Ashikaga Flower Park is insanely awesome for its massive and numerous wisteria that bloom from late April to mid-May. It also has colorful azaleas and rhododendron. Eye-popping flower park with ponds and flowery walking paths. Nicely landscaped. Must be one of Japan’s grandest gardens for wisteria. Opened in April 1997. Admission during wisteria season is most expensive at ¥1,700.
Lower photo is the “Giant Wisteria” (大藤). The trellis is huge and the wisteria strands are very long. Super-duper awesome. The Giant Wisteria extends over 36 meters by 33 meters (!). About the same as a large hotel ballroom or a whopping 600 tatami mats. The trellis was only 50 tatami mats when it was first transplanted here. Unbelievable. 
More Ashikaga Flower Park photos: https://photoguide.jp/pix/thumbnails.php?album=849
Nearest train station is Ashikaga Flower Park Station on the JR Ryomo Line. From Tokyo, take the train at Ueno Station and transfer at Oyama Station. Or you can go from Asakusa Station, slightly faster and more expensive. Takes about 2 hours either way.