I went to Ume Matsuri, which is the Plum Festival at Mount Tsukuba! The festival runs every year from then end of February to late March. This year, the festival goes until March 21, 2018 so be sure to check it out! The flowers are expected to be in full bloom mid March. They have events running on the weekends including performances and tea ceremonies. You can go on the weekdays as well if you just want to enjoy the beauty of the plum groves and Tsukuba Mountain. I also highly recommend going to a hot spring / onsen / bathhouse while you are there, I will link the one I went to here. It is very relaxing and the scenery is gorgeous. There are many things to do at the mountain, including Tsukubasan Shrine, little villages, climbing the mountain, taking a cable car to the summit, a high ropes course, and a ropeway going up the mountain! I also suggest trying their Plum ice cream, it was delicious!

Directions: If you are coming from Tokyo, take the Tsukuba Express all the way to Tsukuba Center, then catch the shuttle bus to Tsukuba Mountain from platform 1 at the Tsukuba Bus Terminal. The Tsukuba Express costs 1190 yen from Akihabara and then the shuttle bus is 720 yen to either Numata stop or Tsukuba Shrine.