New USDA plant hardiness map released

I find it interesting that people see this as alarmist. It's simply data, sourced from GIS provided through ESRI, if I'm reading the USDA correctly. You may not like the data, but it's simply data. The map, according to the USDA, is based on 30-year averages (1991 to 2020) for the lowest annual winter temperatures. It also incorporates more details from thousands of new data collection stations that have been added to collect data, as well as more detailed mapping technology (GIS). What you're seeing in detail is because of those new sensors in more areas and more detailed mapping. Some of the areas are certainly startling (I have a hard time believing that Arlington is Zone 8 for instance), however, I have also found that people have a really skewed perspective of local weather and misremember stuff (tell me for instance, when your first frost was last year--the year before, five years ago) Some of the zones and quirks may have been there all along and weren't noticed much, as well.
 
They are claiming 7a for me but I am in the Shenandoah Valley a stones throw from West Virginia (6a). Unquestionably the weather has mellowed out a bit, but I can't get that 3 days of 14 below zero about 5 years back. I love the idea of zone 7, but I live with the reality that it is a generalization. One thing I have noticed over many decades, and more in recent years, the more they talk about the weather, the more apt they are to be wrong.
 
rockm said:
I find it interesting that people see this as alarmist. It's simply data, sourced from GIS provided through ESRI, if I'm reading the USDA correctly. You may not like the data, but it's simply data. The map, according to the USDA, is based on 30-year averages (1991 to 2020) for the lowest annual winter temperatures. It also incorporates more details from thousands of new data collection stations that have been added to collect data, as well as more detailed mapping technology (GIS). What you're seeing in detail is because of those new sensors in more areas and more detailed mapping. Some of the areas are certainly startling (I have a hard time believing that Arlington is Zone 8 for instance), however, I have also found that people have a really skewed perspective of local weather and misremember stuff (tell me for instance, when your first frost was last year--the year before, five years ago) Some of the zones and quirks may have been there all along and weren't noticed much, as well.
Click to expand...
I always like ( or almost always) the cool logic of your responses even when I don't agree. And certainly almost all people do hold false memories. Interestingly, my wife has a weather log that tracks every weekday of the weather in mid Fauquier County for the past 33 years. Funny thing is, she actually may be a bit more like you and still we have found common ground.
 
penumbra said:
They are claiming 7a for me but I am in the Shenandoah Valley a stones throw from West Virginia (6a). Unquestionably the weather has mellowed out a bit, but I can't get that 3 days of 14 below zero about 5 years back. I love the idea of zone 7, but I live with the reality that it is a generalization. One thing I have noticed over many decades, and more in recent years, the more they talk about the weather, the more apt they are to be wrong.
Click to expand...
The data is averages. One period of extreme cold, or five periods of extreme cold, over the last 30 years aren't going to shift things much. Winters have been getting warmer, despite occasional (and sometimes memorable) bitter cold.
www.wunderground.com

Warmest Winter in U.S. History So Far

The nation's first two months of winter were the warmest in more than a century of recordkeeping.
www.wunderground.com
 
Just like others have said, the update shows the general warming trend. Not accounted for in the zone definition is the short-term variability in temperature. We have had members here observing that, in their own locations, they have seen variability that wreaks havoc in the dormancy patterns of trees and causes loss of crop or even deaths of trees.
For me, the variability means that I have to plan the protection for my trees better.
 
As rockm points out, the map is based on 30 years of AVERAGES. One of the facts of climate change is that more extreme weather events become more frequent, but the overall trend is warmer. These extremes can greatly effect plant hardiness. For example, the last few winters in my area have been warmer BUT with sudden extreme lows that severely damaged species considered hardy in 8b. Among landscape plants, I have cut about a dozen common exotic species from my plant palette. Cold hardiness is also affected by extreme heat during the summer, leaving plants in a weakened state and therefore more vulnerable to sudden extreme cold during an otherwise warm winter.

Hell, in Texas we can't even keep the power grid working in the summer or the winter.
 
rockm said:
I find it interesting that people see this as alarmist. It's simply data, sourced from GIS provided through ESRI, if I'm reading the USDA correctly. You may not like the data, but it's simply data. The map, according to the USDA, is based on 30-year averages (1991 to 2020) for the lowest annual winter temperatures. It also incorporates more details from thousands of new data collection stations that have been added to collect data, as well as more detailed mapping technology (GIS). What you're seeing in detail is because of those new sensors in more areas and more detailed mapping. Some of the areas are certainly startling (I have a hard time believing that Arlington is Zone 8 for instance), however, I have also found that people have a really skewed perspective of local weather and misremember stuff (tell me for instance, when your first frost was last year--the year before, five years ago) Some of the zones and quirks may have been there all along and weren't noticed much, as well.
Click to expand...

Well, if the posters claiming it is “alarmist” actually took the time to read the report they would see that it contains a disclaimer that it is NOT intended to be evidence of climate change/global warming:

“Climate Change
Climate changes are usually based on trends in overall annual average temperatures recorded over 50-100 years. Because the USDA PHZM represents 30-year averages of what are essentially extreme weather events (the coldest temperature of the year), changes in zones are not reliable evidence of whether there has been global warming.”

Seems like the opposite of “alarmist” to me.

But if one wants to make everything into a government conspiracy, “you do you” 🙄
 
As far as overwintering bonsai or species choices, I'm not changing anything. In reality, our zones didn't just jump this past year. These are based on 30 year moving averages (the prior 30 years before the map came out) - so data from a single year is 1/30th of the picture. There will still be warmer than average and colder than average years in the future (but probably more warmer ones than colder ones on the whole).

It still just takes one bad winter or one very early/late hard freeze to drive us bonsai nuts crazy though.
 
Kanorin said:
As far as overwintering bonsai or species choices, I'm not changing anything. In reality, our zones didn't just jump this past year. These are based on 30 year moving averages (the prior 30 years before the map came out) - so data from a single year is 1/30th of the picture. There will still be warmer than average and colder than average years in the future (but probably more warmer ones than colder ones on the whole).

It still just takes one bad winter or one very early/late hard freeze to drive us bonsai nuts crazy though.
Click to expand...
There should be zero surprise here. We are nuts by membership.
 
pandacular said:
Interesting to see that Seattle is now 9a. You can really see the urban heat island effect in the Puget Sound (though I'm sure there's more to it than that).

Makes me feel a bit safer with my Azara microphylla that's sitting on my roof.
Click to expand...
Just goes to show that it's only relevant to cold hardiness, despite our tendency to use it for heat as well. I'm in 9a here in Houston.
 
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