How to Grow Yarrow in Australia

Yarrow (Achillea species), also sold as achillea or milfoil, is a hardy perennial in the daisy family (Asteraceae), grown for flat heads of tiny flowers. Common yarrow 'Cerise Queen' (Achillea millefolium) carries cerise pink heads and spreads by underground stems. Fernleaf yarrow 'Cloth of Gold' (Achillea filipendulina) forms a tall clump of golden plates. Both take drought, frost and poor soil in their stride. The mistake most gardeners make is sowing the tiny seed too deep, when it needs light to sprout.

Three mistakes that matter

1. Sowing too deep. Light triggers germination, so a seed covered with even a few millimetres of mix can sit dormant and never show. Scatter it on the surface, press it down and at most dust it with vermiculite.
2. Treating it like a vegetable. Rich soil, heavy feeding and constant water give soft stems that flop in wind and rain, and wet roots rot. Plant in lean, free-draining soil in full sun, and let the surface dry between waterings.
3. Letting 'Cerise Queen' run and seed. Common yarrow spreads by rhizomes (creeping underground stems) and by self-sown seed. It has gone wild in every state except the Northern Territory and is a serious weed of the Australian Alps. Deadhead before seed ripens and plant it away from bushland.

When to plant

Yarrow sprouts when the mix sits between 18 and 24°C. In frosty gardens, raise seedlings under cover in spring and plant them out after the last frost. In frost-free districts, sow in the cooler, drier months, because yarrow grows best away from humid heat. One sowing is enough: each plant lives for years.

If spring runs cold, a seedling heat mat holds the tray at the right warmth. Sowings made late in a window often flower best in their second summer.

Site, soil and setup

Yarrow stays put for years, so it needs no rotation; give it a permanent spot at the edge of a border or a dry bank. Because 'Cerise Queen' spreads sideways, set a buried edging or a path along the side you want kept clear.

Container growing

'Cerise Queen' suits a pot, which also stops it spreading. Give one plant a pot at least 30 cm wide, about 15 L. For 'Cloth of Gold', use a pot at least 40 cm wide, about 30 L, heavy enough not to tip over. Use premium potting mix with about a third coarse sand or perlite mixed through.

• Watering. Water when the top 3 cm of mix is dry, and never leave the pot standing in water. See watering pots through summer.
• Feeding. Give fish and seaweed blend at 25 mL per 9 L once a fortnight from spring until the first flowers, then stop.
• Position. Full sun, sheltered from the strongest wind.
• Renewal. Lift, divide and repot into fresh mix at the intervals given under Deadheading.

Sowing Seeds

Raise yarrow in punnets or cell trays, then plant it out as sturdy young plants.

Starting under cover

• Fill a punnet or cell tray with fresh seed raising mix, firm it and water it first.
• Mix the seed with a pinch of dry sand and scatter it thinly, as in sowing tiny seeds.
• Press it onto the surface. Leave it uncovered, or add a thin dusting of vermiculite to hold moisture.
• Mist, or water from below, and keep the tray bright and at the temperature under When to plant.
• Seedlings appear in 1 to 2 weeks. Grow them on cool, about 13 to 18°C, in full light.
• Move each seedling to its own cell or 8 cm pot once it has true leaves and can be handled.

Sowing direct

Seed can go straight into a raked, weed-free bed in mild weather after the last frost. Press it onto the surface, mist it daily until seedlings show, then thin them to the spacing in the table. Trays are safer, because tiny seedlings are easily lost to drying wind and weeds.

Transplanting

Plant out 8 to 10 weeks after sowing, when roots fill the cell. First harden them off (a week or more of longer outdoor stays, so leaves toughen to sun and wind), as in hardening off seedlings. Set each plant with its crown level with the soil and water it in with seaweed solution at 30 mL per 9 L.

Care by growth stage

Restraint decides how well yarrow grows: keep seedlings just moist, then water less and feed almost nothing once plants establish.

Week ranges run from the sowing date. If growth stalls in very poor sand, a light dose of all-purpose controlled release granular (NPK around 14-5-10), scratched in once in spring, can help.

Deadheading

Removing spent heads brings more flowers, tidies the plant and stops 'Cerise Queen' seeding itself about.

• Cut each faded head back to the side buds on its stem, so they open next.
• After the main flush, cut flowered stems back to the leafy base; a smaller autumn flush may follow.
• For shorter, sturdier 'Cerise Queen', shear the stems back in late spring, before buds form.
• Cut dead stems to ground level in late winter or early spring, before new growth starts.
• Pull up runners of 'Cerise Queen' that stray beyond their space, roots and all. Bin them and unwanted divisions rather than composting or dumping them, because every rhizome piece can regrow.
• Divide 'Cerise Queen' every 2 to 3 years and 'Cloth of Gold' every 3 to 4 years, as in dividing perennials.

Companion planting

Yarrow belongs in a sunny, dry border or on the edge of the vegie patch, where its flower heads feed hoverflies, lacewings and ladybirds.

Grows well with

• Coreopsis and rudbeckia, sun-loving perennial daisies with the same lean, dry needs.
• Lavender, which likes the same gritty, free-draining soil.
• Salvia, whose flowers draw beneficial insects alongside yarrow.
• Sea holly, whose steely blue heads suit the same dry, sunny beds.
• Vegetable beds, where yarrow flowers draw hoverflies whose larvae eat aphids.

Keep apart

• Lettuce and other crops that need rich, constantly moist soil, which yarrow resents.
• Low, slow plants such as violas, which spreading 'Cerise Queen' can smother.
• Citrus trees, whose feeder roots compete; plant yarrow just outside the root zone.

Harvesting Blooms

Cut yarrow once the small flowers across a head have opened and pollen dusts their centres.

• Pick early in the day, while stems are full of water, and carry a bucket to plunge them into.
• Cut just above a side bud or at the base, and the next heads follow as with deadheading.
• Strip the lower leaves from each stem before it goes into the vase.
• For drying, choose firm, fully open heads that have not begun to brown.

Cut stems usually last 7 to 12 days in a vase. To dry them, tie small bunches and hang them upside down somewhere dark, dry and airy until the stems snap cleanly.

Handling yarrow can irritate skin and make it more sensitive to sunlight, so wear gloves and long sleeves. Common yarrow is listed as toxic to dogs, cats and horses, so keep cuttings away from pets that chew. Use fresh heads in mixed posies, and dried 'Cloth of Gold' in wreaths and winter arrangements.

Common problems

Empty trays. Seed sown too deep (see Three mistakes that matter), a surface allowed to dry or a cold tray is nearly always to blame. Read more

Thin, leaning seedlings. Too little light, or warmth without light, makes seedlings lanky; move trays into full light and grow them cooler. Read more

Stems flop open. Besides the causes in Three mistakes that matter, shade and summer storms weaken stems; full sun, shelter and the late spring shear under Deadheading help. Tall 'Cloth of Gold' can still need support, most often in wet weather. In spring, before the stems lean, set a grow-through ring over each clump, or circle it with a few stakes and soft ties.

Plants wilt and rot at the base. Root and stem rots take hold in soil that stays wet, so lift healthy pieces into a raised, free-draining spot. Read more

Yarrow appears in the lawn and paths. Seed from uncut heads and creeping rhizomes are the cause; deadhead as under Deadheading and dig out strays.

Pests and diseases

Yarrow has few serious enemies, and most trouble comes from wet leaves, crowding and seedling rot.

Leafcurl plum aphid (Brachycaudus helichrysi). In Australia this aphid lives on daisy-family plants, crowding onto new shoots and buds and dripping sticky honeydew. Blast small colonies off with the hose; for repeat outbreaks, use soapy water or horticultural oil on a cool day. Read more

Powdery mildew (Golovinomyces species). A grey-white film coats the ferny leaves, worst in warm, humid spells. Remove the worst leaves, thin a crowded clump and spray 1 part full-cream milk to 10 parts water. Read more

Damping off (Pythium species and Rhizoctonia solani). Seedlings pinch in at the base and topple over, rotted by these common soil fungi and water moulds. Read more

Prevention first

• Use new seed raising mix and scrubbed trays for every sowing.
• Keep to the spacings in the variety table, so breezes dry the leaves.
• Bin mildewed or aphid-covered cuttings rather than composting them.
• Look over new shoots weekly in spring, and leave early aphids for hoverflies and ladybirds to find.

Tips

1. Use 'Cerise Queen' as a flowering lawn on a sunny, lightly used patch, mowing high with a rotary mower.
2. Try yarrow in coastal gardens: both species tolerate some salt and wind.
3. Set 'Cloth of Gold' at the back of a border and 'Cerise Queen' in front, so the golden plates rise behind the pink.
4. In cold gardens, mark each clump with a label in autumn, because the tops can die back over winter and vanish.