• AGM plants

    AGM plants have been through a rigourous trial and assessment programme. They are:

    • Excellent for ordinary use in appropriate conditions
    • Available to buy
    • Of good constitution
    • Essentially stable in form & colour
    • Reasonably resistant to pests & diseases

Sempervivum arachnoideum

Cobweb houseleek

AGM plants

AGM plants have been through a rigourous trial and assessment programme. They are:

  • Excellent for ordinary use in appropriate conditions
  • Available to buy
  • Of good constitution
  • Essentially stable in form & colour
  • Reasonably resistant to pests & diseases
Cobweb houseleek

© � RHS 2002

  • Other common names Cobweb houseleek
    Cobweb sedum

  • Genus Sempervivum are evergreen perennials forming mats of fleshy-leaved rosettes, often attractively coloured, with star-shaped pink or pale yellow flowers in summer

  • Family Crassulaceae / Crassulaceae

  • Species S. arachnoideum is an evergreen perennial forming a mat of fleshy rosettes 1-3cm across, leaves green or reddish, with cobwebby white hairs at the tips. Starry pink flowers 1cm in width in flat cymes on stems to 12cm

  • Plant range Pyrenees to Carpath.

Characteristics

  • Foliage Evergreen

  • Habit Mat forming

  • Hardiness

    Hardiness ratings

    All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets

    • H1a - Under glass all year (>15C)
    • H1b - Can be grown outside in the summer (10 - 15)
    • H1c - Can be grown outside in the summer (5 - 10)
    • H2 - Tolerant of low temperatures, but not surviving being frozen (1 to 5)
    • H3 - Hardy in coastal and relatively mild parts of the UK (-5 to 1)
    • H4 - Hardy through most of the UK (-10 to -5)
    • H5 - Hardy in most places throughout the UK even in severe winters (-15 to -10)
    • H6 - Hardy in all of UK and northern Europe (-20 to -15)
    • H7 - Hardy in the severest European continental climates (< -20)
    Old hardiness ratings

    While we update our systems with the new hardiness ratings you may still see old hardiness ratings in your search results. These are denoted as 'Old'.

    • H1 - Requires heated glass
    • H2 - Requires unheated glass
    • H3 - Hardy outside in some regions of the UK
    • H4 - Hardy throughout the UK
    • H1 + H3 - Requires heated glass but may be grown outside in summer

    For full details of the hardiness ratings see

    see more

    H5

Colour

Sunlight

  • Full Sun

  • Aspect South-facing or North-facing or West-facing or East-facing

  • Exposure Exposed or Sheltered

Soil

  • Chalk

    Sand

  • Chalk

    Loam

  • MoistureWell-drained

  • SoilSand, Loam

  • pHAcid, Alkaline, Neutral

Size

  • Ultimate height

    Up to 10 cm

  • Ultimate spread

    0.1-0.5 metres

  • Time to ultimate height

    5-10 years

How to grow

Cultivation Grow in moderately fertile well-drained soil in full sun. Protect from excessive winter wet. Suitable for rock garden, scree bed, wall crevice, trough or alpine house

Propagation Propagate by seed sown in spring, or root offsets in spring

Suggested planting locations and garden types Flower borders and beds Garden Edging Ground Cover Cottage & Informal Garden Gravel Garden Rock Garden Patio & Container Plants

How to care

Pruning No pruning required

Pests Can get vine weevil

Diseases May be subject to a rust

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