Achillea millefolium

The dark blue essential oil of yarrow contains chemicals called proazulenes.[7]

Chamazulene and δ-Cadinol are chemical compounds found in A. millefolium. The chromophore of azulene was discovered in yarrow and wormwood and named in 1863 by Septimus Piesse.

Yarrow contains isovaleric acid, salicylic acid, asparagine, sterols, and flavonoids.[8]

The genus name Achillea is derived from mythical Greek character Achilles, who reportedly carried it with his army to treat battle wounds.[16] The specific epithet millefolium as well as the common names milfoil and thousand leaf come from the featherlike leaves which are minutely divided.[16]

The English name yarrow comes from its Saxon (Old English) name gearwe, which is related to both the Dutch word gerw (alternately yerw)[17] and the Old High German word garawa.[18] In the eastern counties it may be called yarroway.[17] In France, it was called 'herbe de St. Joseph' after a Christian revision of the Achilles story, in which Jesus uses the plant to heal his adoptive father. It has also been called 'carpenter's weed' in this regard.[19][17]

Other names include arrowroot, nose bleed,[17] death flower, eerie, hundred leaved grass, knyghten, old man's mustard, sanguinary,[17] seven-year's love, snake's grass, soldier, and gordaldo.

In New Mexico and southern Colorado, it is called plumajillo (Spanish for 'little feather') from its leaf shape and texture.

Several cavity-nesting birds, including the common starling, use yarrow to line their nests. Experiments conducted on the tree swallow, which does not use yarrow, suggest that adding yarrow to nests inhibits the growth of parasites.[25]

Achillea millefolium is a food source for many species of insects.

Moths

The larvae of the moths Bucculatrix clavenae, B. cristatella, B. fatigatella, B. humiliella, B. latviaella, Cnephasia abrasana, Cochylimorpha elongana, Coleophora argentula, C. carelica, C. ditella, C. expressella, C. follicularis, C. gardesanella, C. millefolii, C. partitella, C. ptarmicia, C. quadristraminella, C. succursella, C. vibicigerella, Depressaria olerella, D. silesiaca, Dichrorampha alpinana (broad-blotch drill), D. petiverella, D. vancouverana (tanacetum root moth), Eupithecia millefoliata (yarrow pug), E. nanata (narrow-winged pug), Gillmeria pallidactyla, Idaea pallidata, Isidiella nickerlii, Loxostege manualis, Phycitodes maritima, P. saxicola, Pyncostola bohemiella, Sophronia sicariellus and Thetidia smaragdaria (Essex emerald) feed on Achillea millefolium in Europe.
The larvae of Chlorochlamys chloroleucaria (blackberry looper), Coleophora quadruplex and Sparganothoides lentiginosana (lentiginos moth) feed on A. millefolium in North America.
Other species of moths with a more cosmopolitan distribution include Aethes smeathmanniana (Smeathmann's aethes moth), Chloroclystis v-ata (v-pug), Choristoneura diversana, Cochylidia richteriana, Epiblema graphana, Eupithecia succenturiata (bordered pug), E. vulgata (common pug), Jordanita budensis and Thiodia citrana (lemon bell). The Noctuid Agrotis stigmosa has also been reared on A. millefolium.[26]

Beetles

Cassida denticollis, Galeruca tanaceti, Hypocassida subferruginea and Phytoecia virgula are cosmopolitan species of beetles that feed on A. millefolium.
Chrysanthia viridissima is a European species whose adults can be found feeding on pollen and nectar.
Trichodes ornatus (ornate checkered beetle) is a species found in North America whose adults can be found feeding on A. millefolium.

True bugs

Horistus orientalis is a species of plant bugs that feeds on A. millefolium.

Wasps

Hedychrum rutilans is a species of cuckoo wasps whose adults can be found feeding on A. millefolium in Europe and North Africa.

For propagation, seeds require light for germination, so optimal germination occurs when planted no deeper than 6 mm (1⁄4 in). Seeds also require a germination temperature of 18–24 °C (64–75 °F). It has a relatively short life in some situations, but may be prolonged by division in the spring every other year, and planting 30 to 46 cm (12–18 in) apart. It can become invasive.[30]

The species use in traditional gardens has generally been superseded by cultivars with specific 'improved' qualities.[31] Some are used as drought-tolerant lawn replacements, with periodic mowing.[32] The many different ornamental cultivars include: 'Paprika',[33] 'Cerise Queen', 'Red Beauty',[34] 'Red Velvet',[35] 'Saucy Seduction', 'Strawberry Seduction' (red), 'Island Pink' (pink),[36] 'Calistoga' (white),[37] and 'Sonoma Coast' (white).[38] The following are recipients of the Royal Horticultural Society's Award of Garden Merit:

• 'Credo'[39]
• 'Lachsschönheit' (Galaxy Series)[40]
• 'Martina'[41]
• 'Lansdorferglut'[42]

The many hybrids of this species designated Achillea × taygetea are useful garden subjects,[43] including: 'Appleblossom', 'Fanal', 'Hoffnung', and 'Moonshine'.[44]

A. millefolium was used in traditional medicine, in part due to its astringent properties and the mild laxative effect of its leaves.[17][50] Yarrow and its North American varieties were traditionally used by many Native American nations.[51] The Navajo historically considered it a "life medicine" and chewed the plant for toothaches and used its infusions for earaches. The Miwok in California used the plant as an analgesic and head cold remedy.[51] Native American nations used the plant for healing cuts and abrasions, relief from earaches and throat infections, as well as for an eyewash.[52] Common yarrow was used by Plains indigenous peoples to reduce pain or fever and aid sleep.[51]

In the early 20th century, some Ojibwe people used a decoction of yarrow leaves on hot stones and inhaled it to treat headaches,[53] or applied decoctions of the root onto skin for its stimulating effect.[54]

The entire plant is reportedly edible and nutritious,[46] but it is advised not to consume much.[55] The foliage is pungent; both its leaves and flowers are bitter and astringent.[17] The leaves can be eaten young; raw, they can be added to salad.[55] The leaves, with an aniseed-grass flavour, can be brewed as tea.[56]

In the Middle Ages, yarrow was part of a herbal mixture known as gruit used in the flavoring of beer prior to the use of hops.[57] The flowers and leaves are used in making some liquors and bitters.[2]

Yarrow is considered an especially useful companion plant, attracting beneficial insects and repelling some pests. It attracts predatory wasps, which drink the nectar and then use insect pests as food for their larvae. Similarly, it attracts ladybirds and hoverflies.[29]

A. millefolium can be planted to combat soil erosion due to the plant's resistance to drought. Before the arrival of monocultures of ryegrass, both grass and pasture contained A. millefolium at a density of about 0.3 kg/ha. One factor for its use in grass mixtures was its deep roots, with leaves rich in minerals, minimizing mineral deficiencies in ruminant feed. It was introduced into New Zealand as a drought-tolerant pasture.[24]

Some pick-up sticks are made of yarrow.

Yarrow can be used for dying wool as it contains apigenin and luteolin. Depending on the mordant the color may be green to yellow.[58]

In the Classical Greek epic Iliad, Homer tells of the centaur Chiron, who conveyed herbal secrets to his human pupils and taught Achilles to use yarrow on the battlegrounds of Troy.[61]

A bunch of 50 yarrow A. millefolium subsp. millefolium var. millefolium stalks, used for I Ching divination

Yarrow and tortoiseshell are considered to be lucky in Chinese tradition.[62]

The stalks are dried and used as a randomising agent in I Ching divination.[63]

In the Hebrides a leaf held against the eyes was sometimes believed to give second sight.[64]

In Sussex and Devonshire superstition, yarrow was used for finding one's real sweetheart. One would pluck yarrow growing on a young man's grave while reciting:

Yarrow, sweet yarrow, the first that I have found,
in the name of Jesus Christ, I pluck it from the ground;
As Joseph loved sweet Mary, and took her for his dear,
so in a dream this night, I hope, my true love will appear.

and go to sleep with the yarrow under the pillow.[60]

In a similar tradition in Wicklow, girls would pick yarrow on Hallow Eve and recite:

Thou pretty herb of Venus' tree,
Thy true name is yarrow;
Now who my bosom friend may be,
Pray tell thou me to-morrow.

then retire for the night without speaking and go to sleep with an ounce of yarrow sewn in flannel under the pillow.[60]

In Suffolk a leaf was placed in the nose so it would bleed, while reciting

Green 'arrow, green 'arrow, you bears a white blow,
If my love love me, my nose will bleed now;
If my love don't love me, it 'on't bleed a drop,
If my love do love me, 'twill bleed every drop.[60]

In Dublin on May Day or the night before, women would place a stocking full of yarrow under their pillow and recite:

Good morrow, good yarrow, good morrow to thee,
I hope by the yarrow my lover to see;
And that he may be married to me.
The colour of his hair and the clothes he does wear,
And if he be for me may his face be turned to me,
And if he be not, dark and surely may he be,
And his back be turned toward me.[60]

In the witchcraft trial of Elspeth Reoch in March 1616, she was alleged to have plucked "melefour," thought to be another name for yarrow, and said "In nomine Patris, Fiili, et Spiritus Sancti" to become able to cure distemper (disorders of the four humours) and impart the faculty of prediction.[60]

Yarrow was thought to bring luck due to being, according to one woman cited by James Britten, "the first herb our Saviour put in His hand when a child."[60] This is apparently a corruption of the Achilles myth.[19]