Sempervivum ‘Onyx’

Sempervivum 'Onyx' (Sempervivum 'Onyx') is a hens and chicks succulent grown for rosettes so dark they read as near black. Each rosette sits about 10cm high and the clump widens to roughly 30cm as it rings itself with offsets. It is the succulent for a cold garden: genuinely frost hardy, drought tolerant, content in poor soil and not toxic to cats or dogs.

Why you'll love it

• It handles real cold. An alpine by origin, so tableland and southern gardens that kill most succulents suit it perfectly.
• Pet safe. Hens and chicks are not toxic to cats or dogs, so it can sit at ground level without a second thought.
• It propagates itself. Each rosette rings itself with offsets that root where they land, so one plant becomes a colony.
• Poor soil is an advantage. Gravel, a wall crevice or sandy mix all produce tighter, darker rosettes than good soil does.

Where it works best

Rockeries and crevices. Its natural habit is a rock ledge, so gravel gardens, dry stone walls and pockets between stones give it exactly the drainage it wants.

Groundcover and edging. Plant 20cm apart for a dense mat of rosettes along a path edge or across a shallow bed, and expect it to close over in two seasons.

Pots and balconies. A wide shallow bowl of gritty mix suits the spreading habit, and it is small enough for a courtyard table.

Growing sempervivum in Australia

Position and climate. Full sun, in cool temperate, warm temperate, Mediterranean and arid or semi-arid gardens. Cold is not the limit here, humidity is: in the humid subtropics and tropics a wet summer rots the crowns, so gardeners there should keep it potted under eaves.

Soil. Sharp drainage above all else. Use a gritty cactus and succulent mix, or open garden soil up with coarse sand and gravel, and plant on a slight rise.

Water and feed. Very little of either. Soak it, then let the soil dry right through: every two to three weeks in warm weather and almost never in winter. Rich feeding only produces soft, loose rosettes.

Pruning and grooming. Pull away shrivelled outer leaves, and pick off any rosette that has flowered. Each rosette flowers once, lifts pink blooms on a short stem, then dies and is replaced by its own offsets.

What to expect when it arrives

Sempervivum 'Onyx' is supplied as tube stock, a single young rosette rather than an established clump. Pot it up or plant it out straight away, and expect the first ring of offsets within a season and a filled 200mm bowl within two.

Succulents travel well, though hold off watering for a week after arrival so any handling damage seals over. The colour deepens with sun and cold, so a greenish plant darkens once it is outside. Delivered Australia wide, delivery from $29.95, and every plant carries our 30 day healthy plant guarantee.

Plant care guides and related reading

• Plants that thrive in poor soil
• Browse the full succulent range
• Plants for rockeries and gravel gardens
• Plants that are safe around pets

Common questions

Why did one of my rosettes die after flowering?

That is normal and not a fault. Each rosette flowers once and then dies, while the offsets it produced take its place, so the clump carries on.

Will it grow in a humid climate?

It struggles. Humid wet summers rot the crown, so in the subtropics and tropics grow it in a shallow pot under an eave, out of summer rain.

How much frost can it take?

A great deal. It is alpine in origin and hard frost does not trouble established plants, which is why it suits tableland and cold southern gardens.

How do I make more plants?

Detach the offsets once they have a few roots of their own and press them into gritty mix. They need no rooting hormone and very little water while they take.