About the genus
The name Sempervivum is derived from Latin meaning ‘always alive’ which indicates the hardiness of this group of plants. They are often classed as ‘Alpines’ and are found in many European mountain ranges including the Pyrenees, Dolomites, Caucasus, and Alps. Their natural habitat means they are exposed to full sun, heavy rainfall, sub-zero temperatures and snow coverage during the year. Thus, in cultivation they need an outdoor location, very good drainage, full sun and just moderate feeding. Their steep, rocky habitats mean that when exposed to seasonal deluges the water drains quickly and the plants do not sit in water for extended periods.
There are approximately 50 accepted species and upwards of 3,500 cultivars. Some of these are sufficiently distinctive to be confidently identifiable, but because of their tendency to change appearance during the year, depending on the weather during the spring and summer, identifying unnamed individual specimens can be challenging. Their creamy-white or pink flowers develop on tall stems and are very attractive to bees.
How to grow them
Sempervivums propagate vegetatively in spring by stolons. These each develop a single new rosette at the tip which quickly roots down to form a new plant. The stolons are typically quite rugged and can persist for a few years. Once the new rosette has developed roots it can be detached from its parent and potted up separately to form a new plant. This is the only sure way to ensure thecontinuity of a species or cultivar. The stolons may be short or long, and it is quite easy for plants to colonise neighbouring pots!
Sempervivums are monocarpic so rosettes that flower will die (after setting seed). Normally, established plants produce many pups which do not all flower at the same time, so avoiding the plant ‘flowering itself to death’.
Excellent drainage is key to successful cultivation. A mix of approximately 50:50 horticultural grit and compost in shallow terracotta pots and a sunny, outdoor location all year is ideal. The variety of compost is not critical so long as good drainage is maintained. Top dressing with grit, tucked under the rosette leaves, will help avoid premature rot of the outer leaves. Minimal feeding is necessary, but a single dose of dilute tomato feed in the spring to replenish the nutrients washed out by winter rains can be beneficial.
Sempervivums have few ‘enemies’, the worst being poor drainage. Weeds in the pot may have lengthy roots clogging the drainage holes, retaining water and causing the leaves to rot. Dying leaves, even in dry conditions and especially in the more succulent varieties, may indicate the presence of a relatively new pest, the Sempervivum leaf miner, a species of hover fly whose larvae burrow into the succulent leaves and eat them from the inside. Careful inspection will find the larvae, which can be removed and destroyed. Spraying with a suitable pesticide may provide some control.
Vine weevil is the other major pest, whose fat, creamy white grubs eat the roots and sometimes the centre of the rosette. De-potting and inspecting the compost will find the grubs. Affected rosettes will often re-root and grow again if placed on the compost surface.
Text and photos: David Sheppard
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