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USDA Hardiness map outdated?

Posted by neonrider 8A (Sunset-31) (My Page) on
Fri, Jan 21, 11 at 10:18

This winter (2010/2011) (I live in Zone 8A) so far we did not have anything below 17F (couple of nights only) and the rest was 20F or above (nights only), which I consider mostly zone 9A weather with two nights into z8b, so basically where I live is about 20 miles south of the z7b "border" yet we are having mainly z8b weather most of the time, while temps below 15F are rare here. Wonder if the USDA zone maps are outdated by now. I know it is not global warming, because I looked up historical data and temperatures here 20-30 years ago used to be even warmer than now.

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RE: USDA Hardiness map outdated?

I think you're probably on to something since when I plug in my ZIP code the USDA map says I'm in Z5b but the U.S. National Arboretum map and GardenWeb both put me in Z6a. Typically we see a few nights when the temp dips down to minus 9 or 10, maybe even minus 12 once in a green moon but it isn't the AVERAGE winter low.

My neighbor three houses to the north insists his garden is Z5b but he's going by the fact it gets far enough below zero once a year to hit the Z5b low temp.

Someone on the Winter Sowing forum posted a link to a site called PlantMaps and that one has a zoom feature so you can punch in your ZIP code and get a close-up view of the USDA map. Naturally, when I zoomed in on my ZIP code, it showed me in Z5b.

I'm also going by a few Z6 plants that self sow in my garden. If I'm Z5b, they shouldn't come back each year but not only do they come back, they're growing in the cracks in my concrete breezeway.

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