USDA zones are useful in deciding what perennials will survive in your locality. Since most vegetables are annuals, it is not very useful. It is based on the average winter low temps. It simply means that the average low temp is Z8a is 5 degrees Fahrenheit lower than Z8b. Vegetable growers need to concern with length of growing season, average summer temps etc. On the west coast Z 8a extends into Canada, but the growing conditions for vegetables are much different than for middle Georgia.

I was in 5B until the new maps came out and now I'm 6A. Not thrilled to be moved up, as it means any plant that is hardy to minus-19 is safe to grow. I'm not that old but I can remember two nights in the mid-70s when the official low was minus-25 and out in rural areas minus-33. I would have preferred going by the worst-case scenario. If my plants are cold-hardy to minus ten and our average annual low is -8, I'm not feeling bad. But if our record low is minus 18, then I better not plan on preserving that plant.

Mike

My house is in 6B but my primary garden is in 7A and the southwest garden is a 7B. ;) Seriously there are so many micro-climates on my property that we may have 4 or 5 different zones covered.

I agree with Farmerdilla - garden zones are just a very general guideline only and their practical applications are limited. Nice to know but not something to lose sleep over. If you want to be much more specific then use the Sunset Gardening zone maps.

Dave

It would be nice if everyone identified which STATE they lived in. A zone 6 in the PNW is not the same as a zone 6 in Ohio. I hate it when I click on a cogent post by someone to look at their "home page", only to find that they live in "the U.S."

That's really helpful.....not!!!!!!!!

"It would be nice if everyone identified which STATE they lived in."

I've suggested this in the recent past but it seems to not register. It's not really hard to put your name and state at the end of your post, I do it all the time.

Greg
Southern Nevada

Yo up front.

Curt

Mike
Cincinnati, OH

Home of the 2010 Central Division MLB Champs

I got an error on the site you posted.
I was an 8(ish), then went up to a 9(ish) during the drought, but were probably a 7(ish) this summer of no sun!
Who knows???????? NT

USDA Hardiness zones are not gardening zones. Farmerdilla explained it. The link in the original post explains it. USDA Hardiness zones tell us the average annual coldest temperature in a given area. They are not related to frost dates, day length, degree days or the amount of rain an area normally gets.

"It would be nice if everyone identified which STATE they lived in."

Some people are just too paranoid for that. They think the boogie man will find them.

True, the USDA Plant Hardiness Zones are designed for arborists and perennials. BUT, there is a trick to the zones, many people don't know. The zone number designates the approximate number of months you will have frost free on average.

For example:
Zone 3a = at least 90 days frost-free.
Zone 3b = at least 105 days frost-free.
Zone 4a = at least 120 days frost-free.
Zone 5a = at least 135 days frost-free.
Zone 5b = at least 150 days frost-free.
Etc, etc...
Zone 11a = at least 335 days frost-free.
(This is why Florida oranges occasionally freeze!)
Zone 11b = at least 350 days frost-free.
Barring a natural disaster or nuclear winter Zone 12 never freezes.

Now, of course there is much more involved in a plants success than just frost dates. For example, you might be in zone 9 in Phoenix, but good luck getting vigorous growth for all of those (approx) 270 days. That's why the American Horticultural Society Heat Zone system was created. AND, since frost and heat are not the end-all-be-all of a plant's potential success, the Sunset Climate Zone system was developed, which takes into account things like precipitation, wind, humidity, etc.

If you combine all three...
Sunset Climate Zone
USDA Plant Hardiness Zone
American Horticultural Society Heat Zone
And do a little research about weeds & pests, it is possible to find the ideal gardening climate!

HINT: Gardening is often easier overall, in locales that have at least some Winter. Say, two months of freezes to keep weeds and pests at lower levels.

Class dismissed!

Sunset Climate Zone
USDA Plant Hardiness Zone
American Horticultural Society Heat Zone
And do a little research about weeds & pests, it is possible to find the ideal gardening climate!

That is why all that is in my name line right at the top.

Another thing I don't see mentioned to help out for gardening is microclimate. And season extension. Here on the Front Range it is very easy to extend the season a month (provided you anchor against the tremendous wind in spring).

Dan

Some people are just too paranoid for that. They think the boogie man will find them.

Don't even JOKE about the boogie man. The boogie man will get you. I'd go into more detail but I'm concerned that I may have said too much already.

{{gwi:115965}}

4b.... :-(

It's sure pretty, though!

Zone 3b, two weeks ago... :o(
8^(
{{gwi:112057}}
September 17th, 2010 14:27

I knew I was in 6, but the another zone finder I found with zipcode said 7, this zone finder says I'm in zone 6b, I agree with that for Northwest Tennessee.

[[[.... zone number designates the approximate number of months you will have frost free on average.....Zone 5a = at least 135 days frost-free.]]]]

I wouldn't count on that in every location. Last freeze here was June 15, first freeze was the end of August. So 2 1/2 months of no freeze in Zone 5A.

That's a longer growing season this year than usual, since we almost always have snow for the 4th of July.

I count on 70 days and start plants indoors. Sometimes we get lucky. I still have tomatoes. It froze and then went back up to 80 degrees. It's supposed to freeze next week, though, so I need to get the tomatoes covered. I've never had tomatoes into October before.

It boils down to knowing your local weather.

Note: I find that the zone hardiness for plants is often way off. I'm getting fruit off of trees only rated to zone 6.

The USDA Zones are said to be valid only for the eastern half of the US.

Mike

I confuse the boogie man by gardening on the border. (And, ignore winter hardiness zones for the purpose of vegetable gardening.)

Yes, the cold of winter has very little to do with the growing season.

The frost-free period might be "averaged" but that isn't very useful. If we average something that is already a broad-brush designation - things can get a little meaningless.

For purposes of growing season comparisons, weather.com will give you "average weather" of each month's temperature and precipitation for most cities in North America and major cities, worldwide.

For the heat needed for plant growth, the Weather Service provides that information for selected US cities (linked below).

Steve

Here is a link that might be useful: Total Growing Degree Days (Corn)

I'm so confused....which is why I'm keeping a veggie garden journal of what I planted/when/how it did/how long it lasted. I figure in about 15 years I'll know what I'm doing.

Dan may have put all the info in his line, but I have no idea where he is. What is AHS?

I've always been told the USDA is what you go by.
My area (No CA, the real wine country NOT NAPA!) has so many micro- climates it's crazy!
This year was so cold, I would have put us from a zone 9ish, down to a zone 7! NO sun this summer!

Don't even JOKE about the boogie man. The boogie man will get you.

Ain't skeered. You should go see a psychiatrist.

. . . but, the Hardiness zones are for Winter, not Summer!

Steve

It says I'm Z6A. I'm leaving my zone as is. I live in a hilly area of NY and have had killing frost on one part of my property and tomatoes untouched on the other. Too many micro-climates to contend with.

Jane
Westchester County, NY

The heat-zone map is interesting. Note that it tracks number of days OVER 86; it isn't an indicator of how many days come close, necessarily. For example, here on the northeast coast we are an AHS heat zone 3 or even maybe a 2, not many days per year over 86. This summer I remember only a couple. But we always get many days in the low 80's and there are a lot of nights that stay warm - sweet potatoes do well here with no special help. Contrast that to the to the same "heat" zone in northern Vermont where growing sweet potatoes would be like rigging a circus event.

So again it is tracking average extremes - extreme daytime high for the yearly cycle rather than extreme nightime lows as the cold hardiness zones do.

To me, I use the USDA zone not to determine the average amount of Frost Free Days or the total Growing Degree Days but what the coldest temp over the last X number of years has been.

In spring I don't transplant sensitive plants until after May 15, give or take a week based on weather forecasts. That's because in the vast majority of years after the Ides, it doesn't get lower than 40 degrees. But it has been 32 degrees as late as May 25.

When it comes to GDD, much depends on how they are measured. Some groups use 50 degrees as the base, other 55. Some cap the high temp at 85, 90 or whatever - some do not have a cap. Others use a very basic calculation (high temp + low temp divided by two then subtract the base) to arrive at each days total, others use a formula where the true daily average is calculated, so that if there are 14 hours above 85 degrees, more GDDs are accumulated than if one hour it gets to 85.

Mike

The USDA hardiness zone finder says I'm in zone 6b, so the zone finder originally here on Gardenweb said I was in zone 7 earlier this year, can't get it to work or can't find the zone finder on the page they show now, but I still agree I'm in 6 somewhere.

The zone-finder is suspect. It says my area is 6a, which is definitely not the case. It hasn't been below zero in 26 years.

pnbrown, same here. I'm inside the 128 loop about 5 miles from the water and can't think of the last time we were below zero. Even that brutal (for this area) January two years ago where we never got out of the 20's never had us lower than the single digits at night.

Well, this just goes to show you how statistics work. Knowing the AVERAGE low temperatures or AVERAGE high temperatures or AVERAGE frost free days, etc., is only useful up to a point. After that you have to go by trial and error, experience, local gardening wisdom, etc. Things climatologists can't put into numbers.

This doesn't mean the science is wrong. This just means that some things are hard to quantify in a way that's meaningful for a vegetable gardener who just wants to know when they should set out their tomatoes.

Bascially, I think the zones are handy for beginners or people new to an area to get some sort of ballpark estimate of when frost will be or things like that. But there's so many more variables going on in any one garden spot that there's really no substitute for experience to fine-tune things for your own garden.

I guess I'm zone 8a. I'm in the mojave desert, southern california. You would think a desert would be in a higher zone.

"I guess I'm zone 8a. I'm in the mojave desert, southern california. You would think a desert would be in a higher zone."

I live in Southern Nevada 60 miles outside of Las Vegas and they list my zone as 10. I really don't put much faith in the zone system as our weather has been changing so much in the past two years. I've seen it down to 22 degrees before and other winters where it never freezes at all. If someone asks me what zone I'm in I say "A Hot One." Anymore it's very hard to get a handle on planting times so I just follow what's been the norm in the past and use that as a guideline.

Greg
Southern Nevada

I live in the tropics (upper region) in Australia and it's hard to find information on garden zones relative to this area as most of the Australian charts only include the lower regions of Australia. It never frosts here unless some freak thing happens, I think the last time it frosted was well over 50 years ago. I also have to cope with the tropical rains in summer and high temperatures and high humidity which doesn't agree with most of the plants I like.
I guess it could be either a zone 11 or 12, I'm not all that sure. One thing I know for sure is the bugs never stop!

As far as the Sunset Zones, they have me in the same one as Gaylord, Mi.!!! A few miles down the road south in my county they are in the same one as the Kentucky zone!!!

It's kinda like the NOAA weather report for tonight. There is a frost advisery for me, but 6 tenths of a mile east there isn't one! Well, I guess they got to draw the line somewhere.

I'm z4 to z5 depending on the year! The thing with winter temps is unless you are dealing with fruit trees, it shouldn't matter. I'm about on the line of growing peach trees. I can get them through winter and get fruit, but its very iffy and i get a lot of die back of branches. Summer is hot and humid and allows me to grow almost anything with mid May to mid Sept being my growing season (i plant a lot earlier, and have some crops go well into Nov) for the most part.

On the spring side of things, a hoophouse can really extend your growing season. By early March i was consistently in the 90F range every day it was sunny and the plants responded like crazy. Without heat my tropicals were fine down into the mid 20's (outside).

If you jump across the state and happen to grow near L Michigan around Milwaukee, your zone is very high. Last winter the coldest temp at the airport was 1F and that happened in December!

Another possibly heat rising factor is the "heat island effect"... This can clearly be seen in Minneapolis and probably inside most big cities. All that concrete that is warmed from the sun all day, releases that heat when the sun goes down. If you ever walk by a brick building in the evening on a sunny day, you can just feel the heat coming off that wall.

Low areas are usually always frost pockets. I jog at night and it can clearly be felt when you go down the hills in my neighborhood. I would say you can have 5F variations in just a short distance and with just small rises/drops.

The link below has more info than you could ever want, including controversial recent changes

The old USDA zones make no sense for vegetables here in Columbia
They put us in a colder zone, but it gets a lot hotter during the summer than in the surrounding areas

Here is a link that might be useful: USA Today--Recent Zone Maps

the area i live in here in San Francisco is cold and foggy, after the 4th of july it usually stays in the 60's or high 50's with lots of fog then just drive or walk 3 miles and its sunny and in the 70's, the weather forecasters call them microclimates, to grow anything,i usually stick to cool season vegetables and take a chance growing tomatoes, even the variety called san francisco foggy tomato does not do well, but others swear by it, go figure.i keep a garden log so i can remember what did well for the year, so zones don't work for me too many variables, happy gardening

Ugh.

I posted links to 'heat zone maps', 'freeze/frost' maps and 'sunrise, sunset' times at Maps by State.

Thanks Albert_135! That explains a lot

I see that Columbia is a highly localized "9" in the heat zone map,
while it's a "7" in the old USDA cold zone system

That's good to keep in mind while choosing plants

I've posted a link to the SC hot zone map below (because it's cool)
Columbia is the small, light yellow, bean-shaped thing in the middle of the state

Here is a link that might be useful: {{gwi:115963}}