Demystifying USDA Zone Hardiness Maps

I searched around here and elsewhere online and never got a straight answer to this question: what information does a USDA hardiness zone really tell you? Allow me to explain what I mean. I'm here in Minneapolis, MN but we are thinking of moving up north, which is zone 3. We have our reservations because there are many plants that we want to grow which are not suitable to that zone, such as almonds which are stated as zone 5 minimum. Does this mean I will never be able to grown an almond tree, or just that almonds don't grow well? I've seen people grow all kinds of stuff when I lived in Fairbanks, AK (zone 1 or 2 depending), so I'm skeptical of what zones actually mean. Should I let these maps affect me or should I just go for it and maybe graft some almonds onto some hardy stock or something? It's intimidating to see so few extremely useful plants in zone 3 and so many plants I want to grow in zone 5+. Sure, we could move, but we are rooted here and let's just assume that's not an option. I hear of micro climates/ sun traps and what not as well, but is that reliable?

Another thing is that the only maps that I see online are recent as of 2005, using 1976-2005 data. With climate change, I'd be much more interested in 2004-2014 data, you know? Is there any way to generate maps using specific parameters? Maybe northern MN isn't even zone 3 anymore...

I mean, we want to be successful growing nut trees as staple crops, but we also want to get out of the cities. A majority of stuff I've seen on permaculture has been for warmer climates- what's a guy to do?

New maps have been released recently. http://planthardiness.ars.usda.gov/PHZMWeb/

Zones are based on if the plant will survive the low temperature of those zones.

If you are planning a move to zone 3, I would suggest taking a look at St. Lawrence Nursery in upstate NY.
They are in zone 3, and therefore specialize in cold winter hardy fruits and nuts.

Their shipping season has ended, so they have taken down their catalog from their site.
I'm hoping that in the autumn, when work slows down around their nursery, they will update their catalog.
http://www.sln.potsdam.ny.us/pg.html

Thanks for the updated maps. Is there anywhere to get information on just the recent data though? Not that 2012 is non-recent, but since climate change is warming up most zones, it seems that if we include the older data, we will get a lower zone than what is actually the case because it was much colder back then.

Also, we've all seen plants that are supposedly zone 5 yet are growing in zone 3 or less, so I know they say that it is the temp that plants will no longer live at, but I'm just confused because it seems to not be the case. How strict are the zones, then, might be another way to phrase it.

Everyplace has micro climates. So your zone 3 property could have sections that stay much warmer and also sections that get much colder. Where I am my property mostly stays much warmer because it is on too of a hill and all the cold air flows down and collects at the bottom. My soil hardly froze last summer but at the bottom of the hill the ground was frozen solid for almost a month. Also the zones don't say how much rain you get or what summers are like so there will be plants rated for a zone that might need different summer temperatures than you will get or more or less rain. I think the ideal thing is to be in the property experiencing the micro climates and also if you want to you can create micro climates. If you want to grow something that needs more warmth grow it up higher and maybe have large rocks around it to absorb heat from the sun and make it warmer that way too.

Some web pages tell me I am zone 8b and others say zone 10 or even 11. Really my property has lots of different areas with a wide range of temperatures in winter.

It is not entirely dependent on how low will they go.
For instance, a plant might be rated to -20.
It can go from +20 in the afternoon to -20 in the wee hours without a hitch.
That same plant could go from +50 in the afternoon to -10 in the wee hours and die.
Sudden changes are far more damaging than slow steady changes.

Also, the physical health of the plant is important.
Two plants of the same species, side by side, but one of great vigor and the other suffering any type of malady.
The healthier plant would survive a much lower temperature than would the weaker plant.

USDA says: "The zones in this edition were calculated based on 1976-2005 temperature data. Each zone represents the average annual extreme minimum temperature for an area, reflecting the temperatures recorded for each of the years 1976-2005. This does not represent the coldest it has ever been or ever will be in an area, but it reflects the average lowest winter temperature for a given geographic area for this time period. This average value became the standard for zones in the 1960s."

So the only information going into the maps is minimum temperature. Data is also only fine down to a square 1/2 mile on a side. I suspect that I have at least two zones on my property, possibly three. If you are determined to have almonds, and willing to put in some effort, and have a few failures, I expect you could grow them.


Thank You Kindly,
Topher

some gardeners and plant geeks swear by the SUNSET zone maps, instead of the usda zone maps. if you want to look into it, here's the link:

http://www.sunset.com/garden/climate-zones/climate-zones-intro-us-map


find plants for your area:
http://plantfinder.sunset.com/plant-home.jsp

i cannot even imagine living in zone 5 (usda) forget about zone 3, but i guess i am spoiled and acclimated to mild winters.

but that map above gives me more info than just living in zone 8(usda), by that one i am in zone 7, but its a whole different system. it considers rainfall amounts, average high temps, and some other stuff instead of just average lows.

sometimes you see people reference that one, saying sunset zone ____ instead of usda zone ___ but its not as popular so theres not as many people talking about it.

trees may survive the winter but
frost free days and summer warmth are important if you want ripe fruit and nuts

http://www.cals.uidaho.edu/edComm/pdf/BUL/BUL0867.pdf
http://www.garden.org/ediblelandscaping/?page=october_nuts

Almonds (Prunus spp.)
Almond trees can grow where peach trees grow. They make attractive 15- to 30-foot tall-trees. However, they bloom very early, often with the first warm spell in February, so many times the crop is lost due to a late spring frost. This has restricted the commercial almond industry to the West Coast and protected areas. The fruit looks like a green peach, but it's the nut inside you want. Some varieties are self-fertile


you pays your money and takes your chances

As a fellow Minnesotan I can give some advice here I think.

I'm zone 4, almost 3, but i love trying to grow everything "exotic".
My garden is only a few years old, so plants/trees are relatively young still.
Do your homework, look for cultivars that boast "most cold hardy", but from multiple places.
Plant in protected spots, use microclimates, protect from wind, and try to keep trees from emerging early.
You'll have some things die, some things die back but grow, some grow but not fruit every year, etc, but it's worth it in my opinion.
Keep an eye out for natural "survivors" locally, and depend on tried and true stuff for your main crops, etc.
Oikos tree crops, badgersett, and St lawrence have good cold hardy stuff.
Maybe stick to tried and true for main crops :Apples, aronia, seaberry, bush cherry, pie cherry, and blueberries are really tough.

I've had hybrid hickory, walnut, hardy pecan, and hybrid chestnut make it several years(and through our horrific winter this past year), but no nuts yet.
Also Paw paw, american persimmon, jujube, hardy kiwi, sweet cherry, plumcot, plum, pear, schischandra, grapes and black berry all mostly rated for zone 5ish survive with some mixed results fruiting.

Unfortunately one of the things that's died on me is peach, which is similar to almond so you may be out of luck there.
Good luck, keep us posted