Hi Lizy,

Most of the Denver Metro area has been considered somewhere
in zone 5 ever since I moved here—in 1964! BUT, with climate change in recent years, some of the area has been
changed from 5 (a or b) to 6a—I don't think they're showing any of us in 6b
yet!

Here's the "climate change updated" USDA map where
you can look up what THEY think you are!
Their newest map is interactive (finally!), so you can zoom in as close
as you need to.

http://planthardiness.ars.usda.gov/PHZMWeb/InteractiveMap.aspx

But 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.

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—but
then it doesn't take much at all for me to try things that are "said to
be" zone 6 plants—and, well, if it's something I REALLY want, I'll even
try zone 7 things occasionally! And
besides how imperfect zone maps are, there's also the quandary of what
"zone" any particular plant actually is anyway! If you pick any specific plant and start “researching”
it, chances are you'll find people with all sorts of different ideas of what
zone it'll grow in! Even some very
common things, if you look on different sites, you can find them listed as
anything from zone 4a/b to 6a/b.

There are so many factors that affect temps in any one neighborhood,
yard, or even the small micro climates within a yard, so look up what the USDA
says and then have fun playing! I’m
still “officially” considered to be z5b, but there was no “a & b” back in
the 60’s, and I got used to, and still do, think just in terms of being zone 5,
which means down to -20°. Then when I
find something I WANT that’s z6 or warmer, I just try it! I have things that are almost always
considered to be z6 that grow easily, and there are other things I’ve tried
that were marginally z5—that died!
Besides temps it depends on soil, water, sun, wind conditions—and more. And even if “they’re” right about which zone
I’m in, there are always the winters “like last winter” where we went from a
very long, VERY warm fall and then suddenly dropped down into single digits,
and all the plants that weren’t even thinking about going dormant yet
DIED! It’s sorta all called
GARDENING! ;-)

Here’s the USDA page that explains the factors that go into
their zone designations—and some other stuff!

http://planthardiness.ars.usda.gov/PHZMWeb/About.aspx

I can’t imagine NOT gardening—even tho I know some things
are gonna die on me!

Skybird

Cities are "heat islands" that will raise your zone number because of things like buildings and paved roads will absorb and trap daytime heat and prevent nightime lows from dropping as much. So, I THINK areas of downtown Denver are zone 6 whereas most of us in the surrounding suburbs are zone 5.

I've always considered my area a zone 5. Like Skybird, I don't bother with the a/b. I have no idea and it doesn't seem to matter much when it comes to purchasing plants.

My mom just moved here from Las Vegas and she has had a difficult time adjusting to the annual/perennial thing too. Many things that grew year-round in Las Vegas are either annuals here or you have to over-winter them somewhere inside or in a microclimate.

Of course, there are surprises along the way. I met a guy recently who leaves his Cannas outdoors all year. He has some microclimate at one corner of his house where they can survive in the ground and come back in the Spring. Not me. I have to parade mine into the garage every Fall and back out again in the Spring and hope for survival.