Are USDA zones correct??

[FigTreeJunkie]

According to the USDA map, I am at the 6a/b border. Looking over historical data from the past few years, it looks like I am more in the 7a zone, and maybe 7b given the temperatures have not gone below 5F in a few years.
I haven't researched this too much. Does anyone have any idea if/how the zones are changing?

[jrdewhirst]

Last two winters have been ridiculously warm. Here -- a little bit south of you -- the lows were 10-15 degrees F above normal. It could be a random variation. It could be a very rapid onset of global warming.

Be careful what you wish for re climate change. We'll probably never get extreme heat or drought as in the western U.S. More likely hurricanes that uproot trees and knock down houses.

[Sod]

I’m in the same boat as Joe. The last 2 or 3 winters have been a full zone increase into zone 9 territory for me. It may go back even further, I haven’t looked. There are a ton of microclimate pockets in this valley, so it’s hard to tell what’s normal and what’s an environmental change. We still don’t get enough heat long enough to ripen figs we should be able to because of the temp swings and oddball frosts.

[Otis]

I know there are many localized microclimates in every USDA climate zone, but I agree things are getting weird with what's going on out west, in Europe and China. I believe they could predict weather more accurately 20 years ago than now, and I'll bet it'll get even more unpredictable in the future.

[batty]

They will probably update the zone map again soon.., I believe current map is from 2012, and actually uses data averages from 1976-2005. It's definitely not 1976 anymore.

I looked at my temp data for the last 20 years and it put me about a half zone warmer than what the USDA has. But that's just on average - we're all still at risk of a random arctic blast!

[KDAD]

While winter survivability matters to me though with most trees in pots and those in-ground protected anyway the zones kind of become irrelevant. I'm with Sod in that a longer growing season with temperatures consistently above 70F and sufficient sunlight to ripen figs matter more to me. Would a GDD chart be of greater benefit to us than USDA zones?

[Sod]

I think the GDD helps form a better picture if you keep it conjunction with temps above a certain range, but that’s a bigger discussion.

[KDAD]

And maybe we need to worry more about the average high temperature not the low?

[jessup42]

KDAD thats a scary thought but you might be onto something!

[PacNorWreck]

Just remember that USDA zones are calculated based on average extreme minimum temperatures, meaning the lowest temperature reached per year on average over a long period of time. While climate change will mean that we all will likely continue to see our zones increase over time, it’s a slow process due to the averages. Seattle has reached 15 degrees at my house for at least an hour in roughly half of the winters I’ve lived here with the past few winters being more like 20-25 - 8b / 9a implies average extreme minima of 15-25 degrees, so overall it’s pretty accurate even if it doesn’t feel that way most of the time.

[FigTreeJunkie]

The average minimum temperature seems to be rising at about 0.03 F per year since 1895, but closer to 0.5 F per year since 2011 (yes, I know... smaller sample size....).

[Tongalahi]

The zones are based off of 20ish year averages, last one was taken in 2006 I believe and the one before that in 1990. They’ve already shifted in that time period and I think they’ve shifted again but we won’t get an updated map until 2026-2030 or so. Here is a link that illustrates the change from 1990 to 2006
https://www.arborday.org/media/mapchanges.cfm

here where I live I think the past 2 years have been more like zone 7a as well, I’m in SE Michigan near the lake and the last two winters have been very temperate where most days were in the 20’s and 30’s and nights dropped to the tens and the absolute low was about 0F

[CaricaChris]

I'm at the border of 7a/7b. Last 2 winters were 8b, but the two years before that were 7a. The zones aren't usually off by much. I took the extreme lows for my area from 2011-2020 and it worked out to be like 6.6°F on average, which is 1.6° warmer than USDA's average using older data. An increase no doubt, but not as extreme as what others seem to report.