In addition, yarrow , possibly because of it's strong odor, was sometimes called the Devil's Plaything and associated with witchcraft and evil.
Another perspective asserts that yarrow could protect one against that very witchcraft. It was strewn across the threshold of a house to keep out evil influences and was worn to guard against evil spells. Some people tied sprigs of it to a baby's cradle to protect the infant from witches who might try to steal away its soul. Essentially it's a pretty little trinket whatever the lore is.