go to seed vs weaken

go to seed

verb
  • To deteriorate; to decline into an unkempt or debased condition. 

  • To pass from flowering or ripening to the formation of seeds. 

weaken

verb
  • To become weaker or less strong. 

  • To make weaker or less strong. 

How often have the words go to seed and weaken occurred in a corpus of books? (source: Google Ngram Viewer )