"In antiquity, yarrow was known as herbal militaris, for its use in staunching the flow of blood from wounds. Native Americans had many uses for the plant, including pain relief, fever reduction, and blood issues of all kinds. Yarrow grows up to 3500 meters above sea level. The plant commonly flowers from May through June, and is a frequent component in butterfly gardens. Common yarrow is frequently found in the mildly disturbed soil of grasslands and open forests. Active growth occurs in the spring.
This plant is extremely easy to grow, but looks best with regular water. It easily reseeds though it can be aggressive." -calscape.org