poor man's soap vs summersweet

poor man's soap

noun
  • Synonym of summersweet (“Clethra alnifolia”) 

summersweet

noun
  • Clethra alnifolia, a deciduous flowering shrub of eastern North America. 

How often have the words poor man's soap and summersweet occurred in a corpus of books? (source: Google Ngram Viewer )