If the plants, shrubs, and trees you bring home seem to struggle every year or don’t make it altogether, they might not be hardy to your growing zone. What’s even more frustrating is that garden centers often sell landscaping plants that aren’t likely to survive winter in your area!
Find out what zone you live in and whether your perennials are matched correctly to your climate below.
Find your USDA zone
Your growing zone tells you one thing
The terms “growing zone,” “USDA zone,” “gardening zone,” and “planting zone” all refer to hardiness ratings from the USDA Plant Hardiness Zone Map (PHZM), which divides North America into 13 growing zones based on their average lowest temperatures in winter.
Each zone is 10°F warmer (or colder) than the next zone, and each zone is further divided into “a” and “b” half zones (in 5° increments) to give a more accurate indication of temperature variations.
Plant hardiness zones help farmers, gardeners, and landscapers determine which perennials are likely to thrive in their climate. The lower the number, the greater the cold tolerance.
For example, a plant that’s hardy to zone 6 can handle a winter low of 0°F to -10°F, while a zone 5 plant is adapted to withstand temperatures of -10°F to -20°F. If we drill down even more, plants in zone 6a should tolerate lows of -5°F to -10°F, while plants in zone 6b should tolerate 0°F to 5°F.
Zones 10 and above include tropical and subtropical climates such as Southern California, South Florida, Hawaii, Puerto Rico, and parts of Texas and Arizona, which rarely or never see a freeze.
Here’s the complete temperature range for each hardiness zone, according to the PHZM:
| Zone | Temp (°F) | Zone | Temp (°F) |
|---|---|---|---|
| 1a | -60 to -55 | 8a | 10 to 15 |
| 1b | -55 to -50 | 8b | 15 to 20 |
| 2a | -50 to -45 | 9a | 20 to 25 |
| 2b | -45 to -40 | 9b | 25 to 30 |
| 3a | -40 to -35 | 10a | 30 to 35 |
| 3b | -35 to -30 | 10b | 35 to 40 |
| 4a | -30 to -25 | 11a | 40 to 45 |
| 4b | -25 to -20 | 11b | 45 to 50 |
| 5a | -20 to -15 | 12a | 50 to 55 |
| 5b | -15 to -10 | 12b | 55 to 60 |
| 6a | -10 to -5 | 13a | 60 to 65 |
| 6b | -5 to 0 | 13b | 65 to 70 |
| 7a | 0 to 5 | ||
| 7b | 5 to 10 |
Your growing zone tells you what will survive winter in your area. Let’s say you want to add some perennial herbs to your garden. You pick up a rosemary and see that it’s hardy to zones 8 and 9. If you live in zone 7, it’s unlikely to make it through a typical winter unless you pot it up and overwinter it indoors. You need to choose a hardier variety (like Arp rosemary) or a hardier herb (like thyme), or treat the rosemary as an annual herb.
When shopping for plants, you might come across labels with a wide range of hardiness zones, such as zones 3 to 8. That means the plant will do well in all those zones, but will struggle in warmer climates. An example would be many popular fall-planted flower bulbs (like daffodils and tulips), which need cold temperatures to stimulate blooming in spring.
That’s really all your growing zone can tell you.
What a growing zone CAN’T tell you
Unfortunately, there’s way more a growing zone cannot tell you when it comes to planting. Your zone can’t tell you…
… How long you might experience extremely cold weather
Your hardiness zone doesn’t really indicate how often or how long you can expect freezing temperatures. Many frost-tolerant plants can withstand brief freezes, especially under frost covers or an insulating layer of snow. However, these same plants will die if freezing temperatures persist for several days or weeks.
Read more: Yes, you can grow vegetables all winter with just a frost cover!
… When it’s time to plant in spring (or fall)
Your growing zone can’t tell you when it’s safe to plant in spring or when the first frost is expected in fall. Even within the same zone, two different cities can have frost dates that are months apart!
Take, for example, Pittsburgh, PA, which falls in zone 6b and has an expected last frost date of April 24. Where I live in Bend, OR (also zone 6b), our last frost isn’t until June 26!
Quick tip
If you’re looking for a reliable chart that tells you when you should sow seeds or set out transplants, use my interactive tool to create a personalized planting calendar, based on your actual frost dates.
… What your microclimate is like
Even though I live in zone 6b, I’m in a much colder microclimate than the rest of Bend (usually 5°F to 10°F colder in winter). I’m also in a dry, high desert region and don’t have the benefit of protective snow cover like colder zones get. Because of that, I consider my “true” zone to be 5, and only buy perennials that are hardy to zones 5 or below.
… What vegetables you can grow
Your hardiness zone can’t tell you the kind of crops that will actually do well in your climate.
Let’s use Portland, OR, and Houston, TX, as examples here (both in zone 9). Gardeners in Portland can grow lettuce through the end of June, when the average highs are around 76°F. (They can even keep lettuce going all summer with a bit of shade and strategic succession planting.) Houston, however, experiences highs of 76°F by April, which means lettuce is best grown through the winter months there.
Related: Try these heat-tolerant lettuce varieties if you live in a warmer zone
What about okra? Zone 9 should be warm enough to grow this heat-loving crop, right? (I had a friend in Houston who once told me they grow two things well: beef and okra!)
And while it’s true that okra thrives in the hot Texan sun, it’s not well adapted to Western Oregon’s cool, cloudy summers and lower night temperatures.
… Whether your plants can survive summer in your area
The USDA Plant Hardiness Zone Map focuses on the average coldest temperatures, but doesn’t say anything about the average hottest temperatures in a given zone.
Take the Portland and Houston example above. Despite both of these cities being in zone 9, they have very different climates, particularly in summer. The average high in Portland in August is 80°F and the low is 58°F. In comparison, Houston’s average high in August is 91°F and the low is 76°F.
Notice how Houston’s low temp is nearly 20° higher than Portland’s low temp? Wild, right?! So a plant that would thrive over the summer in Portland would probably struggle in Houston’s searing heat.
Frequently asked questions
For a more a detailed look at how growing zones can vary in your state, find the corresponding map below. I’ve included 54 USDA hardiness zone maps for the United States and select US districts and territories. You can click on each map to view a larger version on the USDA site.
Alabama
USDA zones 7b through 9b are represented in Alabama.
Alaska
USDA zones 1a through 8b are represented in Alaska.
Arizona
USDA zones 5b through 10a are represented in Arizona.
Arkansas
USDA zones 7a through 8b are represented in Arkansas.
California (North)
USDA zones 5a through 10a are represented in Northern California.
California (South)
USDA zones 5a through 11a are represented in Southern California.
Colorado
USDA zones 3b through 7b are represented in Colorado.
Connecticut
USDA zones 6a through 7b are represented in Connecticut.
Delaware
USDA zones 7a and 8a are represented in Delaware.
District of Columbia
USDA zones 5b through 8a are represented in the District of Columbia.
Florida
USDA zones 8b through 11b are represented in Florida.
Georgia
USDA zones 6a through 9b are represented in Georgia.
Hawaii
USDA zones 8b through 13a are represented in Hawaii.
Idaho
USDA zones 3b through 7b are represented in Idaho.
Illinois
USDA zones 5a through 7b are represented in Illinois.
Indiana
USDA zones 5b through 7a are represented in Indiana.
Iowa
USDA zones 4b through 6a are represented in Iowa.
Kansas
USDA zones 5b through 7a are represented in Kansas.
Kentucky
USDA zones 6b through 7a are represented in Kentucky.
Louisiana
USDA zones 8b through 10b are represented in Louisiana.
Maine
USDA zones 3b through 7a are represented in Maine.
Maryland
USDA zones 5b through 8a are represented in Maryland.
Massachusetts
USDA zones 5a through 7b are represented in Massachusetts.
Michigan
USDA zones 4a through 6b are represented in Michigan.
Minnesota
USDA zones 3a through 5a are represented in Minnesota.
Mississippi
USDA zones 7b through 9b are represented in Mississippi.
Missouri
USDA zones 5b through 8a are represented in Missouri.
Montana
USDA zones 3a through 6b are represented in Montana.
Nebraska
USDA zones 4a through 6a are represented in Nebraska.
Nevada
USDA zones 4a through 10a are represented in Nevada.
New Hampshire
USDA zones 3b through 6b are represented in New Hampshire.
New Jersey
USDA zones 6b through 8a are represented in New Jersey.
New Mexico
USDA zones 5a through 8b are represented in New Mexico.
New York
USDA zones 4a through 7b are represented in New York.
North Carolina
USDA zones 6a through 9a are represented in North Carolina.
North Dakota
USDA zones 3a through 4b are represented in North Dakota.
Ohio
USDA zones 5b through 7a are represented in Ohio.
Oklahoma
USDA zones 6b through 8a are represented in Oklahoma.
Oregon
USDA zones 5a through 10a are represented in Oregon.
Pennsylvania
USDA zones 5b through 8a are represented in Pennsylvania.
Puerto Rico
USDA zones 11b through 13b are represented in Puerto Rico.
Rhode Island
USDA zones 6a through 7b are represented in Rhode Island.
South Carolina
USDA zones 7b through 9b are represented in South Carolina.
South Dakota
USDA zones 4a through 5b are represented in South Dakota.
Tennessee
USDA zones 6a through 8a are represented in Tennessee.
Texas (East)
USDA zones 7b through 10b are represented in East Texas.
Texas (West)
USDA zones 6b through 9b are represented in West Texas.
Utah
USDA zones 4a through 9a are represented in Utah.
Vermont
USDA zones 4a through 6a are represented in Vermont.
Virginia
USDA zones 5b through 8b are represented in Virginia.
Washington
USDA zones 4a through 9b are represented in Washington.
West Virginia
USDA zones 5b through 7a are represented in West Virginia.
Wisconsin
USDA zones 3b through 6a are represented in Wisconsin.
Wyoming
USDA zones 3b through 6a are represented in Wyoming.
