How to Grow Anise Hyssop in Australia

Anise hyssop (Agastache foeniculum) is a short-lived perennial of the mint family, Lamiaceae. It is grown for aniseed-scented leaves and long purple flower spikes that draw bees all summer. Despite the name it is neither anise nor hyssop, and it comes from the prairies of North America. Once settled it handles dry spells and light frost, and the usual mistake is burying its tiny seed.

Three mistakes that matter

1. Burying the seed. Anise hyssop seed needs light to germinate, so a normal covering of soil leaves most of it asleep. Sow it on the surface, as Starting in trays describes.
2. Planting into heavy, wet soil. Poor drainage is the most common reason plants fail, because crowns and roots rot in soil that stays wet. Grow it in light, free-draining soil, or build a raised bed or mound on clay.
3. Feeding it like a vegetable. Rich soil and too much nitrogen give soft, floppy stems and fewer flowers. Over-feeding also reduces the essential oils that give anise hyssop its flavour and aroma, so a yearly layer of compost is enough.

When to plant

Seed germinates best with the mix at 20 to 22°C, and it will still come up between 10 and 25°C, only more slowly. Plant spring sowings out once frost has passed. Plant autumn sowings out as soon as they are big enough, so they settle before winter, unless the zone note says to wait. One sowing gives plants for several years, so there is no need to sow in succession.

In frosty districts, start trays under cover about 6 weeks before the last frost and plant out around Melbourne Cup weekend. At the hot edge of a window, keep trays in bright shade so the mix stays moist.

Site, soil and setup

Choose a permanent spot, because the clump stays put for several years and dislikes regular digging.

As a perennial it sits outside the vegetable rotation, so give it a bed edge, herb bed or border near the vegie patch. Gardening Responsibly, a weed-risk project supported by the NSW Government, rates it lower risk and finds no evidence that it is invasive.

Container growing

Anise hyssop grows well in a pot of at least 20 L, about 40 cm across. A standard 40 cm pot holds about 28 L. Fill it with a premium potting mix. The anise hyssop we sell grows 50 to 80 cm tall, which suits a large pot on a sunny patio.

• Water: when the mix is dry about 5 cm down, soak it until water runs from the drainage holes.
• Feed: fish and seaweed blend at half strength, about 12.5 mL per 9 L, fortnightly in spring and summer.
• Position: full sun, out of strong wind, which pushes the tall stems open.

Sowing Seeds

Start anise hyssop in trays: the seed is small and the seedlings are slow, and a tray lets you control light, moisture and slugs.

Starting in trays

• Fill a tray or punnet with fine seed-raising mix.
• Scatter the seed thinly, press it onto the surface, and cover with no more than a 1 mm dusting of mix or vermiculite.
• Keep the mix evenly moist but never soggy, in bright light.
• Expect seedlings in about 10 to 20 days at the temperature When to plant gives, and allow 1 to 3 months in cooler mix.
• Prick out seedlings (lift each by a leaf) into their own pots once they can be handled.

Planting out

• Plant out once seedlings have true leaves and stand 5 to 10 cm tall.
• First harden them off (set them outside a little longer each day so they adjust to sun and wind) over about a week.
• Space plants 30 to 40 cm apart, with 30 to 45 cm between rows.
• Water them in with seaweed solution at half strength, 15 mL per 9 L.

Direct sowing works in a fine, weed-free bed that you can keep damp until germination. Mark the row, because the seedlings are hard to tell from weeds. Thin them at two sets of true leaves to the spacing Planting out gives.

Care by growth stage

Drainage and restraint decide this crop: young plants need steady moisture, while established clumps prefer to dry slightly between deep waterings.

Growth slows in winter and returns strongly in spring. Water less in the cooler months and spread a 5 cm layer of compost around the clump each spring, keeping it clear of the crown. If growth stalls in very poor soil, a light scatter of all-purpose controlled release granular (NPK around 14-5-10) can help.

Cutting Back

A few cuts through the year keep the clump bushy and flowering, and decide how much it self-seeds.

• Pinch the growing tips of young plants to encourage bushier growth.
• Deadhead fading spikes just above a set of leaves to bring on more flowers.
• Leave a few spikes to ripen if you want self-sown seedlings to replace old plants.
• Cut the whole plant back in late winter to make way for fresh spring growth.
• Divide crowded clumps in spring or autumn, replanting large pieces straight into their new spot.
• Pull unwanted seedlings while small, when they come out easily.

Companion planting

The flowers pull bees and other beneficial insects into the garden, so plant anise hyssop where fruiting crops and dry-loving herbs can share them.

Grows well with

• Tomatoes and pumpkins, which gain from the pollinators it brings in.
• Thyme and oregano, which also want sun and free-draining soil.

Keep apart

• Mint, whose runners crowd the clump and which wants evenly moist soil.
• Plants that need constantly wet soil, since shared watering would rot anise hyssop.

Harvesting Leaves and Flowers

Pick leaves once a plant can spare a few stems, usually from about 10 weeks after sowing. Pick flowers once the spikes colour up.

• Pick in the cooler part of the day, when the leaves are fresh and aromatic.
• Snip young tips or single leaves with scissors, taking a little from each plant.
• Take only light pickings from young plants, since hard cutting slows their recovery.
• For drying, cut leafy stems just past full bloom, when the oil content of the leaves peaks.
• Cut flower spikes for drying when they are partly open.

To dry, hang small bunches upside down in a warm, shaded, airy spot. Store the dried leaves and flowers in airtight jars away from light and moisture.

Leaves and flowers flavour salads, fruit, desserts and rice, and the leaves make a pleasant aniseed tea. They leave the mouth feeling dry, so use them in small amounts.

Common problems

Leggy seedlings. Seedlings stretch when a tray sits in poor light or grows too crowded, so move it to brighter light and prick out on time. Read more

Seedlings collapse at soil level. Damping off (a fungal rot of seedling stems) follows soggy mix and still air. Use clean seed-raising mix, water gently and give the tray more air. Read more

Plant rots at the base. Crown and root rot follows soil that stays wet. Water less, and replant on a mound or in a pot, as Three mistakes describes.

Few flowers and floppy plants. Shade and exposed, windy sites both give weak, open plants with fewer spikes, so move them into full sun; Three mistakes covers feeding.

Old plants thin out. Anise hyssop is short-lived, and clumps often decline after a few years. Keep a few self-sown seedlings, or divide the clump as Cutting Back describes.

Pests and diseases

Few pests trouble anise hyssop, and most damage falls on seedlings or on plants stressed by humid, crowded conditions.

Slugs and snails, including grey field slug (Deroceras reticulatum). They chew soft young growth and seedlings, feeding at night and after rain. Pick them off by torchlight, set beer traps, or use an iron-based bait as the label directs. Read more

Aphids (family Aphididae). Small sap-sucking insects cluster on the soft tips, though they are rarely serious on this crop. Hose them off with a firm jet of water or squash them by hand, and leave ladybirds and lacewings to finish the job. Read more

Powdery mildew (fungi of the order Erysiphales). White powdery patches spread over the leaves in humid, still weather and on crowded plants. Remove the worst leaves, and spray early outbreaks with 1 part full-cream milk to 10 parts water. Read more

Prevention first

• Raise seedlings in trays and plant them out at the size Planting out gives, when they are less vulnerable to slugs.
• Keep the full spacing Planting out gives, so air moves between plants.
• Water at the base, never over the leaves.
• Check the soft tips each week while plants are in active growth.

Tips

1. Cut a few flower spikes for a vase, or hang them to dry for arrangements.
2. Save seed by letting spikes dry on the plant, then cut them into a paper bag and rub out the seed. Store it cool, dry and dark.
3. Move self-sown seedlings while they are small. They wilt at first but usually recover within a few days.