Anise hyssop

Sun

Full sun to light partial shade; flowering and stem strength are best in full sun.

Water

Water regularly while establishing; once established, water during prolonged dry spells. Avoid persistently wet soil.

Soil

Well-drained sandy, loamy or gravelly soil; average fertility is sufficient. Avoid heavy soil that stays wet in winter.

Height

2-4 ft (0.6-1.2 m)

Spread

1.5-3 ft (0.45-0.9 m)

Flowers

Lavender-purple spikes from midsummer into early autumn.

Foliage

Opposite, toothed, green leaves with pale, softly hairy undersides and a strong anise or liquorice scent when crushed; stems are square.

Growth

Fast; often flowers in its first year from an early sowing.

Care needed

Low

• Water new plants when the upper soil begins to dry; established clumps need less frequent watering.
• Avoid rich feeding, which encourages floppy growth; add a light compost dressing in spring only on poor soil.
• Keep mulch away from the crown, especially where winters are wet.
• Use discreet supports if plants lean in partial shade or exposed positions.
• Remove unwanted seedlings while small, or retain a few to replace ageing plants.

Pruning. Deadhead faded spikes during summer to encourage further flowers and reduce self-seeding. Leave some seedheads for wildlife, then cut old stems close to ground level in early spring before new shoots lengthen.

Early spring

Cut down old stems and remove weeds around emerging shoots.

Spring

Sow seed under cover; a period of cold, moist treatment can improve germination.

Late spring

Plant out hardened-off young plants after severe frosts, allowing room for mature clumps.

Summer

Water during prolonged drought and deadhead selected spikes to extend flowering.

Early autumn

Collect ripe seed, or leave a few spikes to shed seed naturally.

Winter

Leave standing stems where practical and check that water is not collecting around the crowns.

• Repeat small groups through a sunny perennial border to create a rhythm of upright purple spikes.
• Combine with coneflowers, black-eyed Susans and little bluestem for a loose prairie-style planting.
• Plant near a path or seating area where you can brush the aromatic leaves.
• Use in a sunny herb or edible garden for flowers, fragrant foliage and pollinator activity.

Garden styles it suits: Cottage garden, Native meadow, New perennial (prairie), Pollinator garden, Sensory garden and Edible landscape.

Plant it with: Purple coneflower, Black-eyed Susan, Little bluestem, Prairie dropseed, Yarrow and Butterfly weed.

Wildlife: Nectar-rich flowers attract many bees, butterflies and other pollinating insects. Seed-eating birds may visit retained seedheads.

• Crown or root rot in wet soil: improve drainage or move plants to a raised position; do not pile mulch over the crown.
• Powdery mildew: allow more space and airflow, water the soil rather than the leaves, and remove badly affected foliage.
• Slugs and snails on young shoots: inspect plants during damp weather and use barriers or locally approved iron-phosphate bait if needed.
• Floppy stems in shade or rich soil: move to a sunnier position, stop feeding and support stems before they fall.

Not known to be toxic to people, cats, dogs or horses. The leaves and flowers are used as culinary herbs, though veterinary information on this species is limited. This does not establish the safety of concentrated extracts or essential oils.

• Korean mint (Agastache rugosa)

  Very similar, with aromatic foliage and purple spikes. Its leaves generally have greener, less densely white-hairy undersides; hybrids can be difficult to distinguish without a reliable label.

• Hyssop (Hyssopus officinalis)

  A woody-based plant with much narrower leaves and flowers clustered along the upper stems, rather than the broad leaves and dense terminal spikes of anise hyssop.

• Catnip (Nepeta cataria)

  Usually has greyer foliage and loose clusters of small whitish flowers marked with purple, rather than dense lavender-purple spikes; its scent is not strongly anise-like.

The species name foeniculum refers to fennel, reflecting the anise-like scent of the foliage; despite its common name, it is not a true hyssop.

Propagation. Sow seed in spring or autumn, pressing it onto the surface and covering only very lightly. Cold, moist treatment can improve germination. Divide healthy young clumps in spring; plants also self-seed where conditions suit them.

Accepted botanical name

Agastache foeniculum

In the US and Canada

Native in Canada and the lower 48 states.

Native range

Alberta, British Columbia, Colorado, Idaho, Illinois, Iowa, Manitoba, Minnesota, Montana, Nebraska, New Brunswick and North Dakota.

Measured

Average height 94 cm.

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