Beginner guide
Understanding USDA plant hardiness zones
The USDA Plant Hardiness Zone Map is the standard way US gardeners decide which perennials, shrubs and trees will survive their winters. It is based on one number: how cold your area typically gets in winter.
Updated 26 Oct 2026 · Facts checked against the sources at the end.
What a hardiness zone means
Each zone is based on the average annual extreme minimum winter temperature: the coldest temperature of the year, averaged over 30 years. The 2023 USDA map uses weather data from 1991 to 2020.
Each zone covers a 10°F range, and each zone is split into two half zones, 'a' and 'b', 5°F apart. Zone 6a is colder than zone 6b. The full map runs from zone 1 to zone 13; zones 12 and 13 appear only in Hawaii and Puerto Rico.
How to find your zone
The official USDA ARS website has an interactive map: type in your ZIP code and it shows your half zone. Our zone tool lets you pick your zone and see which plants on this site can stay outdoors year-round there.
What changed with the 2023 map
The USDA released the updated map in November 2023. It used data from many more weather stations than the 2012 map (13,412 compared with 7,983). About half of the country shifted into the next warmer half zone, and the other half stayed the same. USDA noted that many shifts reflect better mapping and normal year-to-year swings, not only a changing climate.
How to use zones when you shop
- Plant tags list a zone range, such as 'zones 5 to 9'. If your zone is in the range, the plant should survive a typical winter where you live.
- Zones matter for perennials, shrubs, trees and bulbs. Annuals like zinnias and summer crops like tomatoes live for one season, so zones do not limit them.
- Houseplants such as snake plant list warm zones (often 10 and up) because they cannot take frost outdoors.
- Some plants also have an upper limit: tulips, lilacs and peonies need winter cold to flower well.
What zones do not tell you
A zone is only about winter cold. It does not tell you about summer heat, humidity, rainfall, soil or your first and last frost dates. Two places in the same zone can be very different to garden in. Local conditions matter too: a sheltered wall can be warmer than an open hilltop nearby.
For planting dates, use your average last spring frost date, which you can get from your local extension office. Our planting calendar uses that date.
USDA zone temperature ranges
Average annual extreme minimum temperature for each half zone (USDA 2023 map).
| Half zone | Range | Half zone | Range |
|---|---|---|---|
| 1a | -60 to -55°F | 1b | -55 to -50°F |
| 2a | -50 to -45°F | 2b | -45 to -40°F |
| 3a | -40 to -35°F | 3b | -35 to -30°F |
| 4a | -30 to -25°F | 4b | -25 to -20°F |
| 5a | -20 to -15°F | 5b | -15 to -10°F |
| 6a | -10 to -5°F | 6b | -5 to 0°F |
| 7a | 0 to 5°F | 7b | 5 to 10°F |
| 8a | 10 to 15°F | 8b | 15 to 20°F |
| 9a | 20 to 25°F | 9b | 25 to 30°F |
| 10a | 30 to 35°F | 10b | 35 to 40°F |
| 11a | 40 to 45°F | 11b | 45 to 50°F |
| 12a | 50 to 55°F | 12b | 55 to 60°F |
| 13a | 60 to 65°F | 13b | 65 to 70°F |
Frequently asked questions
What is my USDA hardiness zone?
Enter your ZIP code on the official USDA ARS Plant Hardiness Zone Map website. It shows your half zone, such as 7a.
What does 'a' and 'b' mean in a zone?
Each 10°F zone is split into two 5°F half zones. The 'a' half is the colder one.
Did the hardiness zones change in 2023?
Yes. The 2023 map used newer data (1991 to 2020) and more weather stations. About half of the country moved into the next warmer half zone.
Do hardiness zones matter for annuals?
Not really. Annuals live for one season. Zones matter for plants that must survive winter outdoors: perennials, shrubs, trees and bulbs.
Sources
- USDA ARS: 2023 Plant Hardiness Zone Map
- USDA ARS: How to Use the Plant Hardiness Zone Maps
- USDA ARS: USDA Unveils Updated Plant Hardiness Zone Map (2023)
Written in our own words from the sources above. See our editorial policy. Spotted a mistake? Tell us.