WOW! I think the Arbor Day Foundation's maps show a definite warming trend. If you look at the high-resolution maps, you can see that Utah's small zone 7 area has expanded quite a bit. Maybe I am a 7 now. They also show Utah's zone 4 area has disappeared, retreating to the north.

I noticed on the winter sowing forum, though, that someone who works for USDA was critical of the Arbor Day map, saying USDA looked at a longer time frame (30 years instead of 15) for the map they will update later this year. But hey, if climate change is happening, the past 15 years would be different than the previous 15. Anyway, let's keep our eyes out for the new USDA map when it's released.

Here's a link to the Arbor Day Foundation map.

Here is a link that might be useful: Arbor Day zone changes

I'm an architect+landscape architect. I was working at a firm in North Carolina in early 2001, and I was doing some internet searching for plant hardiness when I ran across an updated USDA Hardiness Zone map, on the USDA website. It was labeled 'preliminary', but it definitely showed the bands moving north. They also posted the old one, from 1990, and just to see for sure I toggled both in my browser, back and forth, back and forth. The bands moved north and south, north and south. I remember being so alarmed that I printed 11x17 color blow ups of each and posted them on the refrigerator in our office. What a fool. I should have sent them to the New York Times. After that I got all caught up in 911 and ended up eventually moving to Utah. I never kept those images. In 2003 I went searching for the new zone map again, but I couldn't find it. I looked everywhere on the internet and in professional journals, but the only thing I could find was a reference to an update that was "yet to be released". Why was it released in early 2001 and then pulled? It seems only now things are coming out again. The data needed to generate these climate zone maps are gathered over a long period of time. Decades. The data for the 1990 map had been collected since the 70s. Somehow we managed to shift an entire climate zone in 10 years. This scares me.

Here is a link that may be interesting:
http://faultline.org/index.php/site/comments/going_to_extremes/

Hello

Many people don't give a lot of credence to the Arbor Day zone map because it's based on only a decade or so of data. We may be close to zone 7 for lows, like it shows, but this December is a good example of daytime highs not being any where near a true zone 7.

I remember seeing the preliminary USDA map and seem to recall it being pulled for that exact reason.

I'm not trying to be a bearer of bad news but, being one who tries growing everything from palms to eucalyptus to bamboo to cacti to yuccas etc., I think the Arbor Day zone map gives us a false sense of what we can do here without winter protection.

Alan