Thanks, something odd to me though, I'm 7a, 10 miles north of me is 8a. But I have had frosts plenty of times when they didn't have them north of me.

Well, according to that map I'm about 2 miles inside 6a instead of 5b.

at the end of the day it is only a guide same as the climatic zoning, one needs to take into account, from coast to coast aspect of land quality or other of soil and micro climate, none of that can be grid map plotted. nothing is set in cement when it comes to nature.

another not considered is the rain channels, rain is not always all over here we had good shower of rain 1 kilometer away as the crow flies got none.

len

Here is a link that might be useful: lens rural dreams essay

Len, are you suggesting that soil type has an influence on minimum average air temperatures? Doesn't seem likely to me.

Well, my part of maryland looks right to me. Wertach, there's a good little essay in Shep Ogden's Straight Ahead Organic which is called How I Moved North and Got Warmer. He moved 100 miles north and got a hardiness zone warmer due to the specifics of local geography. You mightlike to read it, if you happen across the book somewhere. It's pretty neat.

Pat, Dark soils that are dense might absorb more daytime heat and then release it to the surface at night better than loose soils because the looseness doesn't conduct the heat back upward as quickly at night. Now this just applies concerning frosts in spring and fall.
I don't see so much difference in winter especially with snow cover.

If black graphite is spread on top of snow, the blackness absorbs heat and will melt snow more quick;y. Some think that even an invisible coating of soot on polar snow and ice is contributing to melting more than otherwise.

So perhaps a very dense dark soil, like a plowed field without snow cover, at the winter minimums might cause a slightly warmer air temp than over say a grass-covered field. If there were no wind, no snow, etc. If there were such a difference it would be extremely tiny.

Definitely only a guide. I live in 8b, but according to the new map just a few miles south is 9a. I have micro-climates in my yard, so it's safe to say my yard has a combination of both.

Thanks for the update. I now feel justified. For the last several years, my zone "9a" shown above was an overide to the "official" USDA zone classfication of 8b. My 9a is now in agreement with the new map.

I'm not sure why people are confused by living near another zone, maybe because they are now making "official" the variations that locales can have?

Where I grew up it was well-known that north of us and west of us maybe 5-7 miles was 2-3 weeks behind us, but 20 miles east of us was 2-3 weeks ahead. We were on a plateau between the Catskills and the Hudson River, all this in one county. If you looked on a USDA hardiness map back then you would have guessed all the area was zone 4, but bordering 5 fairly closely. Now it shows where my parents live to be 5b, north and west is 5a, and east is 6a. It seems like the map is getting more accurate with increased data collection.

Back to Pat...If you've ever seen the heat waves glimmering off a dark and bare field on a hot spring day, you can see that the field is absorbing more heat than grassy or light colored soils or surfaces. Stones and water are champion heat absorbers..though wet soil takes a tremendous amount of heat to warm up.

Now back to the regular programming.

The Washington Post's story on the new zone maps says "The sophisticated gardener can't just rely on the zone map, and what's the fun of that?" said Todd Forrest of the New York Botanical Garden (now in the same zone as Washington). "If you can't plant things you're not supposed to grow, you're not having fun as a gardener."

New plant map shifts area to warmer zone - The Washington Post

I have moved from zone 4b to 5a, yahoo!

4b is now 20 miles to the north.

Dean

I note that the map averages temperatures 1975-2005. But we are in 2012, with temperatures rising rapidly. My zone 6 has not experienced sub zero temperatures since, I think, early 2009. We have had no frost after April 15 in the last two years, and no October frost either.

That snapshot is or will be obsolete soon, and those zones are now further North than the map indicates. This winter here in SE MI has been a regular zone 8 winter so far, with just one night of temperatures around 5F. Forget Goldrush apples, I should consider getting a couple fig trees.

It was much colder last winter here in MD, but it rarely gets that cold in my now 5 years out here.

I do like the fact that the new map lets you get results for a specific zip code. However, I wouldn't get too excited about any apparent zone increase. Keep in mind that the low temps listed are an average, and some winters will get lower than that. Just West of me is now listed as 5a, but they get about 5 degrees colder than my part of 5a... which puts them closer to 4b, where they were previously listed. So IMO, take these "increases" with a grain of salt.

I wouldn't rush out to buy fruit or nut trees based upon the higher numbers, and have them die in 5-10 years during a below-average winter.

Of course, just like the old chart, the winter hardiness zones have no bearing on vegetable gardening... where this is posted. ;-)

Re: the Goldrush apple, what really got me over the edge is the fact that a friend in upstate NY (colder, wetter than here) is getting good apples out of that tree, he says with time to spare before the first hard freeze. Re: melons, it has always been a combination of not liking to spray and iffy weather. This year is going to be spray, black mulch, and trust in global warming (I am also fencing the new orchard, so what's a man to do with all that fenced land? Melons, butternuts, and all sorts of shelling peas and beans, all those things that I usually discard on efficiency grounds). Re: figs, I will wait another decade...

Well that's interesting...they've moved me from 6a to 6b, but I'm still in 4a, in real life, since -27 F doesn't seem to be in the zone 6 categories! LOL

USDA's zip code search says I'm still in 7a, but I live in a large zip code, and I'm toward the southern edge of it.

The jury's still out on this one....

Lots of interesting comments here, but to me the salient issues are these:

1) this is a map based on statistical averages. It does not take into account the fact that every piece of ground is subject to the effect of microclimates. Elevation, latitude, topology, soil type, proximity to water, and existing vegetation - even man-made structures - all affect the POSSIBILITY of reaching the temperature parameters that define a particular zone.

2) Weather, and more importantly climate, are complex studies, and subject to variables still poorly understood. It is well known, for instance, that the earth has experienced different cycles of warmer-than-previously and cooler-than-previously, but the cause and timing of those cycles is rarely clear - the effects of a volcano, or a meteoroid hitting the earth can account for some cooler periods, but the cause of many of the cycles is still conjecture. Right now, we seem to be in a warming trend, and many climate-change deniers point to that as evidence that mankinds' influence on the atmosphere has no bearing on the global warming issue - the debate rages on. For the most part, the natural cyclical changes, and to a lesser degree, I believe, global warming, are incremental, they happen over relatively long periods of time, and will not soon affect the likelihood of anyone successfully growing more tender crops on a regular basis.

3) As zeedman points out, and some orchardists clearly grasp, this is a map of winter low temperatures; as such it is most useful in predicting the odds of perennial plant survival, and is of less utility to those who are planning their annual garden. First and last frost dates, precipitation, and wind maps are equally important when a gardener is trying to integrate climate statistics into a coherent garden plan. The gardening activities most immediately concerned with this map are structural ones concerning perennial crop placement, hardscaping, and mulching, and very little to do with the choice of which variety of annual to choose.

4) The best guide to hardiness is the native ecosystem in your specific locale. Being familiar with the native plants, watching for bud formation on local trees, new green growth in the woods, even the activities of wild animals and birds, is often a far more reliable indicator of current weather trends than human predictions based on statistical charts. As mentioned above, these are guidelines, useful for planning purposes, but no guarantee of future performance.

Well, Phil probably saw his shadow so it's back to uh..winter.

Europe, Asia, and Alaska have been cold while eastern USA is warm. At a given time there is just about so much heat in the earth.

I keep fantasizing about using a ground-source heat pump and buried pipes to create a year-round frost free soil in unheated hoop houses. It's still a little hard to justify in Maine, but for a slightly more southern locale, as the technology gets more affordable, I predict we'll see it soon in commercial production.

Here is a link that might be useful: Ground-source heat pumps