kitchen garden vs garden

kitchen garden and garden both are nouns.

Word	Noun	Adjective	Verb	Adverb
kitchen garden	Yes	No	No	No
garden	Yes	Yes	Yes	No

As nouns, garden is a hypernym of kitchen garden; that is, garden is a word with a broader meaning than kitchen garden:

kitchen garden (noun)	garden (noun)
a small garden where vegetables are grown	a plot of ground where plants are cultivated
	a yard or lawn adjoining a house
	the flowers or vegetables or fruits or herbs that are cultivated in a garden

kitchen garden (adjective)	garden (adjective)
	the usual or familiar type

kitchen garden (verb)	garden (verb)
	work in the garden