The last couple of weeks have been cold in Karuizawa and no roses, or tulips have even formed buds and tree branches are bare of even any leaves. This place really should not be open as it's just a bunch of brown spikey branches right now. Very scary. Recommend phoning around mid May to see if the situation has changed.
Also, if you do go it's best to drive car. The bus only runs once an hour max.