tulip bed vs bed of flowers

tulip bed and bed of flowers both are nouns.

Word	Noun	Adjective	Verb	Adverb
tulip bed	Yes	No	No	No
bed of flowers	Yes	No	No	No

As nouns, bed of flowers is a hypernym of tulip bed; that is, bed of flowers is a word with a broader meaning than tulip bed:

Other hypernyms of tulip bed include flower bed, flowerbed.

tulip bed (noun)	bed of flowers (noun)
a flowerbed in which tulips are growing	a bed in which flowers are growing