinguished history in Western gardens. The Roman natural historian Pliny the Elder is the first to mention them by that name, recording the belief that plants growing on roofs deflected lightning and prevented fires. To scholars in the Middle Ages, this belief made entire sense; why else would they choose to grow in such unlikely places? So, in the 9th century, the Holy Roman emperor Charlemagne, ever concerned with the well-being of his subjects, issued an edict that sempervivums be established on every house roof. It naturally followed that any plant possessed of unusual capacities must be medicinally valuable, and so medieval physicians prescribed teas of sempervivums to cure sores of the mouth, irritated throats, bronchitis, and all diseases of “heat” or fever. The mucilaginous tissue of the inner leaves was also believed to soothe burns and bee stings, as perhaps it does. –W.W.