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Houseleeks - Cultivation

06 Oct 2005

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Cultivation

Houseleeks
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References

Sempervivum species
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Houseleeks are found growing naturally in mountainous regions so they are adapted to withstand extremes of temperature. They do not like damp or shaded conditions so they should be grown in a well drained soil and exposed to full sunlight. A south facing bank or rockery is ideal.

In Britain most varieties will be found to be completely hardy although some types may require protection from excessive moisture in the winter. A simple transparent shelter of glass or plastic to keep off the worst of the winter rain is all that is usually required. Alternatively, a few offsets of the more delicate varieties can be potted up and over-wintered in a cold frame or unheated greenhouse.

Most enthusiasts grow houseleeks in pots but they can also be planted out in rockeries, walls, sink gardens and flower beds where they will soon develop into attractive cushions of rosettes. If small offsets are planted directly into the ground, care must be taken to prevent them from becoming covered over by other plants or weeds. It is probably best to grow offsets in pots and then plant them out into the garden when they are well established.

 

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Soil requirements

 

Houseleeks will grow in almost any type of soil provided that it is well drained and in a sunny position. For growing in containers we use a compost consisting of approximately 50% soil-less compost, 25% John Innes No.1 or No.2 and about 25% sharp sand for extra drainage. Although houseleeks grow naturally in poor soil most plants seem to grow best in a compost that contains plenty of nutrients. They can be given an occasional liquid feed with a general purpose fertiliser but best results are probably obtained by adding slow release fertiliser granules to the compost at the rate recommended for alpine plants. (Usually about 3gm/litre of compost.) A top dressing of horticultural grit around the neck of each plant provides an attractive background and prevents the plant from being splashed with mud during heavy rain.

In large containers, the bottom of the container can be filled with lumps of expanded polystyrene packing to save on compost and to reduce weight.

Although houseleeks will continue growing for many years in the same soil, they usually grow far better in fresh soil. 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. It is a good idea to re-pot plants each year and either detach some of the offsets for planting elsewhere or spread them out so that they have room to root and grow. Even plants growing in open ground benefit from being dug up and re-planted occasionally. They are remarkably tolerant of root damage and in fact they often seem to grow better if most of the old roots are removed when re-potting. This also provides an opportunity to detect and remove pests such as root mealy bugs or vine weevil larvae.

 

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Propagation

 

When growing healthily, rosettes will usually produce large numbers of offsets through the spring and summer. These 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 they have started rooting the young offsets can be pulled easily from the parent rosette and planted up separately. When planting young offsets it is best to break off the stolon at the base of the offset. This encourages the development of roots from the offset itself rather than from the end of the stolon.

By propagating from offsets the characteristics of the parent are preserved and this is the normal way of producing more plants. Most flowering rosettes produce fertile seed and seedlings can often be found growing among the parent plants. Hybridisation is very common so the resultant offspring will probably not look like the parent. To propagate a named variety it is essential to use offsets rather than seeds.

 

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Growing from seed

 

Houseleeks are monocarpic which means that after flowering, an individual rosette's life is over. Most flowers produce fertile seeds and these can be collected and grown easily but, since hybridization is very common, they rarely breed true to type.

Many enthusiasts like to grow plants from seed either to experiment with crossing different varieties, or in the hopes of developing new and attractive cultivars. Large numbers of seeds can be collected in the autumn by shaking the mature seed heads over a piece of white paper. The seeds can either be sown immediately and left to over-winter in the soil or they can be stored until the following spring.

Seeds should be scattered very lightly over the surface of sterilised seed compost then covered with a very thin sprinkling of sand. 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. Almost certainly there will be far too many seedlings germinating to grow them all but after a few months the most promising ones can be transplanted and grown on.

One of the fascinations of growing houseleeks is that anyone can raise and name new cultivars. This has, however, resulted in many cultivars that are very similar to each other. Before anyone decides to name a new variety they should have access to a large collection of cultivars in order to be certain that the new plant is distinct enough to warrant a new name.

The rules and regulations for the naming of new cultivars are set out in the International Code of Nomenclature for Cultivated Plants, Trehane, P., (1995).

 

 
 

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