USDA Hardiness Zones Explained
Your hardiness zone is the single most useful number in gardening. It tells you what plants survive your winters and shapes every planting date in your garden calendar.
What is a hardiness zone?
The USDA Plant Hardiness Zone Map divides North America into 13 zones based on the average annual extreme minimum winter temperature — the coldest it typically gets in a given location. Zones are divided into “a” and “b” sub-zones (5°F increments).
For raised-bed vegetable gardeners, the zone primarily tells you two things: your typical last spring frost date and your typical first fall frost date. These two dates define your growing season length, which determines what you can grow from seed outdoors and when to start transplants indoors.
Find your zone
The fastest way: enter your ZIP code in the JoeBees planner — it looks up your zone automatically and uses it to filter the plant palette and surface frost warnings.
You can also search the official USDA 2023 hardiness zone map by ZIP code for full sub-zone resolution.
Zones at a glance
Frost dates are averages — your microclimate, elevation, and urban heat island can shift them by 1–3 weeks. Always confirm with a local extension service for critical plantings.
| Zone | Climate | Avg winter low | Last spring frost | First fall frost | Season | Good for… |
|---|---|---|---|---|---|---|
| 3–4 | Very Cold | −40 to −20 °F | May 15 | Sep 15 | ~120 days | Kale, radish, peas, chives, garlic, onion |
| 5 | Cold | −20 to −10 °F | Apr 30 | Oct 5 | ~155 days | Tomatoes (short-season), lettuce, carrots, beans, beets, broccoli |
| 6 | Cool–Moderate | −10 to 0 °F | Apr 15 | Oct 15 | ~180 days | Tomatoes, peppers, cucumbers, squash, all cool-season crops |
| 7 | Moderate | 0 to 10 °F | Apr 1 | Nov 1 | ~215 days | Most vegetables and herbs; 2 seasons of cool crops |
| 8 | Warm | 10 to 20 °F | Mar 15 | Nov 15 | ~245 days | Year-round cool crops; long tomato/pepper season |
| 9 | Hot | 20 to 30 °F | Feb 15 | Dec 1 | ~290 days | Two tomato seasons, subtropical herbs, sweet potatoes |
| 10+ | Subtropical/Tropical | 30 °F+ | Jan 31* | Dec 15* | ~320+ days | Year-round growing; tomatoes in winter, cool crops in summer |
* Zone 10+ frost dates are approximate; many areas are frost-free year-round.
Zones vs. heat zones
The USDA hardiness zone measures cold tolerance. A separate system — the AHS Plant Heat Zone Map — measures summer heat stress (number of days above 86 °F). For most vegetables this matters less than the frost dates, but heat-sensitive crops like lettuce and spinach bolt faster in high-heat-zone gardens.
Microclimates and raised beds
Raised beds warm up 2–4 weeks earlier in spring than in-ground beds because the soil mass is surrounded by air on multiple sides. This effectively extends your growing season by roughly half a zone at the start of the year. A frost cloth or cold frame adds another 2–4 weeks on either end.
- South-facing walls and fences reflect heat — effectively warmer than your zone.
- Low-lying areas collect cold air overnight — effectively colder.
- Urban areas run 2–5 °F warmer than surrounding rural areas (urban heat island).
Plan a bed optimized for your zone
Enter your ZIP code in the planner and JoeBees automatically uses your zone to filter plants, surface frost warnings, and generate AI layouts timed to your climate.
Open the Planner →