What is the collective noun for tulips?

There isn't a specific collective noun for tulips in common usage.

While we might say "a bouquet of tulips" or "a bed of tulips," there isn't a single word like "a flock of birds" or "a herd of cows" that describes a group of tulips.

You could creatively use "a display of tulips," "a patch of tulips," or "a field of tulips" to describe a large gathering of them.