How to cultivate Sempervivums


getting ready for their BIG debut at this weekend’s Cultivate tradeshow in Ohio! I’ve been growing Sempervivums since I was 5 years old and they’re still captivating to me with their wide variety of colors and forms.

Sempervivums are available in many forms and colours, green through browns, yellow, orange, pink and red although they need to be grown in full sun to fully exhibit the different colours. Out of full sun many cultivars tend to end up as a similar green colour.

Leaves may be glossy or matt, in some cases with a waxy bloom or with downy hairs. Mature rosettes can be from half an inch to 6 inches in diameter and some species/cultivars have hairy rosettes. Small silver-coloured hairs may occur along leaf margins with a more pronounced clump of hairs at the leaf tip. In some cultivars these hairs are long enough to produce a pronounced cobweb effect. The numerous forms available is one of the main attractions of a collection of Sempervivums.

Traditional Uses: Sempervivums were considered sacred to Jupiter in Roman and Thor in Nordic mythology. The flower was said to resemble the beard of the God.
Jovibarba (L.) Iovis barbam = Jupiter’s Beard

In some places Sempervivums are traditionally grown on roofs between thatching, tiles or timber. In ancient times, this was thought to guard against thunderbolts, storms and sorcery and ensure the prosperity of the occupants. Perhaps corona discharge from the pointed leaves could reduce the local electrical field strength and thus the chance of a direct lightning stroke. A firm in Germany exports Sempervivums as rolled up carpets of roofing material, exhibited at the 2003 Chelsea Flower Show.

Traditional medicinal uses described by Pliny the Elder (23 – 79 AD) in his Naturalis Historiae include use of the juice from crushed Sempervivum leaves to treat skin complaints such as burns, scalds, corns, calluses, warts, ringworm, shingles (localized infection with the chickenpox virus), insect stings shingles, itching and burning of the eyes, and earache. Discorides (40 – 90 AD) wrote in his Materia Medica that Sempervivum leaves crushed with wine would eliminate intestinal worms and flukes. The Romans also considered Sempervivum juice to be useful against caterpillar infestation of crops.
Medicinal use of these plants is not recommended here.

Cultivation: Most Sempervivums are quite frost resistant and very easy to grow outside in rock gardens, planters and troughs. A tray or planter of different coloured Sempervivums can look very decorative and of course has the advantage of not taking up indoor growing space. Sempervivums also do well in cracks in dry stone walls, on tufa and in rock gardens. They dislike damp conditions and prefer full sun, but are otherwise undemanding. They should be planted in a shallow gritty, free-draining compost incorporating 25 – 50 percent sharp sand and grit, with a top dressing of grit between plants.

The only snag with Sempervivum plantings is that this genus is monocarpic i.e. each rosette can only ever flower once and then dies. The dead plant leaves a hole in a clump, which could be a problem with a roof carpet. The dead rosette should be carefully removed and the hole filled with gritty compost. Most species / cultivars produce lots of offsets which usually make up for any losses after flowering. Rosularias may rest in mid-summer.