Black Adder hyssop

Sun

Full sun; light shade is tolerated, but flowering is usually weaker and stems may lean.

Water

Water regularly while establishing. Once established, allow the soil to dry between waterings; water during prolonged drought to sustain flowering.

Soil

Well-drained sandy, gravelly or loamy soil, preferably of low to moderate fertility. Avoid heavy soil that stays wet in winter.

Height

2-3 ft (0.6-0.9 m)

Spread

1.5-2 ft (0.45-0.6 m)

Flowers

Midsummer to early autumn; violet-blue flowers on dense spikes with dark purple buds and calyces.

Foliage

Green, toothed, pointed leaves with an anise-like scent when rubbed; foliage dies back in winter.

Growth

Moderate to fast; often flowers well in its first growing season.

Care needed

Low

• Pollinators
• Deer resistant
• Drought tolerant
• Heat tolerant
• Low allergen
• Fragrant

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Easy

Toughness

Fairly tough

Pick your zone, country, light and whether you have pets.

1. Planting day

   1 ft (0.3 m)

2. After 1 year

   1.6 ft (0.49 m)

3. After 2 years

   2.2 ft (0.68 m)

4. After 3 years

   2.5 ft (0.75 m)

   full size

About 2 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Safe

Growth rate

Fast

• Plant in spring in colder regions so roots establish before winter.
• Water at soil level and let the surface dry between waterings; never leave containers standing in water.
• Avoid heavy feeding, which encourages soft, floppy growth.
• Keep mulch away from the crown; a light gravel mulch suits damp climates.
• Use discreet supports early if stems lean in exposed sites.

Pruning. Remove faded flower spikes during summer to keep the plant tidy and encourage further bloom. Leave the main stems standing over winter, then cut them back just above emerging basal growth in spring.

Spring

Cut back old stems once new growth appears, taking care not to damage basal shoots.

Spring

Plant in a sunny, freely drained position and water thoroughly.

Late spring

Take softwood cuttings from healthy, non-flowering shoots.

Summer

Water newly planted specimens during dry spells and remove spent flower spikes.

Early autumn

Leave some late flower spikes for structure and stop feeding.

Winter

Check that water drains away from the crown and move pots out of persistent rain if necessary.

• Repeat small groups through a sunny perennial border to create a rhythm of upright purple spikes.
• Combine with ornamental grasses and coneflowers for a loose, long-flowering planting.
• Use in a gravel garden alongside lavender and catmint, where drainage suits all three.
• Place near a sunny path or seating area where the scented foliage and visiting pollinators can be enjoyed.

Garden styles it suits: Cottage garden, New perennial (prairie), Pollinator garden, Dry gravel garden, Sensory garden and Blues and silvers.

Plant it with: Purple coneflower, Feather reed grass, Catmint, Lavender, Yarrow and Russian sage.

Wildlife: Flowers attract bees, butterflies and other nectar-feeding insects. Hummingbirds may visit in North America.

• Winter crown or root rot: improve drainage, keep the crown free of wet mulch and avoid planting in winter-wet clay.
• Slugs and snails on emerging shoots: inspect young growth and use barriers, hand-picking or locally approved iron-phosphate bait.
• Powdery mildew: provide good airflow, avoid crowding and water the soil rather than the foliage.
• Floppy stems: provide more sun, reduce feeding and support stems before they fall.

Not known to be toxic to people, cats, dogs or horses. Cultivar-specific safety information is limited, and it is grown as an ornamental rather than a food plant; avoid deliberately feeding any part to pets or livestock.

• Anise hyssop (Agastache foeniculum)

  Very similar aromatic foliage and purple flower spikes; 'Black Adder' generally has darker buds and longer, denser spikes. A reliable nursery label is the best confirmation.

• Korean mint (Agastache rugosa)

  Usually has broader, more triangular leaves and paler purple flower spikes. Hybrids can be difficult to distinguish without a label.

• Common hyssop (Hyssopus officinalis)

  A smaller, woody-based plant with narrow leaves, rather than the broad, toothed leaves of 'Black Adder'.

Agastache comes from Greek words meaning 'many' and 'ear of grain', referring to the numerous flower spikes.

Propagation. Take softwood cuttings in late spring or early summer, or divide healthy established clumps in spring. This hybrid is generally sterile; seed is not a reliable way to reproduce the cultivar.

Accepted botanical name

Agastache

Sources: GBIF (CC BY 4.0). The care and design notes are LandscapeGPT's own.