A visual comparison of USDA gardening zones from 1976 to 2020
May 13, 2024 9:12 AM   Subscribe

The USDA has updated their plant hardiness zone maps. The 2012 USDA hardiness zones were calculated using the average lowest winter temperature for the observation period of 1976-2005. The new zones are calculated using the years 1991-2020. These two observation windows overlap. Colors show the difference between the two 30-year averages for each place on the map. Choose a city or region to see what's changed over 44 years.
posted by fader (19 comments total) 28 users marked this as a favorite
I'm 2.5 years in at my community garden and have been keeping an eye on this.

The NPR link above does a decent job of explaining that the USDA zone is only part of the puzzle. It refers to the lowest average temperature for winter; that dictates what plants would have a chance of surviving outdoors all winter in those conditions. Brooklyn's gardening zone actually hasn't changed on the new list.

But that's not to say that that's the only thing to consider, and it's also not the only thing that may be impacted by climate change. This zone doesn't address "how hot are your summers", and it also doesn't address "how weird is your spring". This spring here in Brooklyn has been really weird - the weather was cold all April, and then in May it's been pogo-jumping back and forth between 55 degrees and 80 degrees, and then back down to low 60s, then up to mid-70s, then down to high 50s and...yeah. I've been sitting on some seeds that I was by all rights meant to plant 2 weeks ago because the seed packet says "plant 4 weeks after the last frost" but it also says "plant when the soil is consistently above 65 degrees at night," and I have no idea whether we're there yet, but since we're upper 50s today I'd say no.
posted by EmpressCallipygos at 9:20 AM on May 13 [7 favorites]

I wish this interactive would make it more obvious that you have to scroll to see more information. It wasn't clear at first, so I was just watching that plant or whatever walking across the top of the screen for a sec, until I realized I needed to scroll down for more text blurbs.
posted by limeonaire at 9:21 AM on May 13 [2 favorites]

Do different places have differently weird springs, such that you could make a map of it? Or is weird just a property of spring everywhere?
posted by madcaptenor at 9:30 AM on May 13

madcaptenor: your question is one shared by one of the experts quoted in the little right-scrolly thing at the bottom:
One thing I’ve noticed in my horticulture career is that “global weirding” — the continental climate variability we have here — does quite a bit to negate the USDA zone changes. I always want what I can’t have and persistently have things perform well even for a few years, only to be killed in late spring freezes. A plant’s ability to prosper somewhere is based upon more than the average winter temperature (i.e., USDA zone).
– John Murgel, extension specialist for Douglas County, Colorado State University
posted by hydropsyche at 9:45 AM on May 13 [5 favorites]

I was going to post this myself! Really great interactive article that’s tailored to your location within the US. I am responsible for our yard but am an intermediate gardener at best. I learned a lot from this. I thought the zones considered summer heat but they don’t.

In central NC I’ve noticed that some annuals are becoming perennials due to the lack of hard freezes. The most obvious change in surburbia, though, is that our fescue grass does worse every year and our neighbors with heat-tolerant grasses have nicer lawns over time.
posted by caviar2d2 at 9:49 AM on May 13

This is terrific work from NPR. Being able to customize an article based on your location is a great idea and works really well for this topic.
posted by gwint at 9:50 AM on May 13 [2 favorites]

I wish this interactive would make it more obvious that you have to scroll to see more information.

Also, if you type "Saint Louis" and expect it to work, it will tell you all about Raleigh, NC. It expects "St. Louis" exactly.

My wife's sticking with the advice to keep treating this area like it's zone 6. The average might be warmer now but the standard deviation is more and spring has more temperature whiplash.
posted by Foosnark at 10:40 AM on May 13 [1 favorite]

IMO, an 'average yearly low' is not actually all that helpful. The article makes this point as well, and I honestly find it surprising that the scale hasn't been changed.

An average means that a number of low temperatures are lower than average, and it could be a large number of them are lower. With plants, a few degrees makes a real difference, so the info being provided with averages is not that valuable. It also doesn't take micro-climates into account, where the temperature can be even lower than average. IMO, the zone should instead provide the lowest lows that have ever been recorded vs the average, especially since they are already rated in a range.

Basically it means that many years plants that are rated to survive in your zone will actually die because lows are far lower than they can handle. Also, the comparison between Juneau, Boston, and Santa Fe isn't particularly valuable, because for the most part, people use hardiness ratings for gardens of managed plants, not 'greenspace' of native plants, so the amount of water a plant may receive in Boston vs Santa Fe is extremely individually variable, not necessarily just based on rainfall. So if your assumption is that managed gardens look extremely different between Juneau, Boston, and Santa Fe, that's incorrect.
posted by The_Vegetables at 11:17 AM on May 13

posted by The_Vegetables

posted by doctornemo at 12:27 PM on May 13 [1 favorite]

“global weirding” is a phrase I like very much, and want to see in greater circulation.
posted by doctornemo at 12:28 PM on May 13 [6 favorites]

I'm a bit bummed out that they were not kidding about the heat map not really being a thing - even the AHS has just an image of it.
posted by zenon at 1:56 PM on May 13

The Feds have a dynamic map down to street level, as of 2023 .
posted by BWA at 2:40 PM on May 13 [1 favorite]

Looks like the current system dates from 1960. Since it’s so widely used and is printed on every plant label, I’m sure it’s not trivial to revamp it. But I like climographs, which just show the 12 months along the X axis and two datasets along the Y: monthly average temperature and monthly average precipitation. I wonder how well those visual patterns would work. In env science we got where we could just glance at one and think “desert” or “tropical” or whatever.
posted by caviar2d2 at 3:49 PM on May 13 [1 favorite]

Glad to see this information but hate the scrolling.
After this spring-- or rather the big teaser that reverted to winter not just once, but three times-- all bets are off. My tomatoes went along quite well for two months of pampering and then died in a ridiculous May frost. It was 105 the day I got to Idaho on May 5. Idaho weather-- never predictable.
posted by BlueHorse at 7:12 PM on May 13

This is a pretty good introduction to USDA zones and the issues with them. I garden in an area where the question to "will it overwinter" is "probably not"; in my experience the value of the zone number is pretty low. Local gardens and gardeners are the best sources of information, whether that's a garden club or just looking at what it successfully growing in my neighbors' yards. Most towns around here have perennial sales in the spring where you can get divisions of plants that are tried and true locally, usually run as a fundraiser of some kind. Local growers are also a great source of info; I always get investment plants (trees, shrubs) from a local grower that specializes in cold-hardy and native plants.

Even if we are just considering overwintering, though, temperature is not the only significant factor . The past few winters we've seen a lot of really big temp swings, with a snowstorm one day, then rain, then a single-digit freeze, rinse repeat. If you average that out, you might see only a small rise in winter temps, or a normal total amount of snowfall, but that is not how it's experienced by either plants or by people. Constant freeze-thaw cycles are really bad for plants which are adapted to spending four to six months in dormancy, and we're just not consistently getting the snowpack that used to buffer the extreme cold snaps. A milder winter overall doesn't necessarily translate to more survivability.

Unfortunately, the article puts that kind of caveat in a very missable slideshow at the end of the article, while in the main text we are told that the hardiness zone "is really one of the best predictors of winter survival and plant survival in general in the landscape", quoting a USDA horticulturalist who worked on the new zone map. The rest of the article does a great job explaining the factors that the USDA zone doesn't consider, so de-emphasizing the other quotes feels like a weird choice.

In general I would love to see a move away from the hardiness zones into a more holistic approach like ecoregions, which can be as broad or as granular as appropriate, but it's going to take a lot of work to get there, and there's currently no incentive for garden media to change their approach. (In fact, there's a perverse incentive, since new and inexperienced gardeners usually blame themselves for plant failure and turn to media sources for help.)
posted by radiogreentea at 11:41 AM on May 14 [2 favorites]

Maybe I'm naive but I'd think if you're buying plants in person then any perennial that isn't being sold as a houseplant ought to be able to make it through the winter. The zones are useful for when you're ordering stuff online though.
posted by any portmanteau in a storm at 12:45 PM on May 14

Maybe I'm naive but I'd think if you're buying plants in person then any perennial that isn't being sold as a houseplant ought to be able to make it through the winter. The zones are useful for when you're ordering stuff online though.

For the most part, garden plants are BIG PLANT, bought in huge quantities, and the differences in garden stores are very minor between states. You might think that like 20% would be the same, 80% more local, even in your local-chain larger nurseries, but it's more like 80% are the same and 20% local. So you have to shop at the boutique, higher priced nurseries for a more local selection, or online.
posted by The_Vegetables at 3:03 PM on May 14 [1 favorite]

I wonder if this is a difference between how garden centres in Canada and the US operate, or, because I'm in the most populated part of Canada, the plants here are that default 80% that get sent to all the other provinces even if they aren't particularly suited to the climate there.
posted by any portmanteau in a storm at 4:29 PM on May 14

Last winter didn't have a really hard freeze, so this spring we have ticks like I've never seen.
posted by acrasis at 5:06 PM on May 14

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