Quite a while ago, someone emailed me, asking what was a cold climate. I never did answer them, because I thought it was obvious. A cold climate is any climate too cold to grow the plants you really want to grow. If you live in Austin, and you want to grow pineapples outdoors, obviously your climate is too cold. If you live next door to me, and you want to grow crape myrtles; sorry, you live in a cold climate.
When I started this website, I defined a cold climate as USDA Hardiness Zone 4, because it got down to -30F (-34C) in the winter here. No, not the whole winter–three or four days here, a week there–just enough to kill Zone 5 plants. And as I thumbed through catalogs and consulted reference books (this was before there was much on the internet), it seemed to me there was a big dividing line between Zones 4 and 5, that quite a lot more plants could take Zone 5. It was difficult to find good information on cold hardy varieties, and techniques and tricks to help plants survive, and I wanted to collect the information I found in one central location.
I’m not such a stickler on my definition anymore, in part because I’ve learned that many factors contribute to a plant’s hardiness, and minimum winter temperature is just one of many things to consider, and also because, heh, I no longer live in a cold climate by my own definition. Yes, the coldest it’s gotten this winter is a balmy -4F(-20C), which is Zone 6! The last time it got colder than -20F(-28.8C) was in 2005, so it’s been warmer than Zone 4 for the last three winters.
Meanwhile, in Iowa (and elsewhere) it’s gotten much colder than typical. Seems to me, in these days of global weirding, we need to learn from each other more than ever. What do you think is worse, unusual cold or unusual heat?