• AGM plants

    AGM plants have been through a rigorous 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

Agastache 'Blackadder'

giant hyssop 'Blackadder'

  • Other common names giant hyssop 'Blackadder'

  • Family Lamiaceae

  • Genus Agastache are herbaceous perennials with simple, aromatic leaves and small 2-lipped tubular flowers in whorls forming dense spikes, in summer and autumn; some are rather tender but can be grown as annual bedding

  • Details 'Blackadder' is one of the hardiest and most reliably perennial of the genus. Its blue-black spikes of paler-lipped flowers darken in late September and provide winter interest. The aromatic leaves suggest anise

Characteristics

  • Foliage Deciduous

  • Habit Bushy

  • Fragrance Leaf

  • 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)

    H4

Colour

Sunlight

  • Full Sun

  • Aspect South-facing or West-facing

  • Exposure Sheltered

Soil

  • Sand

    Sand

  • Chalk

    Chalk

  • Loam

    Loam

  • MoistureWell-drained

  • SoilSand, Chalk, Loam

  • pHAcid, Alkaline, Neutral

Size

  • Ultimate height 0.5-1 metres

  • Ultimate spread 0.1-0.5 metres

  • Time to ultimate height 2-5 years

How to grow

Cultivation Grow in well-drained fertile soil in full sun. Excellent drainage is especially important during the winter months. It can suffer during cold wet winters

Propagation Root semi-ripe cuttings in late summer and overwinter under cover; propagate by division in spring. This cultivar is sterile

Suggested planting locations and garden types Flower borders and beds Banks and Slopes Cottage & Informal Garden Gravel Garden Mediterranean Climate Plants

How to care

Pruning Trim back stems in late autumn to reduce windrock. Prune flowered stems back in spring

Pests Generally pest free

Diseases Can suffer from powdery mildews

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