rockery vs rock garden

rockery and rock garden both are nouns.

Word	Noun	Adjective	Verb	Adverb
rockery	Yes	No	No	No
rock garden	Yes	No	No	No

As nouns, rockery and rock garden are synonyms defined as:

rockery and rock garden: a garden featuring rocks; usually alpine plants

rockery (noun)	rock garden (noun)
a garden featuring rocks; usually alpine plants	a garden featuring rocks; usually alpine plants