Sempervivum


 

Common names: House leeks, Hens and Chicks


Overview:

Sempervivum is latin term for "always living" which is a reference to the fact that they can tolerate extreme temperatures and drought.

The common name 'House Leek' goes back to ancient times when it was grown on roofs to supposedly guard against thunderbolts, storms and sorcery and ensure the prosperity of the occupants.

Legend also states that Sempervivums were considered sacred to Jupiter as the flowers were said to resemble his beard.


The species are alpine succulents that originate from the mountainous regions of central and southern Europe where they are found at over 3000 feet above sea level, meaning they are well adapted to withstanding extremes of temperature.

There are now around 50 species and over 3000 named cultivars with a wide range of rosette sizes, forms and colours, e.g. green, brown, yellow, orange, pink and red.

The rosettes can spread from 12mm (½") to 150mm (6") across, and the leaves may be glossy or matt, and in some cases they may have a waxy bloom or downy hairs.


 
Different coloured / shaped Rosettes

Each rosette is a separate monocarpic plant, meaning it flowers once and then dies, but is soon replaced by other new rosettes (offsets).

These offsets can be separated and planted up, and will then grow into new clumps.

The star-shaped flowers can have 8 - 16 petals and can be pink, red or pale-yellow.


 
Different coloured / shaped flower buds

 
Different coloured / shaped flower heads

Position can have a bearing on the final colour, for example; plants grown in full sun will give the greatest variation in colour.

Conversely, plants grown in shade tend to end up in various shades of green, however they do not like shaded conditions particularlyif they are very damp.


In the UK most varieties are completely hardy although some types may require protection from excessive moisture in the winter.

As an insurance it can be advantageous to take a few offsets of the more delicate varieties prior to the onset of winter and pot them up up and over-winter them in a cold frame or unheated greenhouse.


The frost resistance of these plants make them a plant well suited to growing outdoors in rock gardens, planters,troughs and in the cracks of dry stone walling.

Alternatively they can be potted up into pots for displaying indoors.

It is thought that many of these attributes are the main attractions as to why so many people collect Sempervivums.


Cultivation:


Sempervivums will grow in almost any type of soil provided that it is well drained and in a sunny position.

In the wild Sempervivums grow naturally in poor soil, however many varieties seem to grow better in a compost that contains plenty of nutrients.

Nutrients can be supplied by applying an occasional balanced liquid feed, or adding a granular slow release fertiliser at a rate of 3gm of fertiliser to 1 litre of the compost.

A top dressing of horticultural grit around the neck of each plant provides a good drainage layer and apart from it being quite attractive, it is reminiscent of the scree beds found in their natural environment.


Containerised Plants:


Shallow containers are often considered to give the best results but filling the lower level of a deep pot with gravel or crushed polystyrene will prove equally as good.

Use a compost mix consisting of approximately 50% soil-less compost, 25% John Innes No.1 or 2 and 25% sharp sand for extra drainage.

Containerised Collection

After a year or two most plants will have produced a large number of offsets and there may be unsightly gaps in the clump where mature rosettes have flowered and died.


Shallow containers are often considered to give the best results but filling the lower level of a deep pot with gravel or crushed polystyrene will prove equally as good.

Use a compost mix consisting of approximately 50% soil-less compost, 25% John Innes No.1 or 2 and 25% sharp sand for extra drainage.


To overcome this problem re-pot plants and either detach some of the offsets for planting elsewhere or spread them out so that they have more room to root and grow.


Sempervivums are remarkably tolerant of root damage, in fact they often seem to grow better if most of the old roots are trimmed / removed when re-potting.

Prior to Splitting
After Splitting

This re-potting exercise also provides an opportunity to detect and remove pests such as root mealy bugs or vine weevil larvae.


Propagation:


To propagate a named variety it is essential to use offsets rather than seeds, that is; propagating from offsets ensures that the characteristics of the parent are preserved.

A word of warning; most flowering rosettes produce fertile seed and seedlings can often be found growing among the parent plants, so care must be taken to ensure that you are taking an offset from the parent plant rather than a self seeded seedling.

That is; hybridisation is very common so the resultant seedling may not look like the parent.


In spring and summer rosettes produce large numbers of offsets.

If these offsetts are left to their own resources they will send down roots of their own and eventually become detached from the parent rosette when the stolon withers, or when the parent plant dies after flowering.

Once the offsets have started rooting pull them away from the parent plant and break off the stolon as this encourages the development of roots from the offset itself rather than from the end of the stolon.


Seed Collection:


Many enthusiasts like to grow plants from seed either to experiment with crossing different varieties (hybridizing), or in the hopes of developing new and attractive cultivars.

In autumn flowering plants often produce a star-shaped fruit containing fertile seeds which can be easily be collected.

The fruit should be allowed to dry, before crushing it then separating the debris from the seed.


Alternatively; shake the mature seed heads over a piece of white paper and place them in a seed packet.

The seeds can either be sown immediately and left to stratify outdoors in the soil, or they can be stored until the following spring.


Seed Sowing


Seeds should be scattered very lightly over the surface of sterilised seed compost then covered with a very thin sprinkling of sand.

If using stored or commercially purchased seeds; stratify the seeds after sowing by chilling in the fridge at 4 deg C for a few weeks.

Alternatively sow the seeds in a pot/tray and place outdoors during the winter to stratify.

Either of these methods will greatly enhance germination.

The first sign of germination is the appearance of a pair of tiny succulent seed leaves (cotyledons) and this is soon followed by the development of the new rosette.


New Varieties:


Seed sowing is one of the fascinations of growing Sempervivums as anyone can raise and name new cultivars.

In terms of establishing if you have a bred a new variety, or indeed naming the variety you will have to check the rules and regulations for the naming of new cultivars.

These are set out in the International Code of Nomenclature for Cultivated Plants, Trehane, P., (1995).

Pekinese
Rosie

After germination you will almost certainly find that you have far too many seedlings to grow them all on.

It is at this stage you will have to decide as to which plants you wish to keep and grow on, one way of doing this is to allow the seedlings to grow on for two or three months then have a cull.

More than likely many of the seedlings will look very similar and it is probably best to discard these and only save the seedlings that look a little out of the ordinary, as these are the ones that you are most likely going to get a new cultivar from.



Top of the Page