How to grow sempervivum

What are sempervivums?

Sempervivums are mostly hardy, evergreen succulents

A group of plants that have thick, fleshy leaves or stems that are able to store water. This allows them to survive in arid habitats with low moisture.

, originating from mountainous regions of Europe and Asia. Their common name, houseleek, refers to their traditional useage of growing on

Transferring young plants from one container to a slightly larger one, where they will have more room to grow and fresh potting compost. This encourages continuous, healthy growth.

house roofs.

Choosing sempervivums

Most houseleeks are easy to grow and form dense ground-hugging mats. There are quite a few to choose from though so let's take a look at what to consider before you make your purchase;

• Your main deciding factor is most likely foliage colour and how they contrast with other houseleeks or alpine companions. Colour is quite fluid in houseleeks. Foliage can change colour - often from green to red - depending on the time of year and temperature. Some have contrasting leaf tip colour to the rest of the plant. Others have a more dominant leaf colour whether green, red or grey, or blue-green.

Choosing sempervivum by colour

• Leaf texture is another element of choice. A few houseleeks have a 'cobweb' of white hairs over them such as Sempervivum ciliosum.
• Check out our favourites on our sempervivum by foliage page or go to RHS Find a Plant and search by your preferred foliage colour.
• Although foliage is the most important feature of a houseleek, mature rosettes
  

  Rosettes are the circular arrangement of flower petals; or a cluster of leaves radiating from approximately the same point usually around a stem. Examples include aeonium and most succulent plants, African violets, primula, sempervivums.

  will flower in summer. Flower clusters may be green such as Sempervivum calcareum 'Guillaumes', pink, as with S. 'Hayling' or purple, e.g. S. tectorum.
• Most sempervivum are fully hardy. However a few (check label before buying), especially the grey or hairy ones, dislike winter wet so may need bringing under cover or protecting from the worst of the wet.

If you select plants with an AGM award (Award of Garden Merit) they have been trialled by the RHS for attractiveness and reliability, so they're recommended to perform well in your garden.

Flowers

Houseleeks flower in summer after 2-3 growing seasons. While flowers add interest, the foliage is the main attraction. A flower stalk is sent up from the middle of the rosette to a height of around 15-20cm (7-9in). After flowering this central rosette dies, but there should be plenty of mini plants by then to replace it. These are produced by the rosette sending out a spray of horizontal stems (stolons) with mini rosettes attached to the ends. These then root. 'Hen and chickens' is one of sempervivum's common names, referring to this growth pattern.

Buying sempervivums

Although houseleeks can be bought at any time of year. They are usually sold in small pots (about 9cm) in garden centres, from specialist alpine nurseries and by mail order.

Fernwood Nursery holds the National Collection of species and cultivars and is a good place to go for more unusual varieties.

Buying: garden centre plants

Buying: mail order plants

When to plant sempervivums

While they can be planted at any time of year, spring is ideal to get them nicely established during the warmer growing months.

Where to plant sempervivums

You'll need a well-drained site such as a rock, scree or gravel garden. Alternatively, grow sempervivums in containers whether shallow alpine pans, old bricks, troughs, gutters or sinks. They can also plug holes in dry stone walls! Or pop them into living walls and green roofs.

They are not fussy as to soil type in terms of pH

This describes how acid or alkaline soil is, and is expressed as a number between 0 and 14. Soil with a pH of 7 is neutral, an acid soil has a lower value, and an alkaline soil has a higher one. Most plants grow best in soil that’s within a specific pH range, so it’s useful to know your soil’s pH. Testing kits are easy to use and widely available in garden centres and online.

but avoid heavy soils like clay that drain poorly.

Also when positioning houseleeks, have a think about their eventual size. Plants rarely get more than 15cm (6in) tall but will spread to at least 30cm (1ft) by stolons and rooting rosettes

Rosettes are the circular arrangement of flower petals; or a cluster of leaves radiating from approximately the same point usually around a stem. Examples include aeonium and most succulent plants, African violets, primula, sempervivums.

. In good conditions, vigorous plants may outgrow their space and need splitting up in spring. Others will need repotting or infilling with young offsets every few years if flowered patches have died out.

Alpines for dry stone walls

Green roofs

Gravel gardens

Scree gardening

How to plant sempervivums

Plant out at the same level as the rosettes are in their pots, firming in gently. Dress the surface of your soil or pot with grit, slate or some small aggregate. This helps keep soil off the leaves, but also acts as a foil, showing the rosettes off to perfection.

If you are planting in containers, prepare a free-draining growing medium. Here's how;

• 1 parts soil-less compost
  

  Can refer to either home-made garden compost or seed/potting compost:

  
  • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own.

  (for example a peat-free potting compost), one part loam-based compost such as John Innes No.1 or No.2 and one part sharp sand

  Sharp sand is washed, gritty sand used in potting compost mixes, This is sold for gardening and is not the same as builders sharp sand.

  .
• A basic alpine trough mix of half sharp grit and half John Innes No. 2 will also offer enough drainage. You can add a slow release feed. Check the product label for the application rate.
• If you aren't able to mix your own, buy a ready made alpine or cacti potting compost.

Watering

While sempervivum appreciate being watered in dry in spring or summer weather, they can survive happily without.

Plants out of doors will not need watering in winter.

Feeding

While any slow release feed you've included in the potting medium will last several months, once that has been used up, you can supplement with a monthly general liquid feed in the growing season

The period of time when an individual plant is in active growth. This will depend on the local climate and light levels, and can vary between different plants, although it is broadly from spring to autumn.

. Plants growing in the ground are unlikely to need fertiliser.

Overwintering

Houseleeks are generally very hardy, needing little attention in winter. Some will prefer sheltered conditions out of excessive winter wet (check the label when buying) so move containers into a cold frame

Cold frames are glaze box-like structures made from brick or wood with a  hinged or removable, glazed, sloping lid. Useful to protect plants from cold weather over winter or acclimatise (harden off) young plants in spring and provide extra warmth for tender crops in summer.

or place a sheet of perspex over a plant if you live in a wet region.

Ongoing care

To keep your container collection of sempervivum in tip-top conditions, separate and repot plants every 2-3 years in spring. This will let you clear out any dead material and fill gaps left by flowered plants (although you can just gently prize up an offset and pop it with a little more compost

Can refer to either home-made garden compost or seed/potting compost:

• Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own.

into the gap and it will root away).

Displays in the open ground can also be split and replanted in spring when they start to look tired or gappy.

If you don't want plants to self-seed, trim off flowered stalks after they've flowered and before they set seed.

Ensure that over time, or at the height of the growing season

The period of time when an individual plant is in active growth. This will depend on the local climate and light levels, and can vary between different plants, although it is broadly from spring to autumn.

, other plants don't overshade your sempervivums. Cut them back if you need.

Offsets

Propagating by offsets is a sure fire way to get plants the same as your favourite cultivars.

• Pot up offsets (mini rosettes
  

  Rosettes are the circular arrangement of flower petals; or a cluster of leaves radiating from approximately the same point usually around a stem. Examples include aeonium and most succulent plants, African violets, primula, sempervivums.

  ) in spring into a free-draining, gritty compost
  

  Can refer to either home-made garden compost or seed/potting compost:

  
  • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own.

  . You can make your own using half and half sharp grit and John Innes No.2 or buy a ready-made cacti compost. Plantlets may already have roots, so tease rosettes apart carefully. Keep moist and out of direct sun and they should establish in 4-6 weeks.
• If the mini rosettes don't yet have roots, snip off the connecting stolon close to the rosette to encourage rooting. Press the rosette lightly into the surface of a pot of gritty compost. Place somewhere out of direct sun and keep moist until rooted and showing active growth – a process which will take a few weeks.

Seed

If you have a species sempervivium which will come true from seed if not cross pollinated

When a flower has received pollen, so is able to make seeds.

or if you want to experiment, you can grow plants from seed. Named varieties are unlikely to produce offspring that are true to type (i.e. like the parent).

• If you are experimenting with hybridising, pollinate the summer borne flowers by hand using a paintbrush using pollen from cultivars you'd like to try as parents.
• When seed pods brown, crush to extract the tiny seed.
• Sow in potting compost between spring and autumn.
• Place in a sheltered and frost-free spot, such as a cold frame
  

  Cold frames are glaze box-like structures made from brick or wood with a  hinged or removable, glazed, sloping lid. Useful to protect plants from cold weather over winter or acclimatise (harden off) young plants in spring and provide extra warmth for tender crops in summer.

  , to germinate.
• Pot on into a free-draining gritty compost when little plants are large enought to handle.

Sempervivum are generally trouble-free little plants.

One problem which may arise is birds trying to uproot newly planted speciemens. If so, temporarily string arcoss some taut thread to keep them off. Like other containerised plants, they can suffer from soil-dwelling pests like vine weevil. And they can get sempervivum leaf miner, a relatively new pest to the UK.

If plants look peaky, give them a gentle tug to check the root system is strong and if not, tip them out of the container to see if there is an underlying root problem. Excessive moisture will cause roots to rot, so ensure drainage is sharp by having a well-draining compost

Can refer to either home-made garden compost or seed/potting compost:

• Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own.

or soil. Rust is occasionally a problem.

If you're a member of the RHS, you can use our online Gardening Advice Service, via MyRHS, for any gardening queries and problems.