Cobweb houseleek

Cobweb houseleek: how do you recognise it?

Habit

Low, dense cushion of rosettes; 5–10 cm tall including the flower stems and up to 30 cm wide.

Leaves

Fleshy, pointed little leaves in rosettes 1–3 cm across, green to reddish, with white hairs between the tips.

Flower

Bright pinkish-red stars on fleshy stems, from June to August.

Growth

Each rosette dies after flowering, but first makes small offsets on short runners.

Roots

Small and shallow; they cannot stand wet feet.

Flowering: June–August · Plants: March–September

Why grow it?

• Attractive all year: the grey-green rosettes with their white ‘cobweb’ stay put even in winter.
• Flowers from June to August with pink starry flowers that attract bees.
• Very drought tolerant: perfect for a trough, bowl, wall or green roof where little else will grow.
• Forms a dense carpet of large and small rosettes all by itself.
• Hardly any work: no pruning, no feeding and almost no watering.

Cobweb houseleek: where does it grow best?

• Full sun: the more light, the more compact the rosettes and the whiter the cobweb.
• Poor, very free-draining soil: sand or loam with plenty of grit, acid to neutral.
• Dry: in wet soil or a saucer of water, the rosettes rot away.
• Sheltered from wet winters, for example under the eaves, on a wall or in a bowl that is slightly tilted.
• Plant 10–15 cm apart; the rosettes soon grow together.

Light

Sun

Soil type

Sand or loam

Acidity

Acid or neutral

Moisture

Dry

Size

0.1 m tall, 0.3 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Stonecrop: Another succulent that needs just as little water and flowers later in summer.
• Creeping thyme: Fragrant cushions between the rosettes, also good for bees.
• Saxifrage: Small alpines that fill a trough nicely together with houseleeks.
• Cheddar pink: Grey foliage and scented pink flowers in the same dry, sunny spot.
• Thrift: Round cushions with pink pompoms; it also likes sun and poor soil.

Cobweb houseleek: when and how to plant it?

Plant in March–September.

1. Plant between March and September, preferably in spring, so the roots are well anchored before winter.
2. Mix potting compost or garden soil half and half with grit or coarse sand; a pot or bowl must have a drainage hole.
3. Set the rosette so that its heart stays just above the soil and firm it in gently.
4. Leave 10–15 cm between plants.
5. Give a very little water to settle the soil, then let it dry out again.
6. Spread a thin layer of fine grit around the rosettes to keep them dry and clean.

Care

Watering

In the garden almost never needed. In a pot only during long droughts, and only once the compost is completely dry.

Feeding

Not needed; fertiliser makes the rosettes soft and less colourful.

Spent rosettes

The rosette that flowered dies: twist or cut it out with its flower stem and fill the gap with a little grit.

Fallen leaves

Remove fallen leaves in autumn; under a wet layer of leaves the rosettes rot.

Repotting

Every 3–4 years, when the bowl is overcrowded: split the rosettes and replant them in a fresh, gritty mix.

Tip: Never leave the rosettes standing in a saucer of water: put the pot on pot feet or on gravel so the water can always drain away. A thin layer of grit keeps the heart of the rosettes dry.

Cobweb houseleek: when to prune it?

When: Cobweb houseleek needs no pruning. After flowering, simply tidy away the spent rosettes.

How:

• After flowering, cut off the dried flower stems together with the dead rosette.
• In spring, remove any dead or rotten rosettes.
• If the bowl gets too full, take out a few rosettes and plant them elsewhere.

Pruning calendar and basic rules

Propagation

Offsets

From April to September: detach a young offset and lay it on dry, gritty compost. It roots within a few weeks, even if it has no roots yet.

Seed

Possible in spring, but seedlings often look unlike the parent, because houseleeks cross easily.

Cobweb houseleek: how does it get through the winter?

Hardy to −30 °C.

• Very hardy, to about −30 °C: frost is never the problem, wet soil is.
• In winter, move pots and bowls under cover or against a wall, out of the rain.
• Remove fallen leaves from the rosettes so no wet layer stays on top of them.
• No covering needed: leaves or fleece only hold moisture in.

Diseases and pests

• Rot: Rosettes turn soft, brown or black, mainly in winter. Cause: soil that is too wet. Remove rotten rosettes and replant the rest in a grittier mix.
• Vine weevil: The grubs eat the roots, after which the rosettes come loose. Mainly in pots. Repot, pick out the white grubs and, if needed, use nematodes against them.
• Birds: Blackbirds pull rosettes out while hunting for insects. Press them back in; a layer of grit helps.
• Soft, stretched rosettes: Too little light or too much fertiliser. Move the plant into full sun and stop feeding.

Through the year

• March: Remove dead or rotten rosettes. Top up the grit.
• April: Planting. Detach and replant offsets.
• May: Planting. Move pots into full sun.
• June: The first flower stems appear.
• July: Flowering. Water pots only in long dry spells.
• August: Remove spent rosettes with their stems.
• September: Last planting and replanting of offsets.
• October: Clear fallen leaves off the rosettes.
• November: Move pots and bowls out of the rain.
• December: Rest. Keep the rosettes dry.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• Each rosette flowers only once and then dies. By then it has made a ring of small offsets that take its place.
• The name Sempervivum means ‘always alive’: the plant stays green all year and survives both frost and drought.
• Charlemagne decreed in one of his ordinances that the gardener should have houseleeks growing on his house. People believed they protected against lightning.