We just returned from a short trip to Boulder, Colorado, for my niece's wedding. The parents of the groom hosted two lovely events at their beautiful home in the country outside of Boulder. Of course I was immediately drawn to their vegetable garden. It is so much more advanced than mine! But that is not surprising, since they started planting in March, and I barely had anything in the ground in late April. Imagine my surprise when I plugged their zip code into the USDA map, and found they are in exactly the same zone as me, 5B!
They are swimming in beautiful summer squash, while mine barely have 4 leaves.
Their beets are the size of baseballs, while mine just have taproots.
Carrots are huge, mine tiny.
Their tomatoes look like mine in August.
Onions dwarf mine.
Their kale does not seem to mind the 90 degree weather. I wonder if I can grow California poppies?
So I'm going to think more about the variables other than zone. It makes sense that no matter how cold it gets in the winter, it is important how quickly winter goes, and how soon it arrives.