Peony buds turned to mush after one surprise frost in Zone 5

I had 30 peony plants lined up along my side fence in Des Moines, and the buds were perfect on Tuesday night. Then Wednesday morning hit 28 degrees, and I found every single one droopy and brown by noon. I panicked and cut them all down, but my aunt who grows dahlias said I should have left the stems alone because the plants still needed foliage. She was right, the roots are fine, but I lost the whole bloom season in one night. Next year I'm watching the forecast like a hawk and covering them with old bedsheets if temps dip below 35. Does anyone else bother protecting established peonies, or do you just let nature take its course and hope for the best?