What effect will freezing temperatures have on newly emerged perennials?

Question:

Will newly emerged perennials be seriously harmed if they begin to leaf out and are then subjected to freezing temperatures?

Answer:

Some perennials emerge early in the spring.  In Iowa, it’s common to have relatively warm days in early or mid-March and it is equally common to have below freezing temperatures in April or even early May.  In most cases, early leaf growth on bleeding heart, hosta, columbine, catmint, and other perennials will be just fine with cold temperatures.  If temperatures are cold enough, especially below 26°F to 28°F, then damage could occur.  Freezing temperatures may damage or destroy the newly emerged foliage of perennials, however, their roots and crowns should be unharmed. The damaged perennials should send up a second flush of growth in a few weeks. Good care in spring and summer should help the perennials recover.