Anise hyssop (Agastache foeniculum) is a clump-forming perennial herb in the mint family, native to the prairies and open woodlands of north-central North America. Despite the common name, it isn't closely related to true hyssop; it picked up the name mostly from its upright, spike-flowered habit, while "anise" refers to the sweet licorice scent its leaves give off when brushed or crushed. In Kentucky gardens it's a fully hardy perennial, dying back to the ground over winter and returning from the same crown each spring. Anise hyssop is about as easy as herbs get, asking for little beyond full sun and soil that drains well, and it tolerates drought once established. The reward for that modest effort is months of lavender-blue flower spikes that pull in bees, butterflies, and hummingbirds from early summer into fall.
Sowing and planting
Start seed indoors 6 to 8 weeks before the last expected frost, which in zone 6b puts sowing around mid-March. Anise hyssop seed needs light to germinate, so press it onto the surface of a moist seed-starting mix rather than burying it, and keep the tray around 65 to 70°F (18 to 21°C); germination takes 10 to 20 days and can be uneven. Seed can also be sown directly outdoors once the soil has warmed in late spring, scattered thinly and barely covered, though indoor starts generally establish more reliably in a Kentucky spring. Transplant or thin seedlings to 18 inches (45 cm) apart once they carry a couple sets of true leaves, choosing a full-sun spot with soil that drains freely; anise hyssop sitting in heavy, waterlogged clay over winter is prone to rot. Nursery-grown plants or divisions from an established clump can go into the garden anytime from mid-spring through early fall, watered in well at planting.
Growing on
Water new plants regularly through their first season while roots establish, then ease back once growth is strong; settled-in anise hyssop handles dry spells well and actually prefers soil on the lean, well-drained side over rich, moisture-retentive beds. Little to no fertilizer is needed, and a yearly topdressing of compost is usually plenty, since heavy feeding tends to produce lanky growth with fewer flower spikes. Pinching the growing tips back once or twice in late spring encourages a bushier plant with more branching stems, though it isn't required for a healthy plant. Deadheading spent flower spikes extends the bloom period and curbs the generous self-seeding this plant is known for, which can turn a single clump into a spreading patch within a couple of seasons if left unchecked. Established clumps benefit from division every three to four years in spring, both to keep the plant vigorous and to produce new plants for other parts of the garden.
Harvesting
Leaves and tender stems can be picked as soon as the plant is established and growing well, generally from about 8 weeks after sowing or shortly after a transplant settles in. Because this is a leafy perennial rather than a crop with a single harvest window, it keeps producing fresh growth to pick through the whole season, right up until a few weeks before the first hard frost. Harvest in the morning once the dew has dried, when the leaves' aromatic oils are most concentrated, snipping stems just above a pair of leaves to encourage the plant to branch. The flower spikes open over many weeks starting in early to mid-summer and can be picked individually for fresh use in salads or as a garnish, or cut whole and hung to dry in a warm, airy spot out of direct sun; both leaves and flowers are edible and carry the same sweet, licorice-like flavor. Dry leaves the same way as the flowers, then once brittle strip them from the stems and store airtight and out of light, where the scent holds for the better part of a year. Stop picking a few weeks before the first expected frost so the plant can store enough energy in its roots to overwinter well.
Problems and pests
Grayish-white powdery coating on the leaves
Powdery mildew shows up on anise hyssop most often in late summer, when humid days follow cool nights and plants are crowded together with poor airflow. It rarely kills an established clump but can look unsightly and weaken late-season growth. Space new plantings a full 18 inches (45 cm) apart, divide crowded clumps, and water at soil level rather than overhead to keep foliage dry.
Leaves chewed ragged or skeletonized
Japanese beetles are drawn to anise hyssop's foliage in mid- to late summer, stripping leaves down to their veins in bad years. Handpicking beetles into a bucket of soapy water each morning keeps small infestations in check, and a lightweight floating row cover (a fine fabric laid over the plants) protects young, newly planted clumps until they're established enough to shrug off damage.
Center of the clump flopping open or going bare
A mature clump that sprawls outward with a thin, woody middle has usually gone too long without division or is growing in too much shade or overly rich soil. Divide the clump every three to four years in spring, move plants into full sun if they're stretching toward light, and hold off on rich feeding, which encourages the kind of soft growth that flops.
Seedlings coming up everywhere
Anise hyssop self-seeds freely, and a single mature plant left to flower and set seed can fill a bed with volunteers within a season or two. Deadhead spent flower spikes before seed drops if you want to limit spread, and hoe out unwanted seedlings while they're small and easy to pull.
Roots rotting over winter or in a wet spring
Soggy, poorly drained soil, especially through a cold, wet winter, causes crown and root rot in anise hyssop, which otherwise tolerates far more neglect than overwatering. Plant in raised beds or mounded rows where drainage is questionable, and avoid siting new plants in low spots where water collects after rain.
Varieties worth growing
- Golden Jubilee – Chartreuse-gold foliage that contrasts well with the blue flower spikes, grown as much for its colorful leaves as for its blooms.
- Black Adder – A vigorous selection with unusually long, deep violet-blue flower spikes and a long bloom season, popular with pollinators and cut-flower growers alike.
- Blue Fortune – A sterile hybrid agastache that doesn't set seed, useful where self-sowing anise hyssop would otherwise be a problem, with sturdy upright blue flower spikes.
- Honeybee Blue – A compact selection that stays under 2 feet (60 cm) tall, well suited to smaller beds, containers, or the front of a border.
- Korean mint (Agastache rugosa) – A closely related species with a similar anise scent and growing habit, traditionally used in Korean and Chinese herbal teas.