Which map should you follow?
New plant-hardiness map is causing debate while tempting Minnesota gardeners
Gardeners have long chosen plants based on the USDA Plant Hardiness Zone Map, last revised in 1990. The National Arbor Day Foundation (NADF) recently issued a new hardiness zone map based on 15 years of minimum temperatures. It reflects warming trends across the nation and moves Minnesota into warmer zones. The following maps show the differences between the USDA Plant Zone Hardiness Zone Map and the National Arbor Day Foundation Map.
Mary Meyer and Nancy Rose, Extension horticulturists, suggest you use a conservative approach to choosing landscape plants based on the new map. If you want to experiment, start with herbaceous perennials or small shrubs. If colder winters return and kill these plants, the plants can more affordably be replaced than larger, long-lived plants such as shade trees and evergreens.