Houseleek: winter hardiness, propagation & flowering time of Sempervivum

Even in ancient times, a houseleek on the roof protects against lightning. How much truth there is in it, is not proven, but houseleeks are low-maintenance, extremely decorative plants, for example, for stone and front gardens.

With the species-rich genus of houseleeks, the botanical name says it all: Sempervivum stands for “always alive” and refers to the fact that houseleeks are very robust, undemanding plants. Houseleeks need a nutrient-poor, lean soil, in addition, neither drought nor heat or cold harm them. For this reason, houseleeks are among our top 10 low-maintenance plants. Read on to find out more on the appearance and flowering of houseleeks, as well as answering the question of how hardy Sempervivum is, and instructions for propagating houseleeks.

Houseleek: flowering time, origin and characteristics

Contrary to the belief that succulents are found primarily in deserts and warm regions, the natural range of the houseleek is in the mountains of Europe, extending from the Caucasus to the Sierras in Spain. As far as parts of Asia and North Africa, the houseleek is widespread. There Sempervivum likes to colonise sunny stone slopes and rocks.

The houseleeks represent a genus within the family Crassulaceae, which includes about 60 species. Some estimates suggest that there are close to 7000 cultivars. Accordingly, the choice in the trade is huge. Therefore, in a separate article, we will go into more detail about different species and varieties of houseleek, which are well suited for the garden.

Houseleeks are hardy evergreen perennial plants that grow as clumps. They form leaf rosettes with a species-dependent diameter between 1 and 20 cm. This particular appearance and the fact that Houseleeks are found mainly in stony areas, have also earned them the name rock rose. The leaves are thick and fleshy, which is typical for leaf succulents, as the leaves serve as water reservoirs.

Only from the age of three years Houseleeks bloom in the flowering period from May to August. But at the same time this means their end, because after flowering stone roses die. Before flowering, the shoot begins to stretch until the flowerhead usually rises between 7 and 20 cm in height, depending on the species. Based on the appearance of the flower, the genus Sempervivum is divided into two sections. Section Jovibarba includes only two species, which are characterised by an almost bell-shaped flower. The flowers of houseleeks in the much larger section Sempervivum, on the other hand, are usually spread in a star shape and have significantly more petals.

What is the difference between houseleek and succulents? Succulents are plants that store water in their organs – stem, leaf, or root(neck) – and are thus adapted to extreme drought. Houseleeks are also characterised by this growth habit: They store water in their thickened leaves. So, there is no concrete difference between succulents and houseleeks, rather houseleeks represent an example of succulents.

Are houseleeks hardy?

All species of the genus Sempervivum are hardy. Many Houseleeks are classified as winter hardiness zone 6. This means that these houseleek species are hardy to temperatures between – 18 °C and – 22 °C. Some species can even tolerate temperatures as low as – 34 °C. Therefore, the overwintering of houseleeks is possible in the vast majority of regions without any problems.

Only when wintering houseleeks in a pot should you be a little careful. In a container, the roots are less protected and so it may happen that basically hardy stone roses yet frost damage to the roots. For protection, you can wrap your pots in jute bags, for example, or put them in a sheltered place.

Problems can also occur in wet winters, because houseleeks do not tolerate wetness at all. Therefore, make sure that water does not collect in the pot and saucer of stone roses in pots and that good drainage of the soil is always ensured for houseleeks in the open.

Propagate houseleek: Offshoots and more

Houseleeks naturally reproduce similarly to strawberries via cuttings and seeds. If you originally have only one rosette of leaves, you can observe it in its vicinity and with time it may spring more and more rosettes. In each case, these are individual, compressed shoots that are viable on their own. If a rosette blooms and then dies, it does not mean the death of the whole plant, but only this one rosette. The other rosettes also form a few offshoots until their own flowering, so that over time you have a carpet of houseleeks.

Propagating houseleek with offshoots

For the amateur gardener it is easier to implement the method of propagation of Sempervivum via cuttings. In the case of propagation via offshoots, the daughter plants are genetic clones of the mother, because they have almost the same genetic material. The best time to do this is in the spring, but it can be done into the fall. The procedure is the same for all species:

1. Prepare the new location for your Sempervivum offshoot. What to look for is described in more detail in our article on planting and caring for Sempervivum. In any case, it should get a lot of sun and be characterised by a lean, permeable substrate.
2. Carefully separate one leaf rosette from the rest by pulling them apart with your fingers. A sterile knife can be used to cut through connecting pieces of shoots and roots.
3. Try to pull out as many roots as possible with the offshoot. This will make it easier for the houseleek offshoot to grow later. Do not be afraid if your offshoot has retained few roots: Houseleeks are able to form a new root system relatively quickly.
4. Plant the cutting in its new location and water it lightly.
   Planting in houseleeks often just means laying them flat in a trough and pressing lightly.
5. As of now, the houseleek requires little to no care.

Propagate houseleek from seed

If propagating houseleeks via cuttings is so easy, why bother with growing new plants from seed? Perhaps the reasons are also with you experimentation and curiosity. Houseleeks newly grown from seed undergo genetic recombination through pollination of the flower. So, seedlings will always look a little different from their parents. This is especially prominent when plants from different origins interbreed.

1. Harvest seeds from faded, already dried seed heads. The seeds are very small and sometimes difficult to see with the eye.
2. Store the seeds in a cool, dark and dry place until sowing.
3. Houseleek seeds require a cold stimulus to break dormancy. In this case, the temperature must be slightly above 0 °C for a period of 2 – 4 weeks. So, you should either store the seeds in the refrigerator for a few weeks before sowing or sow them outdoors already in the fall and leave them there.
4. Fill a shallow tray with dampened growing soil. A good soil to use here is our Plantura Organic Herb & Seedling Compost. It is low in nutrients, permeable and also completely peat-free, which is why its production emits a full 60% less CO₂ than comparable soils.

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5. Spread the individual Sempervivum seeds on the soil at least 3 cm apart and press them lightly. Attention: do not cover them with substrate, because Sempervivum is a light seedling.
6. Now the bowl is placed outside in a bright, somewhat sheltered place. The substrate should not dry out completely, but also in any case should not be consistently wet.
7. About March you can see the first seedlings. While waiting until the plantlets are a little larger, continue to make sure that the substrate is too dry rather than too moist.
8. Houseleeks grow rather slowly. Thus, it may well happen that species in the first-year form only leaf rosettes 1-2 cm in diameter. Nevertheless, the seedlings can be transplanted to their final location in the fall. What you need to pay attention to when planting Houseleeks, we explain in a separate article.

Use of Sempervivum as a medicinal plant

Housleek has been used as a medicinal plant for a long time already. Among other things, they contain flavonoids such as kaempferol, as well as mucilage and tannins. Studies have demonstrated some medicinal effects of houseleeks, especially Sempervivum tectorum. Thus, houseleek can have analgesic, antioxidant, anti-inflammatory effects and support wound healing. Usually Sempervivum is used only externally, for example, as a houseleek ointment together with other ingredients or by cutting open a leaf and applying the sap to affected parts of the body.

Are houseleeks poisonous?

Basically, Sempervivum is considered non-toxic. As with most plants, however, excessive consumption can lead to nausea and vomiting, among other things.

Houseleeks are especially comfortable in rock gardens. In our dedicated article you can find out how to create a rock garden yourself.