green fingers vs long suit

green fingers and long suit both are nouns.

Word	Noun	Adjective	Verb	Adverb
green fingers	Yes	No	No	No
long suit	Yes	No	No	No

As nouns, long suit is a hypernym of green fingers; that is, long suit is a word with a broader meaning than green fingers:

Other hypernyms of green fingers include forte, metier, speciality, specialty, strength, strong point, strong suit.

green fingers (noun)	long suit (noun)
a special ability to make plants grow	an asset of special worth or utility
	in a hand, the suit having the most cards