Agastache Black Adder

Description

Agastache ‘Black Adder’ – giant hyssop

Botanical name: Agastache ‘Black Adder’
Common names: Giant hyssop, anise hyssop
Family: Lamiaceae (mint family)
Plant type: Herbaceous perennial
Habit: Upright, bushy, clump-forming
Pot size: 2–3 litre pot
Eventual size: Approx. 60–90cm tall × 45cm spread
Foliage: Aromatic, anise-scented green leaves; deciduous
Flowers: Long, dense spikes of smoky violet-blue flowers from midsummer well into autumn (July–October)
Scent: Aromatic, anise-scented foliage
Aspect / light: Full sun
Soil: Well-drained, fertile; sharp drainage in winter; dislikes wet; any pH
Hardiness: RHS H4 (hardy, to about −10°C); can be short-lived in cold, wet gardens; USDA zones 6–9
Exposure: Warm, sheltered, sunny
Native range: Garden hybrid; the genus is native to North America and Asia
Toxicity / pet & child safety: Generally considered non-toxic to people and pets

Agastache ‘Black Adder’ is a superb perennial bearing long spikes of smoky violet-blue flowers from midsummer into autumn over anise-scented foliage. One of the very best and longest-flowering plants for bees.

GardenAdvice notes

An outstanding pollinator plant, ‘Black Adder’ produces a long succession of dense, smoky violet-blue flower spikes from midsummer right into autumn, held above aromatic, anise-scented foliage. Its exceptionally long flowering season and nectar-rich blooms make it one of the very best perennials for bees and butterflies, buzzing with life for months. It loves a warm, sunny, well-drained spot.

Growing & planting

Plant in spring in well-drained, fertile soil in full sun, in a warm, sheltered spot — sharp drainage, especially over winter, is essential, as cold, wet conditions are its main enemy and can be fatal. Improve heavy soil with grit. Space about 45cm apart. Water while establishing.

Care & maintenance

Low-maintenance in the right spot. Leave the old growth and seed heads standing over winter, both for structure and to protect the crown, then cut back in spring — avoid cutting it down in autumn. Water in dry spells while in growth. It can be short-lived, so it is worth taking cuttings or allowing some self-seeding.

Propagation

• Cuttings: Take softwood cuttings in early summer.
• Division: Divide in spring.
• Seed: May self-seed gently in a warm spot.

Pests & diseases

Generally trouble-free in a warm, well-drained spot. Its main enemy is cold, wet winter soil, which can kill it. Otherwise little troubled by pests, and generally left alone by slugs.

Uses in the garden

Superb in sunny, gravel, prairie-style and cottage borders, wildlife and pollinator plantings, and containers, where its long season of smoky blue spikes brings colour and a constant buzz of bees and butterflies.

Wildlife value

One of the very best plants of all for pollinators: the long-flowering, nectar-rich spikes are hugely attractive to bees, butterflies and hoverflies from midsummer into autumn.

Toxicity & safety

Giant hyssop is generally regarded as non-toxic to people and pets.

GardenAdvice tip

If you want to help pollinators, ‘Black Adder’ is one of the best plants you can grow — it flowers for months and is never without bees and butterflies. The key to keeping it going is drainage: it dies not from cold but from cold, wet winter soil, so give it a sunny, sharply drained spot, leave the old stems on over winter for protection, and cut back in spring. Take a few cuttings as insurance, as it can be short-lived.

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