The best (USDA) zone map I've ever seen!

Skybird - z5, Denver, ColoradoJanuary 18, 2011

Hi All,

I just found what might be the best zone map in existence! In the past I've always had a problem with being able to tell just exactly which zone stopped where and which one started where---you could never "get close enough" to be really exact. While that may not make a lot of difference in much of the country, out here in The West, where a couple miles can make a BIG difference, it MATTERS!

The map linked below is INTERACTIVE, and you can zoom in as close as you want to, to see what "they" say is your zone! I think we all agree that there's an "arbitrariness" about zones, and the USDA zone system only takes into account absolute temperatures, but ya gotta start somewhere! I know our hills and valleys and sun and wind still make a LOT of difference, but with this, at least we can actually do more than guess at what the USDA thinks we are!

If you go to the Home Page, you can click on individual states---or you can put in your zip code and ZOOM right in on yourself! You can also zoom in to wherever you want on the U. S. map, and if you do it that way, you can click on the individual "zones" on the left and top, and they show up on the map as you click (or unclick) them!

It's fun to play with, if nothing else!

No more looking at "that" old USDA map and going: Let's see! I THINK I'm about here!

Happy lookin',


Here is a link that might be useful: USDA Interactive Zone Map!

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treebarb Z5 Denver

Things were king of quiet here when you weren't posting as much. I'm glad you're back in full force.
This map is very helpful. I just went through it quickly, will spend more time with it tonight. I've always been curious why Greeley, 30 miles north of me is so much colder than Denver. I figured it was because of the Platte river. I will be exploring that. The plant zones should be fun to check out, too.

    Bookmark   January 18, 2011 at 8:33AM
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Great Skybird! A map that doesn't require a high-powered magnifying glass . . . and doesn't tax those of us with poor color vision too much.

I wonder where their stats come from. The weather service has the numbers for, at least, the last 20 or so years on just about everywhere. It would take some work to put it all together for the US but, I trust that was what was done.

Oregon State University had some kind of federal grant to create an updated USDA map. That was my understanding anyway. Something happened to all of that effort during the brewhaha over climate change and no hardiness map came of it.

If you search for the results of the OSU work you end up being directed by NASA to a private sector outfit that sells maps, many including the years up to 2000. However, the map for growing degree days, stop at 1980! Wonderful when information get plugged in a policy pipeline!

Anyway, here are the OSU maps. I find the "Mean/Median length of freeze-free period" (at the very bottom of the page) to be very relevant in comparing gardening climates.


    Bookmark   January 18, 2011 at 11:24AM
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Great links thank you both! xo, Jilly Billy

    Bookmark   January 18, 2011 at 5:54PM
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mtny(SW MT zn 3)

interesting map , but i noticed data only utilizes data from 1960's through about 1990 I would be very interested in seeing the map beng worked on

    Bookmark   January 18, 2011 at 5:59PM
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Dan Staley

I don't see the data constraints on the website. Perhaps they are using the 30-year climate trend baseline ending in 1990s (which likely will be updated soon as the 2000s were warmer than 1990s, and 2010s will be warmer than 2000s...).


    Bookmark   January 19, 2011 at 10:34AM
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mtny(SW MT zn 3)

Dan when you enter your zip and animation comes up the paragraph below.... it states use of data for 1961-1990 so yes most likely based on 30 year trend...however this summation is of of data which is still 20 plus years out of date...and the last 20 years are of the utmost interest to all of us....

    Bookmark   January 19, 2011 at 11:05AM
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Dan Staley

That's the standard 30-year reference period many orgs use, including the GISS/NOAA, to compute departure from mean/anomaly.

I agree that having the last 20 years would help, and the dataset analyses that have, say, X year smoothed trend are more useful for gardeners,

but I don't think statistically we can include the last few years in a standard 30-year trend.

Hereabouts, last year we hit our average lowest lows, but this year not close, and I just voted to have our Metro District's landscaper pay mid-4 figures to water our landscaping as soon as weather's best to pay attention and take good notes when you are pushing your frost dates & overwinter crops.


    Bookmark   January 19, 2011 at 11:54AM
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While it isn't interactive, has an updated USDA hardiness map that uses data up to 2006. Available at the link below.


Here is a link that might be useful: arborday hardiness map for 2006

    Bookmark   January 20, 2011 at 12:46AM
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dsieber(z5 (Lakewood CO))

Shoot.. I am 2 miles from the 5a and 5b aqua/light blue area. I guess it the increased altitude but that does not make sense I thought cold air sinks . Downtown Denver usually is colder than the suburbs in the 6000ft region.

    Bookmark   January 20, 2011 at 8:51PM
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Skybird - z5, Denver, Colorado

No fear, Dsieber! Remember the zone designations are really just a Jumping Off Place to get you in the Right Neck of the Woods when you're looking for things to grow! There are so many variables, that it's all pretty much a guessing game. There's the fact, as others have said, that the USDA map is old, and we've been warmin' up in recent years, there's the terrain in your immediate area, and then there's Digit's "growing days," which, I think, have more to do with food crops than with flowers!

This map shows me in 5b, but I don't even bother with the a/b part since it's such an imperfect "science!" I just think of myself as being "in" zone 5---and then it doesn't take much at all for me to try things that are "said to be" zone 6 plants----and, well, it it's something I REALLY want, I'll even try zone 7 things occasionally! And besides how imperfect the map itself is, there's also the quandary of what "zone" any particular plant actually is anyway! If you pick a specific plant and start looking around, chances are you'll find people with all sorts of different ideas of what zone it'll grow in---like the Crocosmia that came up on another current thread! Good luck finding any consensus about what zone that one is!

So go with your z5, and then go out and buy yourself some z6 things and find out what happens! Experimenting can lead to all sorts of worry-------and LOTS of fun!


    Bookmark   January 20, 2011 at 9:44PM
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The map really is awesome. It puts me in zone 5a and like dsieber, I am 1 or 2 miles from the climate change line. Of course, I had to compare the temps and such in the two areas and, honestly, the map shows a 1 degree difference between the two. The bigger difference is the precipitation which is 3 inches more in the 5b area than the 5a. I also have to note that the 5b goes through Peyton and into Elizabeth, which anyone who is familiar with the area would have to question the b, but they are the ones with the "facts" that are 20 years old. I never though 5b would go through Peyton, I thought it was just the Arkansas river valley that would get such a warm designation.


    Bookmark   January 21, 2011 at 11:10AM
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I like this little animation. But remember that hardiness zones are for winter weather, so they only give a rough estimate of summer conditions.

Here is a link that might be useful:

    Bookmark   July 14, 2011 at 12:04AM
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jnfr(z5b CO)

And even in our solid 5b zone, an unusual cold spell can happen every decade or so. It says we go to -15 and most years we don't even get that low, but I've seen temps down to -35 in Denver since I've lived here. There are always outliers.

That said, I think most plants I lose in the winter are due to dryness more than cold.

    Bookmark   July 14, 2011 at 2:15PM
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kimka(Zone 6B)

For much greater accuarcy and more scientifically based, check the new USDA Plant Hardiness Zone Map at

Here is a link that might be useful: New USDA Plant Hardiness Zone Map

    Bookmark   January 26, 2012 at 11:15AM
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jnfr(z5b CO)

Yeah, that map shows us now in zone 6. But as variable as Colorado weather can be, those averages are only a small part of the story.

    Bookmark   February 6, 2012 at 11:25AM
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