Agastache 'Blackadder'

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giant hyssop 'Blackadder'

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giant hyssop 'Blackadder' RHS
giant hyssop 'Blackadder' RHS
giant hyssop 'Blackadder' RHS
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Herbaceous Perennial
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A hardy and reliable perennial with long, pointed green, aromatic foliage with toothed edges. Tall, upright spikes of dark violet-purple to dark blue bottlebrush-like flowers appear from July to October

Position

Full sun

Soil Types

Chalk, Loam, Sand

Max Height

0.5-1 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity
2–5 years
Max Spread
0.1-0.5 metres
Max Height
0.5-1 metres

Growing Conditions

Chalk Loam Sand
Moisture
Well–drained
pH
Acid or Alkaline or Neutral

Position

Full sun
Aspect
West–facing or South–facing
Exposure
Sheltered
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 & Scent

Fragrance Flower
Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Lamiaceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Bushy
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
Name Status
Accepted

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

  • Cottage and informal garden
  • Gravel garden
  • Mediterranean climate plants
  • Banks and slopes
  • Flower borders and beds

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