I grew up in north Alabama and always described the area as 7b. It is now rated 8a.
My prediction was true!
There’s a whole pocket of 9a around Seattle now, this was all 8b in the 2012 map:
It’s sad to see your seasons changed after half your life you were used to getting cold snowy Christmas’s now most the time we are wearing shorts and t-shirts and 70s. I’m holding out hope for a mini ice age at this point.
Winter 1966 in February we had a snow and ice storm that formed icicles on the power lines. Schools shut down and we stayed home and made snowmen. March 12 1993, we had a blizzard that made snowdrifts up to 12 feet deep. We haven’t had that much snow in a lot of years. We had a snow and ice storm February 2021 that put 4 inches of ice, sleet, and snow on the ground. We haven’t had a snowy Christmas in more years than I can remember.
Plantmaps.com has record highs and lows by date. Although the USDA map has me on the line for 7b/8a, it got to -14F in January 2018. Killed mature crepe myrtles to the ground. Also froze out my greenhouse of orchids. Could not keep it above freezing.
Washington DC is now 8a.
They moved me to 9a, but let’s see if the temps prove them right, because the low of 15 last year albeit only for a few hours on Christmas would have likely killed my citrus and Avocados had I not protected them and if I trusted the weathers low of 34 I wouldn’t have protected them.
Looking at the local ACIS data, I’d known my spot was at least just in 6a instead of the previously mapped 5b, but it looks like it’s pretty much on the border with 6b now! I’d definitely believe it. The winters and summers here in southern NH are now comparable to what I grew up with in Central NJ 30 years ago.
@jerryrva @gkight the USDA maps are determined by the average annual minimum over a 30 year period, not the absolute minimum over that period. Most nurseries understand this when writing out plant hardiness zones for their varieties. If you try to apply minimum temp survived to a USDA hardiness zone, you’re going to have a bad time, except maybe in coastal areas. And of course, some areas have wilder swings from year to year, while maintaining the same average. My layman’s assessment is that the hardiness zones are most useful east of the Mississippi.
Still 4a, still should be 3b
I also wonder if the general concept of the hardiness zone is getting less useful. One of the major predictions of what will happen with a warming climate is bigger swings from year to year, which seems to be bearing out. At the very least, it might only be reliable at the whole zone level, with the a and b designations giving a false sense of precision.
Looks like my county has changed fron 7a to 7b. But… just last winter we had a low of 3F here which falls in the 7a temp range.
I the early to mid 80s… i saw -17 F here once… very memorable… have seen a few other nights in the -1F to -7F range… deer hunted with bow/arrow on some of those mornings. Beard frozen solid into a face cover toboggan.
The calculation used for hardiness zone does not care about record lows, or rather those just count as a single data point that gets averaged with the other years’ lows. To calculate your hardiness zone, you look at the lowest temperature each year over the last 30 years, and then find the average of those 30 numbers. A location that gets to 11°F on exactly half of years and only gets to 20°F on the other half of the years would be zone 8b (average of 15.5°F), even though in half the years it has zone 8a temperatures.
This is one reason hardiness zones don’t tell the whole story, but they do tell an important piece of the story (how cold it gets on average each year).
I was just replying basically this haha so arbitrary if your low will kill stuff 2 zones below what you’re rated for. But I guess it’s just an estimation for planting and it’s up to your discretion after that
In 2021, it never got below 20 the whole winter.
That’s not quite the right way to think about it. The zone rating on plants says that in most areas with that zone, it will be likely to survive most if not all winters there. So a zone 5 rated plant should be able to withstand well below -20, if accurately rated. The rating that a nursery gives a plant is not necessarily based on science, but on a combination of observation, educated guesses based on similar plants, and the whims of the seller. A nursery that is more interested in sales or overly optimistic might exaggerate hardiness. A nursery that’s more interested in customer success might be more conservative with its ratings for the same plant.
And that’s before you get into microclimates… the methodology they used for this and the previous map are better at picking those up, but there’s still only so fine-grained you can get and still have any real accuracy when you’re doing this at a continent-wide level.
My area has shifted from borderline 6B to solidly 7A, though we had a couple of night at -5 to -7 F this year.
Life would be simpler if every winter was average.
I agree. Hardiness maps are a very rough estimate of winter lows. Averages don’t mean much when the bell curve has a wide distribution of data.
I’ve recorded winter lows for the last 16 years. While the data shows an average of -4F, which agrees with the USDA zone map (our zone has remained the same for the last couple decades at 6B) there are lots of years where temps dropped far below what’s good traditional 6B rated plants (at least what nurseries rate as 6b plants).
Here is the data by winter, which doesn’t exactly match the National Weather Service data for my area, because they record temps in Kansas City, which is somewhat warmer. Plus I record the winter low, not the yearly low.
Winter low:
2007-2008 3f
2008-2009 0f
2009-2010 -4f
2010-2011 -6f
2011-2012 -11
2012-2013 4f
2013-2014 -9
2014-2015 0f
2015-2016 2f
2016-2017 -9f
2017-2018 -9f
2018-2019 -2f
2019-2020 2f
2020-2021 -17f
2021-2022 1f
2022-2023 -10f
Darn, still zone 8a.
I’m actually kind of annoyed, zone 8b is all of 15 minutes south of me now. So close, yet so far away.
What years are they using? 1990-2020? The 30 year window of their data seems fall right in between (and not including) the -30ish lows that we had in 1989 and 2021. The in-between years didn’t see lows like that. It’s based on the banana belt years for my location 