A succulent perennial of the Crassulaceae family, this variety is endemic to the mountains of Bulgaria, mainly the Pirin massif and surrounding ranges, where it colonizes rocks, cliffs, and sunny screes on various substrates, generally between 1,500 and 2,500 meters. It is named after Tsar Boris III of Bulgaria, a fervent amateur botanist who helped to popularize Balkan flora in the early 20th century.
It is one of the most densely hairy houseleeks. The rosettes, small to medium, 2 to 5 cm in diameter, are entirely covered with a dense, silky white hairiness that almost completely masks the green of the short, fleshy leaves. This woolly, almost unreal appearance, which evokes more of a high mountain desert plant than a succulent, is the most immediately striking feature of this variety. The clumps develop into dense and prolific cushions, by rapid multiplication of small daughter rosettes pressed close to each other.
The flowers, of a very particular pale yellow-green within the genus, are star-shaped and borne on 8 to 15 cm stems that are also hairy. In its natural habitat, its flowering extends from June to August. In cultivation, it generally blooms in June-July.
It is cultivated in full sun, in a very well-drained and poor substrate, with good protection against stagnant winter humidity, which is the main risk in cultivation. Perfectly hardy, it withstands intense cold under its natural snow cover. Cultivation in an alpine box or under light shelter in winter is often recommended in regions with wet winters.