It's open about 50 days between April and May and ...

It's open about 50 days between April and May and you can see the tulips in the field only for about two weeks. Needless to say, timing of visit has to be perfect for that. Nonetheless, the tulips also bloom in the garden in case you miss seeing the field. And, it's worth the visit even then.
Amsterdam Pass is the best way to visit if you don't want to stand in line for the tickets for a couple of hours.
Worth the visit.