Will Hardiness Zones Need Changing?

Started by Judy Glattstein, June 29, 2023, 11:49:38 AM

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Judy Glattstein

Not that I ever thought of hardiness zones as more than a stumbling attempt - based only on winter cold, nothing about duration, soil type, protection of reliable winter snow cover, etc. But . . .

Temperatures here in western New Jersey are somewhat moderate so far this summer while my daughter living outside Houston in Texas is enduring torrid temperatures to say the least.

Hardly any snow last winter, this summer has been dry until we were deluged with 2.5 inches of rain in less than 24 hours. And a recent nighttime thunderstorm with near constant lightening and thunder (some only 3 seconds apart = a half mile away) and rain drumming on the skylight. Power out but that's common.

So my question for those who like to speculate - are hardiness zones in need of a revision?


Judy refers to the hardiness zones established by the US Dept. of Agriculture. They were formulated with special reference to perennial fruit crops east of the Rocky Mountains, and later extended to ornamentals. Gardeners west of the plains states (the "Midwest") have long ignored them. When I lived in the foothills of the Cascade range, I was on the borderline between Zone 1 and Zone 8! Sunset Magazine offers a much more detailed map for the West, and I think it has been extended eastward in recent years; it makes sense for us. Because we all garden in microclimates, the best approach is to try whatever we like, and replace it if it fails.

Martin Bohnet

The zones work reasonably well for middle Europe, but of course borders are moving around these days, with more and more things able to survive winters - and other plants less able to survive summers - if that is what you consider revision, Judy, they'll surely need to be reassigned to some areas. The plants fitting the zones stay the same, so the interesting question is: how fast can populations follow their zones (or other descriptions of their feel-good conditions)?
Martin (pronouns: he/his/him)


Don't know...... in Germany it has become fashionable to plant exotics like ,,hardy" palm trees and Camellia which were considered tender a few years earlier. I did the same in my former garden in northern Germany. It worked very well and I saw a subtropical garden arising in my best fantasies...... until a ,,normal" winter came and wiped the dreams out. Climate change means more heat, yes, but it also means more extremes which may also be cold. With a new El NiƱo phenomenon building up we will see what it will bring to all of us.....
Algarve, Portugal
350m elevation, frost free
Mediterranean Climate


The Sunset Western Garden Book Uses 23 climate zones instead of 10 for the Western  states [as far east as New Mexico, Colorado, Wyoming, and Montana.].  Even with these refinements, I am able to consistently grow many things that Sunset suggests should fail.
Marc Rosenblum

Falls City, OR USA

I am in USDA zone 8b where temperatures almost never fall below 15F  -9.4C.  Rainfall 50"+  but none  June-September.  We seldom get snow; but when it comes we get 30" overnight.  soil is sandy loam with a lot of humus.  Oregon- where Dallas is NNW of Phoenix.