gardener vs horticulturist

gardener and horticulturist both are nouns.

Word	Noun	Adjective	Verb	Adverb
gardener	Yes	No	No	No
horticulturist	Yes	No	No	No

As nouns, horticulturist is a hypernym of gardener; that is, horticulturist is a word with a broader meaning than gardener:

gardener: someone who takes care of a garden
horticulturist: an expert in the science of cultivating plants (fruit or flowers or vegetables or ornamental plants)

Other hypernyms of gardener include plantsman.

gardener (noun)	horticulturist (noun)
someone who takes care of a garden	an expert in the science of cultivating plants (fruit or flowers or vegetables or ornamental plants)
someone employed to work in a garden