Orostachys
Orostachys is a small genus of cold-hardy, rosette-forming succulents in the stonecrop family Crassulaceae, native to the mountains, steppes and rocky places of temperate and subarctic Asia. Its members are prized by growers for their tight, often powdery blue or grey rosettes, their habit of spreading into dense mats by way of slender runners, and the curious, tall, cone-like flower spikes that give the group common names such as dunce cap and Chinese dunce cap. Almost all species are monocarpic: an individual rosette flowers once, sets seed and then dies, leaving its offsets to carry on.
Description
Plants in Orostachys form low, compact rosettes of fleshy, closely packed leaves. Depending on the species the leaves may be spoon-shaped and rounded, narrow and pointed, or tipped with a small spine or cartilaginous bristle, and they are frequently coated in a chalky farina that lends the rosettes a soft blue-grey, silvery or lavender cast. Rosettes are typically small — a few centimetres across — and many species tighten into hard, ball-like buds through the cold, dry months, then open out and colour up in the growing season.
The most distinctive feature is the inflorescence. When a mature rosette is ready to bloom it elongates into a tall, tapering, densely flowered spike — narrowly conical or cylindrical — packed with many small, star-shaped flowers in white, cream, greenish, pink or reddish tones. Because flowering is monocarpic, that rosette does not survive the effort; well before this, though, the plant has usually thrown out numerous runners tipped with new plantlets, so a healthy clump simply carries on and spreads.
Distribution
The genus is Asian, ranging across a broad swathe of temperate and subarctic territory including Russia (Siberia and the Russian Far East), Mongolia, China, the Korean peninsula and Japan. Plants grow on rock outcrops, cliff ledges, gravelly slopes, old walls and thin stony soils, often in exposed sites with sharp drainage and full sun. Many populations endure genuinely harsh continental winters, and this natural cold-tolerance is a large part of the genus's appeal to gardeners in temperate climates.
Notable species
- Orostachys spinosa — a widespread, very hardy species forming tight rosettes of spine-tipped leaves that close into a firm ball in winter.
- Orostachys japonica — a cold-hardy species from Japan, Korea and China, grown for its neat rosettes and tall flowering spikes.
- Orostachys boehmeri — the plant often sold as dunce cap, with small blue-grey rosettes that offset freely on fine runners.
- Orostachys iwarenge — the Chinese dunce cap, valued for its powdery lavender-grey rosettes; a variegated form is popular in cultivation.
- Orostachys malacophylla — a broader-leaved, soft-textured species with pale flowers.
- Orostachys furusei — a compact, mat-forming species popular with collectors of miniature succulents.
The circumscription of Orostachys has been revised repeatedly, and some plants once placed here have been moved to related genera such as Hylotelephium and Meterostachys. Names in the trade can therefore be inconsistent; when in doubt, buy from a grower who labels carefully.
Cultivation
Orostachys are, on the whole, easy and undemanding given the two things they most want: sharp drainage and strong light. Grow them in a gritty, fast-draining, largely mineral mix, in a shallow pan or trough that suits their spreading habit, and give them the brightest position you can — full sun brings out the compact form and the best leaf colour, while too little light leaves rosettes loose, green and stretched. Water freely during the warm growing season once the mix has dried, then ease right off as the plants tighten down for winter; wet, stagnant soil in the cold is the main thing that kills them. See Watering and Repotting for general technique.
Many species are genuinely frost-hardy and can be grown outdoors year-round in temperate gardens — in rockeries, crevice gardens, tufa, walls and alpine troughs — provided the drainage is impeccable and winter wet is kept off the crowns. Because rosettes are monocarpic, expect the parent rosette to die after it flowers; this is normal, and the surrounding offsets quickly fill the gap.
Propagation and hobby notes
Propagation could hardly be simpler. The genus spreads naturally by runners and offsets, and the small plantlets that form at the ends of the stolons can be lifted once they have a few roots and potted on individually. Rosettes and even single leaves can also be rooted much as with other stonecrops (see Propagation — cuttings), and species come readily from seed — though, being monocarpic, a plant only sets seed as its final act.
For collectors, the appeal lies in the powdery rosettes, the seasonal shape-shifting from tight winter buds to open summer rosettes, and a handful of choice variegated and especially blue-grey selections (the variegated O. iwarenge among the best known). They make excellent subjects for shallow bonsai-style pans, mixed alpine troughs and hardy-succulent plantings alongside Sempervivum and hardy Sedum.
See also
- Sempervivum · Sedum · Hylotelephium — related hardy stonecrops
- Soil and potting mix · Watering · Repotting
- Propagation — offsets · Propagation — cuttings · Propagation — seed
- Pests and diseases