Several Perennials Lost to Winter Kill

I lost quite a few perennials over winter this year. Some were well-established plants and others were rated as hardy for the area (zone 5). What did I do wrong?

You did nothing wrong. You, many other gardeners, and professionals (myself included) lost an interesting variety of perennials. Some hardy and even a few native plants died while other, what we thought less hardy, plants survived. In speaking with other horticulturists we can not find a common thread or pattern to the winter kill. I think the combination of hot dry summer weather followed by a cold open winter may have been too much stress for some plants. In any case it is a good reminder that despite our best efforts a challenging growing climate can always leave us surprised. Try to look at your plant loss as opportunities to try something new the next season.