USDA Hardiness Zones Explained
A hardiness zone tells you how cold your winters get, and so which perennials, shrubs and trees can survive them.
What a hardiness zone is
The USDA Plant Hardiness Zone Map divides North America into 13 zones according to the average lowest winter temperature of each area. Each zone covers a band of 10°F. Zone 1 is the coldest, with lows below −50°F (−46°C). Zone 13 is the warmest, with lows above 60°F (16°C).
Each zone is split into two halves of 5°F, labeled a and b. Zone 6a, for example, has average winter lows of −10 to −5°F, and zone 6b has lows of −5 to 0°F.
A plant listed as "hardy in zones 5 to 8" should survive winter where lows fall as far as −20°F (zone 5), and it also performs well in the heat and mild winters of areas up to zone 8.
Find your zone
If you live in the United States, enter your ZIP code on the official USDA map website. Anywhere else, look up the lowest temperature of an average winter and use our hardiness zone finder, which converts that temperature into a zone.
Zone temperature chart
| Zone | Average lowest winter temperature |
|---|---|
| 3 | −40 to −30°F (−40 to −34°C) |
| 4 | −30 to −20°F (−34 to −29°C) |
| 5 | −20 to −10°F (−29 to −23°C) |
| 6 | −10 to 0°F (−23 to −18°C) |
| 7 | 0 to 10°F (−18 to −12°C) |
| 8 | 10 to 20°F (−12 to −7°C) |
| 9 | 20 to 30°F (−7 to −1°C) |
| 10 | 30 to 40°F (−1 to 4°C) |
| 11 | 40 to 50°F (4 to 10°C) |
What zones do not tell you
A zone describes winter cold and nothing else. Two places in the same zone can have very different growing conditions. Zones do not account for:
- Summer heat. Peonies and tulips need winter chill and struggle in warm zones even though they would survive the winter.
- Rainfall and humidity. Lavender is hardy in zone 5 but dies in wet winter soil.
- Snow cover, which insulates roots.
- Frost dates. Your last spring frost and first fall frost decide when to sow annuals and vegetables.
Microclimates
Your garden has warmer and colder pockets. A bed against a south-facing wall can behave like the next warmer zone. A low spot where cold air settles, or an exposed, windy corner, can behave like the next colder one. Use sheltered positions for plants at the edge of their range.
Zones for annuals and houseplants
Annuals complete their life in one season, so zones matter little for them. Plant them after your last frost. Houseplants are mostly tropical plants from zones 10 to 12. They can spend summer outdoors and must come inside before nights fall below about 50°F (10°C).