USDA Plant Hardiness Zones - a primer

Here's a great primer explaining the USDA Plant Hardiness Zones via the University of Minnesota Extension Service. There has been much talk of late of how plant hardiness zones may be shifting. This explains the system and how the Twin Cities is still pretty well-rooted in Zone 4a, even though we have many adventurous gardeners tempting fate and living life on the Hardiness-edge!

USDA Plant Hardiness Zones revisited