2023 USDA Plant Hardiness Zone Maps Out

[Zone7Bpalmguy]

7 hours ago, Desert DAC said:

Thanks for those links, I'll dig in to them. Something I notice is how many people assume the USDA cold hardiness zones use only weather station data. It also uses PRISM (Oregon State Univ.) climate / terrain modeling, which is good, but it is in no way without some issues. It makes some questionable inferences and assumptions about thermal belts (warm slopes) here in the west that do not line up with reality, let alone extreme cold events where thermal belts and microclimates can really break down - wind advection.

I also don't know if PRISM verifies their initial mapping of zones with various state or local meteorology and horticultural people, but even that can be good and bad - bad when there's a local bias or agenda that some places have.

Here's a great climate zone mapping system for Florida, layering USDA cold hardiness zones over Florida native plant communities:

https://www.fann.org/plant-communities/

That's a very detailed map, I like it. Do they do this for all states or is this just a Florida map done within and for Florida?

[flplantguy]

That map i think is just done for florida, but is off in spots now for the hardiness zones. The plant communities are really good though, and show how the state changes and why some palms do not grow further south that do well north in Central Florida.  That hardiness map is a good major freeze map though, so useful for planning how bad it can get.

[Desert DAC]

On 1/13/2025 at 6:40 AM, Zone7Bpalmguy said:

That's a very detailed map, I like it. Do they do this for all states or is this just a Florida map done within and for Florida?

I plan on adapting something like that for the southwestern states, but will probably start with New Mexico and surrounding states, especially adjacent areas of Texas.

[Cody Salem]

The Oregon State University PRISM group has files of the zones you can download and add as a layer to Google Earth. 

https://prism.oregonstate.edu/projects/plant_hardiness_zones.php

If you have access to ARC GIS software, you can download and view the grid data that was used to make the zone maps.  

It is a raster file that contains the precise temperature assigned to each square kilometer in the U.S.   You will want to select the CONUS Grid data and add it to your basemap, and it should look something like this:

 

 

Of course you can adjust the appearance and contrast a thousand different ways.    Zoom in and you can see each pixel (about 1sq. km), then click them to see the temperature assigned to it.   For some reason its called Stretch.Pixel Value, and they go to six decimal places, but it is just degrees Fahrenheit.

 

 

With this map, I set it to change the shade of color for every 1 deg. F difference.   I've actually found this useful for choosing plants,  if I don't look at the actual number.  For example, if you spot an interesting plant growing in one location, you can calculate pretty close if your location will be a couple degrees warmer or colder.  It even picks up on the areas that can get cold pools and other places that have warm thermal belts above the valleys.   Probably doesn't matter much to you Texans, but on the west coast we can go from a Z9 to a Z6 in less that 50 miles. 

 

 

I though this one was pretty,  I adjusted the contrast so there is only about 15 deg difference between red and blue.