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Herbaceous Perennial

Agastache 'Blackadder'
  • RHS Plants for pollinators

giant hyssop 'Blackadder'

'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

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Size
Ultimate height
0.5–1 metres
Time to ultimate height
2–5 years
Ultimate spread
0.1–0.5 metres
Growing conditions
Chalk
Loam
Sand
Moisture
Well–drained
pH
Acid, Alkaline, Neutral
Colour & scent
StemFlowerFoliageFruit
Spring Green
Summer Black Blue Green
Autumn Black Blue Green
Winter
Position
  • Full sun
Aspect

West–facing or South–facing

Exposure
Sheltered
Hardiness
H4
Botanical details
Family
Lamiaceae
Native to the UK
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

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