Generally with Yukon Gold you want to wait until the vines die back because they are keeper not new potatoes, so I wouldn't disturb them until then. When the plants get about 14-16 inches high hill them either with soil or straw up to half their height. If they keep growing taller, hill them up more. The last thing you want is green potatoes. (the green part is poisonous- night shade family). Old times say that you should leave keepers in the ground up to two weeks after vines die back, but as long as they are mostly dried up you should be fine. After you dig them let them dry off well before you store them for the winter. Note potatoes need regular watering from the time they start blooming until they start dying back, if you want a good harvest.