If you want to see as many hydrangea varieties as possible, covering several diferent shapes and the whole (pastel) rainbow then Hase-Dera (near the Daibutsu) is the place to go. If, on the otherhand, you want blue blob overload then Meigetsuin (yesterday's photo) is not to be missed. Expect queues at both places.
[jules' pics] Amadeus the Amaryllis
23 hours ago