arboretum vs orchard

arboretum

noun
  • A place where many varieties of tree are grown for research, educational, and ornamental purposes. 

orchard

noun
  • The trees themselves cultivated in such an area. 

  • A garden or an area of land for the cultivation of fruit or nut trees. 

How often have the words arboretum and orchard occurred in a corpus of books? (source: Google Ngram Viewer )