I think I'm going to have to take exception at your initial premise that nursery owners and "profiteers" are intentionally misinforming customer about plant hardiness zones. And I will also take exception that this zonal information is pretty much useless.

First, the USDA hardiness zone system is based on a system of climate mapping first developed by Henry Skinner in 1960 when he was head of the National Arboretum, in conjunction with the American Horticultural Society. It was later amended, further developed and published by the USDA. It has nothing to do with farmers and annuals but was indeed intended as a guide for home gardeners. And a guide is all that it is intended to be. Anyone who has gardened for any length of time should have come to a rather quick realization that there are few, if any, absolutes in gardening and winter cold tolerance is certainly not one of them. All sorts of other factors come into play on how well a plant will withstand winter cold, including snowcover, rainfall, plant provenance, drainage, altitude and winds, how long established and of course, individual microclimates. And summer heat factors also have a bearing on winter hardiness - in some cases, plants are unable to withstand 'normal' winter temeratures without damage because they were not exposed to sufficient heat during the growing season to sufficiently ripen new growth.

Personally, I think your rant is rather misplaced. Rather than obssessing about record low temperatures or the evil intent of nursery owners to rob you by recommending plants ill-suited for your area, develop a thorough understanding of your garden and the climate it displays. And do your research on the plants themselves to understand the growing conditions they require, as they often have a far bigger effect on winter hardiness than do minimum temperatures.

Oddly enough, I find most hardiness information, both on nursery tags and in published references, to be on the conservative side rather than overly optimistic.

Ditto GardenGal's comments.

To me the bottom line is not to be afraid of failure. Certainly you don't want to be removing a lot of huge dead trees from your garden after a hard winter. Some ideas are also just plain unrealistic (like the guy who expects coconut palms to grow in Seattle if he just keeps on trying - ha.) But plants will always perform better or worse than expected and there will always be pleasant and unpleasant surprises after a hard winter. To me, if my gardening style isn't flexible enough to account for those surprises and absorb a certain degree of risk, that takes a lot of the fun out of it - especailly as there are so many cool plants that are hardier than many nurserymen and books realize.

A lot of useful weather data can be found at the Western Regional Climate Center: http://www.wrcc.dri.edu/Climsum.html
The information necessary to calculate your USDA zone isn't provided, but what is provided is a more complete climate picture that is at least as useful, including record lows, averages, precipitation, etc. I haven't looked at the weather.com site but their numbers sound suspect to me. The WRCC data is from official NWS records. Olympia's all time low was -8F on January 1, 1979. Klamath Falls appears to be -17F in 1972.

(Interesting side note - according to the Oregon Plant Atlas (google it), madronas can be found as far up/inland as the Crater Lake area (as is chinkapin) - I'm sure plants of that provenance would do fine in Klamath Falls.)

You're certainly right about microclimates - they are much more variable than people realize, even over very short distances. When you find the all time record low for your area, it might not necessarily represent you. A fine example is the Olympia weather station, whose very cold winter temperatures don't really represent the rest of the area. I can tell this just by looking at some of the plants around town (eucalypts etc) after a hard winter. When I lived on the north side of Olympia, I usually had overnight temperatures 10-15 (in one instance 20) degrees warmer than those recorded at the airport during those cold arctic events. Another example of this sort of thing was during the Feb 2006 freeze when in the same night, Tacoma Narrows airport had a low of 32F and McChord, a short distance away, bottomed out at 12F.

thanks for the reference to the climate data. i'd like to know how the oregon plant atlas gets it information, because it seems way too cold up in Crater Lake for Madrone's to survive; it would be amazing if it was true. Other maps I have found show madrones around crater lake, but its gotten down to -21 up there, and it averages 18 degrees during the night for 4 winter months, and only gets up to 69 during the hottest month. maybe this weather station for the national park is in some weird place.

I don't see where the hardiness zones have anything to do with farmers who plant annual corps. Those crops are planted after the hardest part of winter and then harvested before winter. There are so many micro-climates in this region that the only way to get info for long term gardening is to set up your own min-max recording thermometer and a rain gauge. Both are inexpensive. Tom

There are also madronas in Washington surprisingly far inland and high up at one place I know of near White Pass.

The Oregon Plant Atlas web site says this:

Distribution data for the Atlas mapping program are based on vouchered (records that are derived from herbarium specimens) and unvouchered (ones that do not have a collected specimen; i.e., taken from an observation for a species list) records. These are clearly distinguished on the maps. Species lists are contributed by individuals, the Native Plant Society of Oregon, governmental agencies and other organizations. Vouchered records were generously provided by the following herbaria:
Albertson College of Idaho CIC
Bureau of Land ManagementBurns Dist BLMB
Bureau of Land ManagementÂCoos Bay Dist BLMC
Bureau of Land ManagementÂLakeview Dist BLMLK
Bureau of Land ManagementÂMedford Dist BLMM
Central Oregon Community College COCC
Eastern Oregon University EOSC
Harvard University GH, A, AMES, ECON
Lane Community College LCEU
Linfield College LINF
New York Botanical Garden NY
Oregon State University Herbaria OSC, ORE, WILLU
Portland State University HPSU
Southern Oregon University SOC
University of Washington WTU
USFS Northeastern Oregon Herbarium BAKER
Utah State University UTC
Washington State University WS

Bottom line is, if you want plants GUARANTEED to not die in the winter, you need either of two kinds:

Locally native plants,

or

Plastic plants.

Or, move to the tropics, where there is no winter.

Gardening is life itself in a nutshell. There are no guarantees in life, beyond death itself.

Do you have any idea how time consuming and expensive it is to collect and store long-term weather data? And what is long-term anyway? where record winter low temps are concerned, that might mean collecting and storing records, minute by minute, for over a century. We didn't have that kind of technology a century ago. And who cares anyway?? Stick with natives if it worries you that much. They've been tested over millenia, no thermometers necessary.

Hardiness zones are offered to you, free of charge, as a guide with which to explore the world of gardening. It's up to you to make use of them, or not, as you see fit.

The confusion comes in thinking that they are guarantees, or absolutes. And I do not agree that absolute record low temp is of any use, for these reasons: we only know for the period for which we've collected and stored data (last few decades at best), and how often does that occur anyway??

Now duration of low temps would be interesting to know but again that would be complicated to collect and calculate and report so don't worry too much over it.

Gardening is a life lesson. There are no absolutes and no one's going to hold you by the hand and lead you around all the pitfalls.

All plants do have an ingrained minimum temperature below which they start to die. However, as mentioned specimens in an immature condition (growth not fully hardened) are likely to be damaged above that point. And some species, gums (Eucalyptus) for instance vary markedly in hardiness from one individual to the next, when raised from seed. This is one of the advantages of clonal cultivars, propagations of such are all fragments of a single genetic individual of known hardiness (when its hardiness is known).

USDA is annual average minimum for 15 years. Temperature spread indicated for each zone doesn't reflect record lows. Those wishing plants to be most reliable should choose those rated for next zone below theirs, as is often suggested in discussions of zones - including, I think, that generated by USDA.

Native plants may also be damaged by hard winters, 1990 for instance burnt native broadleaf evergreens (madrona and salal) in Seattle and even killed native stand of Ceanothus velutinus along 405 in Bellevue (a few have reappeared there since, possibly from seed).

Sometimes I put in a plant with a Z9 hardiness rating that costs me whatever dollars. I have a friend who says to me, '' It's gonna be a heartbreaker'' Cuz it will prolly die in the winter.

Yet how often do we justify let's say a concert ticket for $60, or $100 plus for the dubious honour of getting less than 2 hours from the main performer and a half hour intro set from someband that really should be busking on the street??

And that Z9 plant lasted in my garden all summer providing me countless hours of joy in my garden

...Don