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Wednesday, April 23, 2008

Hardiness Zone Map is being updated!

If you've been looking at plants wishing you were just one zone warmer, guess what! The hardiness maps are changing! Later this year, the USDA will release a new hardiness map. The new map is rumored to include 15 zones instead of the current 11, and the a and b sub zones may be eliminated.

The current USDA map, produced in 1990, is based on average temperatures from 1974 -1986. The new map will take advantage of the increased weather data and computer modeling that has become available during the last 20 years.

I don't know what the new USDA map will look like, but the Arbor Day Foundation has produced their own updated map (shown below). You can see that the update has put many areas of the country into a warmer zone.

Personally, I view the zones as guidelines and generally have no issues with planting tropicals that are listed as requiring one zone warmer than my (currently!) USDA Zone 7 garden. I just put them where they get the most sun and mulch them well. Zone maps are based off just a snippet of time in the history our constantly changing planet, and while it looks like Earth is heating up now, it wasn't too long ago (climatologically) there was the "Little Ice Age"!

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