March 1, 1996
The ability of a tree or shrub to survive an Iowa winter depends on the seasonal change in its metabolism to a quiescent or dormant state known as acclimation. The first stages of acclimation are induced in early autumn by exposure to short days and nonfreezing chilling temperatures, both of which combine to stop growth. But to survive the kind of low midwinter temperatures recently experienced in Iowa, woody plants must be exposed to temperatures at or below freezing for some time before they become fully acclimated.
In early February 1996, record low temperatures were set in many portions of Iowa. Temperatures of -30 F or below were common, particularly in the northeast where -46 F was reported at Decorah. Although the bitter cold came at a time when most fruit crops should have been at or near their maximum hardiness, such low temperatures approached or dropped below the maximum hardiness of many perennial plant species grown in our climate.