Yarrow is a member of the Asteraceae or Compositae, the Aster family. It blooms in July and continues until the frosts. We harvest the flowers for medicinal preparations, although the leaves are excellent as well. If given any type of cultivation or fertilization, Yarrow really takes off, producing huge corymbs of flowers in white, light and electric pink. I prefer the white for medicine.

Elemental associations: Water
Phytochemistry: Essential oil (azulene), flavonoids, tannins, bitter principles (D. Hoffmann)
Actions: Antiseptic, anti-inflammatory, vulnerary, diuretic, astringent, diaphoretic
Specific systems: Skin, urinary tract, circulation

The name Achillea comes from the legend that Achilles, hero of the Trojan war, used it to heal the wounds of his soldiers in battle. Indeed, it is probably the best vulnerary we know, serving to instantly stop bleeding and to disinfect even a horribly deep wound. It is always a good idea to carry Yarrow if you are out hiking or far from home.
It has a particular power to curb inflammation and pain in the urinary system, and is used for infections of the prostate or the urinary tract to this end (and also because of its antiseptic and diuretic actions).
As a remedy for fever, it combines especially well with Elder flowers in the form of a hot infusion, take often, until the fever subsides.
Traditionally, Yarrow has a famous history as a plant with the power to unlock the psychic mind. It was eaten or placed under the pillow, at first bloom, for prophetic dreams. The flower stalks are dried and used to cast the I-Ching, the Chinese oracle called The Book of Changes. Perhaps this power is related to its ability to loosen, or unblock, internal stagnations (it is especially good for stagnant blood from old wounds, often colored purple under the skin) in the whole body/mind: as we know, our psychic powers are merely forgotten or repressed.

Indications: Wounds, urinary infections, fevers, blood stagnation, clairvoyance
Contraindications: Discontinue use 1 week before surgery; any herb can be habit-forming if used to excess
Preparation/Dosage: The hot infusion, 3 TBS per quart of water, is the traditional preparation. Alternatively, a tincture can be made from the fresh flowers, 33% alcohol, 1:3. Take ½ to 1 tsp. per dose, every hour in hot water for fevers.

Size: 1 fl oz