Sempervivum by Post

Sempervivum are excellent plants for sinks and troughs, either grown with other small alpines as part of a miniature landscape, or planted as a collection of several different Sempervivums. Place contrasting colours and various rosette sizes together for the best effect, or plant in rows with pieces of slate between each type to give a striped effect. To grow in strawberry pots, plant one variety in each hole, using some that produce offsets on long runners to hang down.

Sempervivums will grow in the most unlikely containers, with only shallow soil in some cases . Try them in the hollow pockets of concrete building blocks, the ends of pieces of piping, old logs, even bricks and pantiles.

If grown in the ground, they require a well-drained spot in full sun where they will not be covered or overhung by other plants. Gravel gardens or narrow beds alongside the house are ideal, where they will form large attractive patches of rosettes. They are also happy in rockeries, raised beds and walls.

Sempervivums require a gritty well drained compost. Equal parts of peat based compost, John Innes No 1 and grit is an ideal mixture. In a deep container, such as a sink, a layer of coarse grit or gravel in the base is also beneficial.

Once planted topdress the container with sharp grit gently pushing it under the rosettes - this will help to deter slugs. Water the new plants to settle the compost, and then subsequently water very sparingly keeping the compost just moist.

Flowers are often borne in summer, on tall stems emerging from the older rosettes. They are usually reddish brown or rose in colour, sometimes yellow, starry shaped and clustered near the top of the stem. Although the main flowering rosette dies, numerous offsets are produced around each rosette. These are either clustered closely around the base or borne on long runners. Let the old flowering stems dry off, so that they can then be easily pulled away. Fill in the gap with grit and the newer rosettes and offsets will gradually grow into it.

Sempervivums benefit from a light feed of a fertilizer such as pelleted chicken manure twice a year, but care should be taken to avoid getting the pellets on the rosettes.

Although most Sempervivums are completely frost hardy and will stand outside all winter, those in pots will be happier under cover in a cold greenhouse or cool conservatory, where they will provide winter interest. Keep them on the dry side over winter.

To get the best colours from the rosettes the plants should be grown in full sun. The colours tend to fade in the winter but the brilliance will return with the brighter spring and summer weather. They show a range of subtle and bright colours, including apple green, lime green, deep red, darkest mahogany and soft mauve.

Notice that the rosette sizes and shapes vary as well as the colours. Even the individual leaf shapes are different, some being fat and globular, some short and pointed, others long and tapering. They may be matt or shiny, covered in short soft down or have longer hairs along the leaf margins. Others have a cobweb of hairs over the whole surface that connects the leaf tips. Rosette sizes range from tiny huddled ones with minute leaves up to very large imposing types where a single rosette can measure 10cm or more across.