by Connie Oswald Stofko
What plants will last through the winter in your garden? You can figure that out by knowing what hardiness zone you are in. And you may be in a warmer zone than you thought.
A new version of the Plant Hardiness Zone Map was released last week by the United States Department of Agriculture (USDA).
The map is based on the average annual minimum winter temperature. The zones go from coldest to warmest; 5 is colder than 6. Each zone is also divided into “a” and “b.”
In this new map, Western New York looks different than it did on the previous map, which was released in 2012. Many WNY gardeners will notice their landscape has shifted to the next warmer half zone. Other gardeners remained in the same half zone.
Take a look at the image above. Notice that most of the purple area that we saw in 2012 is almost gone. That area was Zone 5a and is now colored in blue to designate it as 5b, which is warmer than 5a. You’ll also see that some areas that were in Zone 5b (blue) are now in Zone 6a (dark green) and some areas that were in Zone 6a (dark green) are now in Zone 6b (light green). (The orange lines are roads.)
Zone 5a, which is almost gone in Western New York, has average low temperatures from -20 to -15 degrees Fahrenheit. The warmest zone here is Zone 6b, which has average low temperatures from -5 to 0 degrees Fahrenheit.
UPDATE: A reader notes that there is a narrow area along Lake Ontario that is 7a, which is warmer than 6b. If you go to the new map and zoom in, you can see it.
The designations don’t reflect the coldest it has ever been or ever will be at a specific location, according to the USDA. The designations on the new map are the average lowest winter temperature for the location from 1991 to 2020.
The practical application of the zones is in choosing plants. If you see a plant tagged as Zone 6, and you live in Zone 6, the plant should make it through the winter. However, if you live in the colder Zone 5, it’s less likely that plant will survive the winter.
On the other hand, if you live in the warmer Zone 6 and see a plant labeled for the colder Zone 5, that plant should have no trouble making it through your milder winter.
To find out what zone you live in, look at the new map here.
There is also useful information on the How to Use the Maps, especially in Section 4: Background for Map and its Use. For example, if you are in a new half zone, you don’t need to change what you are growing. What has thrived in your yard will most likely continue to thrive. There is also information on microclimates.
The new map is more accurate and contains greater detail than prior versions, according to the USDA. It was jointly developed by USDA’s Agricultural Research Service (ARS) and Oregon State University’s (OSU) PRISM Climate Group.
If you want to see what zone you were in previously, see the 2012 map here.