old man's pepper vs soldier's woundwort

old man's pepper

noun
  • Achillea millefolium or common yarrow, a flowering plant native to temperate regions of the Northern Hemisphere. 

soldier's woundwort

noun
  • Achillea millefolium or common yarrow, a flowering plant widespread in the temperate Northern Hemisphere, formerly and sometimes used to stanch the flow of blood. 

How often have the words old man's pepper and soldier's woundwort occurred in a corpus of books? (source: Google Ngram Viewer )