We had a freakishly warm winter (winter by the calendar) and several days in the 80s as winter came to an end (by the calendar). The we hit a cold three weeks, temperatures closer to normal for early Spring here in Z5. So far awhile Spring was colder than Winter. Then it warmed a little and then it turned cold. For two days running  we had nights close to freezing. No damage to plants, though all had dropped their winter hardiness and budded, fooled into thinking real Spring had arrived. Last night, somehow, frost got a few young hosta leaves. Which is about right for this time on the calendar. The average day for the last frost here in mid-Iowa is usually listed as May15. So we're not safe yet, as the hostas discovered. That is, if we're back to normal. We'll see.