What are your thoughts on the new USDA hardiness zone changes?

I am in zone 9a, Florida panhandle, my zone did not change since the new update but I really think my zone is 8b (which would be what the old 1990 (?) USDA hardiness zone classified the panhandle. anyways I’ve been here for 7 years and we have gone to the upper teens every winter I’ve been here, so I really think I am in zone 8b. also, I’ve been monitoring the temps very closely this winter on my thermometers and I am always getting colder readings at night compared to what multiple weather stations report, it could be that I am in a less populated part of town so it’s colder but I also look at weather underground’s map to see the nearby weather stations near me and I see wide variations in temperatures for my area, sometimes by 10 degrees, so there are definitely warmer pockets of town.


I’m hoping the USDA will adopt the Sunset Climate Zone methodology.


What Richard is inferring is that climate “zones” are a very poor method of rating an areas variation in climate. I concur, however, we are still stuck with zones for the near future. As for your personal microclimate, that is entirely subjective and likely varies quite a bit from areas just a few miles away.

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… “USDA cold hardiness zones” don’t hold a candle to “Sunset Climate Zones”.


As fellow west coaster I agree with you on this. Nurseries even try to use zones to communicate heat which is utter bullshit when I live in a “zone 8” that can barely grow corn

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I do agree (Sunset Zone 5 here!), but I have only seen them for the west coast. Is that why they are called sunset zones, i.e., the sun sets in the west? I think there would need to be hundreds of sunset zones to really expand the idea effectively across North America, and thousands of them for the entire world. It’s a great local/regional tool, but doesn’t generalize globally as well as something ridiculously simple like the USDA hardiness zones.

If you tried to simplify the sunset zone concept enough to make it possible to generalize globally, I think you might end up with something more like the Köppen classification system (Csb here!), but that really isn’t geared toward temperature extremes as much as the overall pattern of temperatures and precipitation. Plants that flourish in some parts of Köppen Csb will completely fail here, and vice versa. But the same is true for USDA zones, and I’d say that problem is worse for the latter.

In the end, I think all three systems tell you important information, but nothing else beats the USDA hardiness zones when it comes to the ease of calculating it for anywhere on the planet that has a history of temperature data. And it’s a simple concept that uses a linear scale, making it easy for almost anyone to learn how to use.

For example, it’s not at all intuitive that if I wanted to “zone push” here in sunset zone 5, I should probably look at things that do well in sunset zones 15/16/17, the slightly warmer versions of a my zone, rather than looking at things that do well in zones 6,7,8, etc.

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My memory says it was because the publication originally responsible for their publication and probably creation was Sunset Magazine which was all about the West. Of course, my memory cannot automatically be trusted, but I started my long life time relationship with plants, weather and soil in S. CA. .

jamie, I think a wide range of temps within small areas is pretty common but it’s interesting that you get such a wide range of fluctuation where the topography is so flat. I wouldn’t think a small town would create such a range based on roads and buildings. However, I’ve never seen this subject discussed beyond how weather is affected in big cities like NYC.

Here’s what Chatai has to say about it.


Do small towns tend to have markedly warmer temps than nearby less developed areas due to buildings and roads?



Yes, small towns can indeed experience slightly warmer temperatures compared to nearby less developed areas due to what’s known as the urban heat island (UHI) effect. This effect occurs when urban or developed areas experience higher temperatures than their rural surroundings due to human activities and modifications to the landscape.

Several factors contribute to the UHI effect in small towns:

  1. Buildings and Roads: The materials used in buildings and roads, such as concrete and asphalt, absorb and retain heat, causing them to release it slowly over time. This process can lead to higher nighttime temperatures in urban areas compared to rural areas where the land is more exposed and able to release heat more efficiently.
  2. Reduced Vegetation: Urban areas typically have less vegetation compared to rural areas, which leads to reduced evapotranspiration (the process by which water is transferred from the land to the atmosphere by evaporation from the soil and transpiration from plants). This reduction in vegetation can result in less cooling through evaporation and transpiration, contributing to higher temperatures.
  3. Human Activity: Human activities such as transportation, industrial processes, and energy consumption generate heat, further elevating temperatures in urban areas.
  4. Albedo Effect: Urban surfaces often have lower albedo, meaning they absorb more sunlight and reflect less compared to natural surfaces like forests or fields. This absorption of solar radiation contributes to higher temperatures in urban areas.

While small towns may not experience as pronounced of a UHI effect as larger cities, they can still observe localized warming due to these factors, especially when compared to nearby rural or less developed areas. However, the magnitude of this effect can vary depending on factors such as town size, location, and surrounding land use patterns.

It appears that sunset magazine used to have a sunset zone map for all of the USA, yet appears to be gone now https://discover.hubpages.com/living/zone5


I have two gardens 35 miles apart. Day and night difference as one is near a large river in the Great Lakes system.
The marine environment is everything in both my gardens. The closet garden to the water has high humidity, high winds, and higher pest pressure.
The garden farther from the water still benefits from the buffering of the temperatures making seasonal transition smooth and consistent. Less humidity, less wind, less pest pressure.
It’s almost ideal as plants grow big and are healthier. Only 35 miles apart.
So I struggle to keep plants alive in one and need sharp tools to keep down the growth in the other.
Close enough to be the same zone (6).


I try to look up "sunset chill " zones and only music videos pop up.

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I found a site that still has all 45 sunset zones for the contiguous 48 states (and a bit of Mexico and Canada), and I think that confirms my suspicion that it would take hundreds of such zones to cover every climate zone on the planet effectively (and it seems like they already are using zone 1 as a bit too much of a catch-all for a range of cold climates):

I think one salient point is that there isn’t necessarily all that much wrong with the USDA zones. Maybe they could add a bit of information about dispersion so that people would know if they’re in a zone 7a that sometimes gets “zone 5b winters” or if they only sometimes get “zone 6b winters.” It would be messy, of course, mine would probably look like 8a(6b,9a). The other thing is hours at the minimum, but that’s basically impossible to convert to a simple number. Those are the only quibbles I have with the USDA zones.

But boy do I have quibbles and quills and kibble to make of how folks who aren’t the USDA use those zones.

I think USDA zones work better for the continental climates of the eastern U.S. than for the maritime or mediterranean climates of the west. Our winter lows here are usually either in the 9a or 8b range, for example, but our highs are never above the 50s in winter and rarely above the 40s, and our summers lack the heat that many plants want that flourish in zones 8/9 (east coast). It’s that kind of nuance that the sunset zones capture better.


Right, but isn’t warmth a misuse of USDA hardiness zones? I’ll grant that a lot of plants need warm summers for proper winter hardiness, but still, USDA zones are just about average lows, they shouldn’t be used for other purposes like seasonal heat units.

i’m in Navarre, and most of the coastal panhandle is flat topography, no dramatic changes in elevation until you really go towards Alabama and Georgia, so most likely it’s all the forests and fields near me and being in the interior of a peninsula that’s why it’s colder, but i also noticed with the new updates that some parts of neighboring towns west and east of me like Gulf Breeze and Destin are considered 9b. i really think that is a far stretch considering the winter lows we have here. only if you live very close to the water, like you can see the Gulf of Mexico from your house, do you experience warmer temps. here’s a map of my area with nearby weather stations. i had 33 degrees on my thermometers that morning at that time.


If someone made a seasonal heat unit map and made the zone names match the hardiness zones in the east, that would allow reinterpretation of things like “this plant is can be grown in zones 5 to 8”

I still think the problem is people saying stuff like “can be grown in zones 5 to 8.” They should be saying stuff like “hardy to zone 5, can be grown in heat regions 6 to 9.” Minimum winters lows and summer heat units is an at least four dimensional space, there’s no way to practically map that to one dimensional zone numbers. Even just mapping minimum winter lows to zone numbers is messy and problematic.

For example, USDA zones, like I mentioned earlier, don’t tell you dispersion, which is a big deal because some parts of zone 8 can get -5 F winters, and some parts of zone 8 never see anything worse than 10 F. But it’s actually worse than that, because the distribution is lop-sided. My zone 8a can have all the way down to zone 6b temps, but I’ve never had a zone 9b winter, not even close. So just accurately talking about average winter minimums you need to use three different numbers.

Looking at it from the other side, USDA zones don’t capture nuances in chill hour accumulation either. Both Napa, where I live, and Jacksonville, Florida are in zone 9b, but while I get an average of 1000 chill hours every winter, Jacksonville gets somewhere around 5-600. I can grow cold-climate things like herbaceous peonies and sweet cherries with no problem. In fact, some good bulb nurseries have caught on and will have separate zone ratings for the east and west coast, with many bulbs being rated a good zone “warmer” for the west coast, e.g. this catalog description of a tulip from Old House Gardens:

Now all but extinct, this sturdy little rose and white tulip was a popular American sweetheart for many, many years. New York City’s J.M. Thorburn offered it as early as 1872, and it continued to be widely catalogued well into the 1930s, a reflection of its charm and excellence. Thanks to the Hortus Bulborum for saving it! Single Early, 10”, zones 4b-7b(8bWC), from the Hortus.

Conversely, subtropical and tropical things like plumerias, mangos, and pineapples that need protection only in the coldest winters in Florida are much more difficult to grow here, despite winter lows being generally comparable. The difference being that we will be in a range of 35-55 degrees and rainy for weeks at a time, and summer night time temps are often in the 50’s.


It’s not really a misuse so much as a shortcoming, because the whole point of that system is to answer “what can I grow here?”

So if I see a list of plants that do well in sunset zone 5, I can be pretty confident they will do well here without needing to research much else about the needs of the plant, because sunset zones capture lows, highs, and precipitation.

Here are some backyard observations affected by microclimate.

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