Reply #14: The Arborday maps mainly reflect winter low temps

[NickB79]

I've been using Arborday zone maps for years to grow trees and shrubs up here in Minnesota, and each zone I've seen corresponded to a specific winter low. Zone 4a means you can expect a winter low of -30F on a fairly consistent basis, while zone 5a means you can expect a winter low of only -20F, for example. Winter temps have always been the main factor, and I've never read rainfall totals being a factor used for zones. For example, on the map, it now shows that parts of the central Great Plains are at a higher zone than central Minnesota, yet I know that we receive far more precipitation here than in Nebraska.