You may have run into the term “hardiness zone” when looking at a packet of seeds, the label on a plant at your local garden shop or when looking up plant and flower information online. But what are hardiness zones? In this article we will explain what hardiness zones are, how to use them, and look at the planting hardiness zones by state.
What is a planting hardiness zone?
Planting hardiness zones were created by the United States Department of Agriculture. They are meant to be used as a guide for knowing what plants will survive in a given geographic area, based on that areas extreme minimum temperature.
The current version of the hardiness zone map was updated in 2012, and uses weather data collected from 1976 to 2005. The data looked at is an areas lowest annual temperature, or the extreme minimum. These extreme minimum temperatures were recorded each year over a 29 year period to create an average for each location. The lowest and highest ends of the average minimum temperatures calculated run from -60°F to 70°F. This range was split up into 13 “zones”, each zone covering a 10 degree Fahrenheit range.
For example, zone 1 starts with extreme minimum temperatures between -60°F and -50°F, and continues in increments of 10 degrees until finishing at zone 13 who’s extreme minimum temperature is 60°F to 70°F. Each zone is sometimes further broken down into an “a” and a “b”, which narrows the increments down to 5°F.
So when you see a plant labeled with one or more hardiness zone numbers, that information will tell you which zones that plant is most likely to grow well in, and can survive that region’s typical low temperatures.
USDA planting zones by state
| State Name | Hardiness Zones |
|---|---|
| Alabama | 7a - 9a |
| Alaska | 1a - 8b |
| Arizona | 4b - 10b |
| Arkansas | 6b - 8a |
| California | 5a - 11a |
| Colorado | 3a - 7a |
| Connecticut | 5b - 7a |
| Delaware | 7a - 7b |
| Florida | 8a - 11b |
| Georgia | 6a - 9a |
| Hawaii | 9a - 13a |
| Idaho | 3b - 7b |
| Illinois | 5a - 6b |
| Indiana | 5b - 6b |
| Iowa | 4b - 6a |
| Kansas | 5b - 7a |
| Kentucky | 6a - 7a |
| Louisiana | 8a - 10a |
| Maine | 3b - 6a |
| Maryland | 5b - 8a |
| Massachusetts | 5a - 7b |
| Michigan | 4a - 6b |
| Minnesota | 3a - 5a |
| Mississippi | 7b - 9a |
| Missouri | 5b - 7b |
| Montana | 3a - 6a |
| Nebraska | 4a - 5b |
| Nevada | 4a - 10a |
| New Hampshire | 3b - 6a |
| New Jersey | 6a - 9a |
| New Mexico | 4b - 9a |
| New York | 3b - 7b |
| North Carolina | 5b - 8b |
| North Dakota | 3a - 4b |
| Ohio | 5b - 6b |
| Oklahoma | 6a - 8a |
| Oregon | 4b - 9b |
| Pennsylvania | 5a - 7b |
| Rhode Island | 6a - 7a |
| South Carolina | 7a - 9a |
| South Dakota | 3b - 5b |
| Tennessee | 5b - 8a |
| Texas | 6b - 10a |
| Utah | 4a - 9a |
| Vermont | 3b - 5b |
| Virginia | 5a - 8a |
| Washington | 4a - 9a |
| West Virginia | 5a - 7a |
| Wisconsin | 3b - 5b |
| Wyoming | 3a - 6a |
Alabama
Located in the heart of the south, Alabama’s hardiness zones range from 7a in the north to 9a in the far southern areas of Mobile and Dothan. In southern Alabama some tropical plants like palm trees can survive. You can see the planting calendar for Alabama on the Farmer’s Almanac.
Alaska
In far northern Alaska you have zones 1a through 2b. Middle Alaska is a mix of zones 1b through 3a. Southern Alaska is mainly 2b through 3b, with 4b right along the southern coast. The Alaska peninsula and coastal areas along the Gulf of Alaska add in zones 6a – 7a, and pockets of 7b – 8b can be found around Sitka and Ketchikan. The Aleutian Islands also tend towards a warmer climate with zones 6 – 8.
Fort Yukon, at zone 1a, is the coldest hardiness zone in the United States.
Arizona
Northeastern Arizona mainly ranges between 6a – 8a with pockets of 4b – 5b around Flagstaff and Baldy Peak. Things warm up in the southeastern portion of the state starting around Phoenix, with zones ranging from 8a to 10a with small pockets of 10b.
Arkansas
Zone 6b can be found along much of the northern Arkansas boarder, followed by 7a, then 7b. Most of the southern half of the state, starting around Little Rock, is zone 8a. Here is the planting calendar from the Farmer’s Almanac for Arkansas.
California
Perhaps unsurprisingly due to its immense size, California has the widest range of hardiness zones of any state. The northern half of California ranges from 5a to 10b. Zones 5 and 6 are found on the eastern side of the Sierra Nevadas, where zone 10 is mainly around San Fransisco and San Jose.
Southern California has a wide range also, from 5a to 11a. The northeastern corner contains most of the lower zones while zone 11a can be found around Los Angeles and the far southeastern corner of the state.
Colorado
The Rocky Mountains provide some high elevations in Colorado and therefore some lower hardiness zones. Zones 3-5 are found throughout most of the Rockies, where lower elevations on either side mainly contain zones 5b – 7a.
Connecticut
Connecticut has a relatively small hardiness zone range, from 5b to 7a. Zone 5b is only found in the northwest corner of Litchfield county. The majority of the state is zone 6, and zone 7a is found along the coast.
Delaware
Delaware only has one hardiness zone, zone 7. The majority of the state is 7a, while the coastal area east of Georgetown is 7b. Check out some ideas on zone 7 plants here.
Florida
The warm and sunny state of Florida contains zones 8 through 11. The Panhandle and northern border are zone 8. Jacksonville, Gainesville and Ocala are zone 9a. Middle Florida from Orlando to Fort Myers is zone 9b, and southern Floria fills in zones 10 and 11, with the Florida Keys reaching zone 11b.
Georgia
Georgia has a pretty consistent gradient of hardiness zones from north to south. North of Atlanta, you have zones 6a – 7b. The middle of the state from Atlanta to south of Macon is zone 8a, and the southern part of the state is 8b. There is a small swath of 9a along the southeastern coast.
Hawaii
It’s probably no surprise that the tropical Hawaii has the warmest hardiness zones of any state, ranging from 9 all the way to 13a. Only the high volcanic peaks of the Big Island, Maui and Kauai have areas below zone 11.
Idaho
Idaho has a mix of hardiness zones from 3 to 7. Zones 3b to 5b can be found in the eastern part of the state. Warmer zones 6 and 7 can be found in the south western section of Idaho as well as the northern tip from Grangeville to Sandpoint.
Illinois
Illinois is pretty evenly divided right in the middle between zones 5 and 6-7. From Springfield north, Illinois is mainly zone 5b with a small section of 5a in the far northwest corner. South of Springfield to Mount Vernon is zone 6a, and beyond Mount Vernon zone 6b. The very southern tip of Illinois switches to zone 7a. Find out the planting schedule for your town here.
Indiana
Indianapolis acts as the dividing line of the two main hardiness zones in Indiana, 5b and 6a. Zone 5b is mainly found in the northern half of the state, and 6a in the southern half. The far southern tip of Indiana around Evansville and extending to Jeffersonville moves up to zone 6b.
Iowa
The Hawkeye state is pretty solidly zone 5, with some exceptions. The bulk of Iowa is zone 5a, with the southern border and southwestern corner being 5b. Check out this page for ideas of plants hardy in zone 5. Up along the northern border, the eastern and western corners shift to 4b, whereas the far southern tip of Lee county dips its toe into zone 6a.
Kansas
The counties along the northern border of Kansas are mainly zone 5b. Across the middle of the state you have zone 6a, and roughly south of Hutchinson things switch over to 6b. There are a few small pockets in Harper and Sumner counties make it up to zone 7a.
Kentucky
Kentucky does not have a large range of hardiness zones. In fact, the vast majority of the state is zone 6b with some 6a mixed in. The far southwestern tip, and the western half of the southern border, creep into zone 7a.
Louisiana
Louisiana, as a whole, is solidly a zone 8 and 9 state. In the far north you start with zone 8a, then the large middle section of the state is zone 8b. South of Baton Rouge you move into zone 9a, with small sections of zone 9b around New Orleans and the far southeastern tip. Interestingly, the USDA has marked off a very small section of Venice Louisiana as zone 10a.
Maine
The northern half of Maine, including most of the state that juts into Canada, is a mix of zone 3b and 4a. The southern half of Maine, starting around Penobscot switches zones in thin east-west strips starting at zone 4b and ending with 5b along the coast. There are also some small sections of zone 6a found on the coast and islands between Brunswick and Bar Harbor.
Maryland
The far western handle of the state that stretches into the Appalachian Mountains is where you will find zones 5b and 6a. Much of the northern border is zone 6b, and the rest of the state is zone 7, with 7b being the coastal areas. There is a small pocket of 8a at the far southern tip, on the eastern side of the Chesapeake Bay.
Massachusetts
Massachusetts is divided into the cooler zone 5 in the western half of the state and the slightly warmer zone 6 in the eastern half of the state. Cape Cod, Martha’s Vineyard, Nantucket and the coastal area of Boston fall into zone 7.
Michigan
Michigan’s upper peninsula tends to have cooler minimum temperatures, and therefore some colder hardiness zones. Zones range from 4a through 5b. The cooler hardiness zones of 4a through 5a can also be found in the northern lower peninsula. Central and southern areas of the lower peninsula trend a bit warmer with zones 5b through 6b.
Minnesota
Minnesota is pretty evenly divided between zones 3 and 4. The northern half of the state is mainly zones 3a and 3b. A small belt across the middle of the state is zone 4a, while most of the southern half of the state is 4b.
Mississippi
The state of Mississippi contains three hardiness zones, 7 through 9. The northern section, containing Oxford and Tupelo, is zone 7b. The large middle section of the state and the northwest border is mainly zone 8a. The southern counties are zone 8b, with a small strip along the coast of the Gulf of Mexico moving into zone 9a.
Missouri
Northern Missouri is zone 5b, and the large middle section of the state is zone 6a. Most of southern Missouri is 6b, with the far southeastern corner moving into zone 7a and 7b.
Montana
The northern state of Montana has a mix of hardiness zones from 3 to 6. Much of northern and eastern Montana ranges from 3a to 4a, and transitions into 4b – 5b in the west. A small area of zone 6a can be found in the far northwestern corner.
Nebraska
Nebraska is a fairly uniform state, with the majority of the state falling into zone 5. The southern section of Nebraska is zone 5b, while the middle and northern sections are 5a. Check here for a nice list of zone 5 plants. There are also patches of zone 4b in the northwestern portion of the state. Interestingly, the USDA makes a distinction for a small section of land around the Oglala National Grassland as being zone 4a.
Nevada
Many people think of Nevada as simply being “hot” because of the desert climate of Las Vegas. However, Nevada has quite a range of hardiness zones from 4 to 10. The mountainous region in the northeastern section of the state is responsible for some of the cooler zones of 4a through 6a. West of Austin, the hardiness zones climb to 6a through 8a. The warmest zones in Nevada are found in the southern tip, which climb to zones 8, 9 and 10.
New Hampshire
New Hampshire has a gradient of hardiness zones from north to south. Zones 3b through 4b can be found in the northern section of the state, beginning around Grafton. A small middle section of 5a transitions into 5b for most of the southern portion of the state starting around Laconia. A few sections in southern New Hampshire make it into zone 6a.
New Jersey
New Jersey has a short range of hardiness zones that only consist of zone 6 and zone 7. The coolest zone, 6a, is found in the upper northwestern corner around Sussex county. Meanwhile the warmest zone, 7b, can be found around Cape May and Atlantic City in the east and Gloucester county in the west. The rest of the state falls within zones 6b-7a.
New Mexico
The majority of New Mexico falls into hardiness zones 6a through 7b. The southwestern corner from Alamogordo to Hidalgo county has the warmest zones ranging from 8a to 9a. Some cooler zones are present in the state too, with pockets of zones 4a to 5b along the northern border and west of Albuquerque.
New York
New York has many hardiness zones that range from 3 to 7. The coolest zones are found in upstate New York, north of Utica. In this section of the state zones range from 3b to 5a. The middle section of the state mainly stay within zones 5a and 5b. The western border of the state up until Oswego falls within zone 6. The southern tip of the state, including Long Island, also fall into warmer zones ranging from 6a to 7b.
North Carolina
North Carolina’s hardiness zones run in a gradient from west to east. The far western portion of the state, west of Asheville and Boone, runs cooler with zones between 5b and 7a. The central portion of the state between Raleigh and Asheville stays in zone 7b. East of Raleigh to the coast the zone shifts to 8a with some small pockets of 8b along the Outer Banks.
North Dakota
North Dakota doesn’t have a large range of hardiness zones, with most of the state falling into either zone 3b or 4a. Counties along the northern border are considered zone 3b with small pockets of 3a. South of Lakota and Minot, the rest of North Dakota falls into zone 4a with a few small pockets of 4b. Plants that perform well in zones 3 or 4 should do well anywhere in North Dakota.
Ohio
Ohio is a very uniform state when it comes to hardiness zones. The vast majority of the state is hardiness zone 6. A few pockets of zone 5b exist throughout the state. For some good ideas on hardiness zone 6 plants, check the list here on Gardenia.
Oklahoma
Hardiness zones in Oklahoma range between 6 and 8. In the panhandle and along the northern border is where you can find zones 6a and 6b. Across the middle of the state is zone 7a, which then transitions into zone 7b in the south. The far southeastern tip of the state, in the southern parts of Choctaw, Bryan and McCurtain counties, the zone is considered to be 8a.
Oregon
Oregon has two fairly distinct “cluster” of hardiness zones. The western third of the state is made up of zones 8a – 9b. The eastern two thirds of the state mainly stays within zones 6a – 7b. There are also pockets in this section of cooler zones 4b to 5b.
Pennsylvania
Pennsylvania hardiness zones have a relatively small range, with most of the state falling within zones 5 and 6. Broadly speaking, northern Pennsylvania stays within zone 5b, with small pockets of 5a around Mc Kean and Warren counties. The rest of the state stays within zone 6, with small pockets of zone 7, especially near Philadelphia.
Rhode Island
The small state of Rhode Island exists mainly within hardiness zone 6. In general, the western portion of the state is zone 6a while the eastern portion of 6b. Coastal areas around Westerly and Newport move into zone 7a.
South Carolina
South Carolina largely remains within hardiness zone 8, with the middle portion of the state in zone 8a and the eastern coast area in zone 8b. Along the eastern half of the northern border, many counties fall within zone 7b. Charleston is just warm enough to push it over into zone 9a.
South Dakota
South Dakota find itself squarely in the cooler hardiness zone 4. The majority of the state is in zone 4b, with large swaths of the far northern counties in zone 4a. The southeastern corner, in addition to a few other pockets within the state, slide into zone 5a
Tennessee
Most of the narrow but long state of Tennessee remains in the range of hardiness zones 6b to 7b. Most pockets of zone 6a and 6b are found in the eastern section of the state and along the eastern border. The majority of the rest of the state sits within zone 7a, with the far southwestern corner sliding into zone 7b. A small section south of Memphis is considered to be zone 8a, while the map points out that the area directly adjacent to rivers run a bit cooler in zone 5b.
Texas
Texas is a pretty large state, and that is reflected in the variety of hardiness zones found from north to south. Starting at the top of the west Texas panhandle you have zone 6b and 7a. This transitions to zone 7b as you move towards the middle of west Texas. The middle section from about Midland to Kerrville is zone 8a. South of Kerrville you move into zone 8b and 9a.
In eastern Texas, things end up a little warmer. Starting in the Dallas area you have zone 8a, which moves to 8b around Austin. South of San Antonio transitions into zone 9a, finishing up with zones 9b and 10a at the far southern tip of the state. Check the Farmer’s Almanac here for each town’s planting schedule.
Utah
Utah has hardiness ranges that start at zone 4 and go all the way to zone 9. The higher elevations found in the Uinta Mountains, Bear River Range and Wasatch Range make those areas east of Salt Lake City fall into zones 4a through 5b. The rest of Utah mainly falls within zones 6 and 7, with warmer zones 8 and 9a found along the southern border.
Vermont
The beautiful green mountain state of Vermont mainly stays within zones 4 and 5. The northeastern portion of the state is zone 4a with pockets of 3b around Essex. The rest of the state is a mix of 4b and 5a with small pockets of zone 5b near the southern border.
Virginia
The far western border of Virginia is in zone 6, with tiny pockets of zone 5. East of Charlottesville and Roanoke you’ll find zone 7a, then zone 7b starting at Richmond and moving east. The area around Virginia Beach, Norfolk, and the far eastern portion of the state fall into zone 8a.
Washington
Washington has a range of hardiness zones starting with cooler zones in the east and moving into warmer zones in the west. The northeastern part of the state is where you will find zones 4a through 6a. The central and southern sections of the eastern two-thirds of the state are in zones 6 and 7. In the western third of the state, temperatures transition in zones 8 and 9.
West Virginia
Most of West Virginia remains right within hardiness zone 6. There is a stretch from Pocahontas north to Tucker that dips into hardiness zone 5.
Wisconsin
The hardiness zones in Wisconsin start with the coolest zone in the northwestern corner of the state and move towards the warmest zone along the eastern border. Aside from the coastal area along Lake Superior, the northern section of Wisconsin ranges from zones 3b to 4a. It then transitions to zone 4b along the central portion of the state, into zone 5a from Green Bay down to Madison and the southern border. A think swath of zone 5b extends from Kenosha all the way up the eastern coast.
Wyoming
Unlike some other states where hardiness zones are in very distinct areas, you will see from the map that zones 3a to 5b are heavily mixed throughout the state. Small pockets of zone 6a are sprinkled in the mix, but mainly the state remains between zones 3 and 5.
Final notes
Hardiness zones, while not containing all the information on suitability of a plant for a specific location, can be a great tool. As we mentioned at the beginning of the article, the current version of the hardiness zones map was updated in 2012. The version prior to that was in use since 1990. With climate changes over time, it is likely that sometime in the future the hardiness zones will be updated again, and you may find yourself falling into a new category. It’s worth checking back at usda.gov every so often to keep an eye out for any future updates.
Melanie has a degree in Environmental Science and has always been interested in all things nature from wildlife to plants. In her spare time she enjoys hiking, travel, reading, photography and crochet.