When are the bulb fields in bloom?
When is the flower season and are the bulb fields blossoming?
From the end of March until the second week of May, the bulb fields are blossoming. The exact period in which they are blossoming obviously depends on the weather, but in general you have a great chance of encountering a blossoming field in the second half of April.
More information: http://noordwijk.org/en/sight/549/keukenhof.html