How to Read a USDA Hardiness Zone Map: Complete Guide (2026)
Most gardeners know their zone number. Far fewer know what it actually measures — or what it doesn't. This guide explains exactly what USDA hardiness zones mean, how the 2023 map overhaul changed zones for half the country, and how to use your zone correctly to make smarter plant choices.
Find Your Zone & Planting Dates
Enter your ZIP code to find your exact USDA zone and get personalized planting dates for any vegetable, herb, or fruit.
What a USDA Hardiness Zone Actually Measures
Here's the definition in one sentence: a USDA hardiness zone represents the average annual extreme minimum winter temperature for a location. That's the average of the coldest single night recorded each year, based on 30 years of weather station data.
Notice what it doesn't measure: average winter temperature, snowfall, summer heat, humidity, rainfall, growing season length, or spring frost timing. It measures one thing: how cold does it get on the worst night of a typical year?
The map divides the US into 13 primary zones (Zone 1 through Zone 13), each covering a 10°F range. Each zone is further split into two 5°F half-zones labeled "a" (colder) and "b" (warmer). So Zone 6a covers areas where the coldest night averages −15 to −10°F, and Zone 6b covers −10 to −5°F.
Key principle: The zones exist to answer one question — will a perennial plant survive winter in this location? A lavender plant labeled "hardy to Zone 5" should survive winters where the coldest night averages −20°F or warmer. Plant it in Zone 4 and you're gambling on a milder-than-average winter.
All 25 USDA Hardiness Zones: Temperature Ranges & Locations
Based on the 2023 USDA Plant Hardiness Zone Map using 1991–2020 temperature data. Click a zone to see plant-specific planting dates.
Interior Alaska
Northern Alaska
Fairbanks, AK
Northern Plains
International Falls, MN
Fargo, ND; Duluth, MN
Minneapolis, MN; Burlington, VT
Portland, ME; Bozeman, MT
Chicago, IL; Denver, CO
Columbus, OH; Providence, RI
St. Louis, MO; Louisville, KY
Baltimore, MD; Kansas City, MO
Washington DC; Nashville, TN
Charlotte, NC; Albuquerque, NM
Seattle, WA; Savannah, GA
Portland, OR; Dallas, TX
Sacramento, CA; Phoenix, AZ
Los Angeles, CA; Tampa, FL
Miami, FL; San Diego, CA
South Florida; coastal Hawaii
Hawaii (lower elevations)
Hawaii (Kona coast)
Puerto Rico
Puerto Rico (low elevation)
Puerto Rico (tropical lowlands)
| Zone | Avg Min Winter Temp (°F) | Avg Min Winter Temp (°C) | Example Locations |
|---|---|---|---|
| Zone 1a | Below −60°F | Below −51°C | Interior Alaska |
| Zone 1b | −60 to −55°F | −51 to −48°C | Northern Alaska |
| Zone 2a | −55 to −50°F | −48 to −46°C | Fairbanks, AK |
| Zone 2b | −50 to −45°F | −46 to −43°C | Northern Plains |
| Zone 3a | −45 to −40°F | −43 to −40°C | International Falls, MN |
| Zone 3b | −40 to −35°F | −40 to −37°C | Fargo, ND; Duluth, MN |
| Zone 4a | −35 to −30°F | −37 to −34°C | Minneapolis, MN; Burlington, VT |
| Zone 4b | −30 to −25°F | −34 to −32°C | Portland, ME; Bozeman, MT |
| Zone 5a | −25 to −20°F | −32 to −29°C | Chicago, IL; Denver, CO |
| Zone 5b | −20 to −15°F | −29 to −26°C | Columbus, OH; Providence, RI |
| Zone 6a | −15 to −10°F | −26 to −23°C | St. Louis, MO; Louisville, KY |
| Zone 6b | −10 to −5°F | −23 to −21°C | Baltimore, MD; Kansas City, MO |
| Zone 7a | −5 to 0°F | −21 to −18°C | Washington DC; Nashville, TN |
| Zone 7b | 0 to 5°F | −18 to −15°C | Charlotte, NC; Albuquerque, NM |
| Zone 8a | 5 to 10°F | −15 to −12°C | Seattle, WA; Savannah, GA |
| Zone 8b | 10 to 15°F | −12 to −9°C | Portland, OR; Dallas, TX |
| Zone 9a | 15 to 20°F | −9 to −7°C | Sacramento, CA; Phoenix, AZ |
| Zone 9b | 20 to 25°F | −7 to −4°C | Los Angeles, CA; Tampa, FL |
| Zone 10a | 25 to 30°F | −4 to −1°C | Miami, FL; San Diego, CA |
| Zone 10b | 30 to 35°F | −1 to 2°C | South Florida; coastal Hawaii |
| Zone 11a | 35 to 40°F | 2 to 4°C | Hawaii (lower elevations) |
| Zone 11b | 40 to 45°F | 4 to 7°C | Hawaii (Kona coast) |
| Zone 12a | 45 to 50°F | 7 to 10°C | Puerto Rico |
| Zone 12b | 50 to 55°F | 10 to 13°C | Puerto Rico (low elevation) |
| Zone 13a | 55 to 60°F | 13 to 16°C | Puerto Rico (tropical lowlands) |
Source: USDA Agricultural Research Service Plant Hardiness Zone Map (2023)
The 2023 Map Update: What Changed for Half the Country
In November 2023, the USDA released its first updated Plant Hardiness Zone Map since 2012. The changes were significant:
The most visible change: large portions of Zone 6b shifted to Zone 7a, and Zone 7a areas moved to 7b. If you've been gardening by a zone number you looked up years ago, it's worth re-checking — your zone may have changed.
The USDA emphasized that the shift is primarily due to using more recent data and a denser station network, not a formal attribution to climate change. However, the practical implication is the same: many gardeners can now reliably grow plants that were marginally cold-tender in their old zone.
New zones 12 and 13 were added to the 2023 map for tropical areas of Hawaii and Puerto Rico that experience no meaningful winter cold. If you're in the continental US, you're in zones 1–10.
How to Find Your Exact Zone
There are three ways, in order of accuracy:
- 1
Use the ZIP code tool above (or on this page)
This pulls your zone from the same 2023 USDA dataset — accurate to your specific ZIP code, not just a regional approximation.
- 2
USDA's official interactive map at planthardiness.ars.usda.gov
Enter any ZIP code for the official answer. The site also lets you click any point on a detailed map, useful for rural areas between ZIP codes.
- 3
Read the printed zone on plant labels
Nursery tags typically say "Hardy to Zone X." Cross-reference with your zone to know whether the plant should survive your winters.
One important caveat: your ZIP code gives you the official zone for your area, but your specific yard may be measurably warmer or colder depending on microclimates (covered in the next section). The ZIP-code zone is the baseline — your actual conditions may differ.
What Hardiness Zones Do — and Don't — Tell You
The single biggest source of confusion about zones is using them for things they weren't designed for. Here's the quick breakdown:
✓ What zones ARE for
- ✓ Use it to choose perennials — trees, shrubs, roses, and perennial flowers that must survive your winters
- ✓ Use it to select fruit trees — apple, peach, cherry, and pear varieties are all rated by hardiness zone
- ✓ Use it to select lavender, rosemary, and other Mediterranean herbs that are borderline-hardy
- ✓ Use it as a reference when reading plant labels and nursery catalogs
✗ What zones are NOT for
- ✗ Use it to schedule planting dates — that's what last frost dates are for
- ✗ Rely on it for annuals (tomatoes, peppers, basil) — they grow in every zone; timing is what matters
- ✗ Assume your entire property is one zone — microclimates can vary by a full zone within a single yard
- ✗ Ignore summer heat — zones measure only winter cold, not heat, humidity, or drought
To put it bluntly: if you're trying to figure out when to plant tomatoes, peppers, or cucumbers, your USDA zone is almost irrelevant. Those are annual vegetables that grow in every zone from 2 to 11. What matters is your last frost date — the date after which it's safe to put tender transplants outside. Look that up separately.
Zone vs. Frost Date: Understanding the Difference
These two numbers are often confused, but they answer completely different questions:
| Question | USDA Hardiness Zone | Last Frost Date |
|---|---|---|
| What it measures | Average annual minimum winter temperature | Average date of last 28°F freeze in spring |
| Based on | 30 years of extreme low temperature records | 30 years of spring frost occurrence data (NOAA) |
| Used for | Choosing perennials that survive winter | Scheduling seed starts, transplant dates, direct sowing |
| Changes by location | Changes slowly over many miles | Can change by 2–3 weeks within a single county |
| Example | Zone 6a: winters average −15 to −10°F | Nashville, TN: average last frost April 3 |
A common illustration: Seattle (Zone 8b) and Birmingham, AL (Zone 8b) are in the same hardiness zone. Both have mild winters that rarely dip below 10°F. But Seattle's last frost averages late February while Birmingham's averages late March — almost 5 weeks apart — because Seattle's maritime climate brings mild early springs and Birmingham's continental climate has more variable late-season cold. Same zone; very different planting calendars.
Microclimates: Why Your Garden May Be a Different Zone
Your official USDA zone is an average for your ZIP code area. Your actual garden can be a full zone warmer or colder depending on its physical features. Understanding microclimates is how experienced gardeners successfully grow plants rated one zone beyond their official zone — or why a plant in the "wrong" spot dies when it should have thrived.
South-facing brick wall
Masonry absorbs solar heat all day and radiates it at night, keeping temps 5–10°F warmer in winter.
Low-lying frost pocket
Cold air drains downhill and pools in depressions. A hollow 10 feet below a hillside can be 5–8°F colder on clear, still nights.
Urban heat island
Dense cities are measurably warmer than surrounding suburbs. Downtown Boston, for example, sits in Zone 7a despite surrounding Zone 6 suburbs.
Dense conifer windbreak
Wind dramatically accelerates heat loss from soil and plants. Blocking prevailing winter winds can reduce effective windchill by 5–15°F.
Large body of water
Lakes and coastlines buffer temperatures — cooler in summer, warmer in winter. Chicago's lakeshore neighborhoods are reliably half a zone warmer than neighborhoods 5 miles inland.
North-facing slope
Reduced sun exposure means slower soil warming in spring and faster heat loss in winter — effectively pushing the microclimate colder.
How to map your microclimates: On the first light frost of fall, walk your yard an hour after sunrise and note exactly where frost appears first (coldest spots) and where the ground is still bare (warmest spots). Do this a few times across the season and you'll have a reliable microclimate map of your own property.
How Hardiness Zones Apply to Real Plant Decisions
Here are concrete examples of how zones inform plant selection across different categories:
Fruit Trees
Apple trees require significant winter cold (called "chill hours") and most varieties are hardy to Zone 3–4. Peach trees are less cold-hardy (Zone 5–9) and many varieties die back below −15°F. Fig trees, popular in the Southeast, are typically hardy only to Zone 7–8 outdoors. Citrus requires Zone 9+ for in-ground growing. Hardiness zone is the first filter when selecting any fruit tree.
Perennial Herbs
Rosemary is perennial only in Zone 7+ (some varieties to Zone 6 with protection). Lavender (English types) is reliable to Zone 5. Thyme overwinters to Zone 4. Mint and chives are among the hardiest, surviving to Zone 3. If you're in Zone 5 or 6, rosemary will need to come indoors each winter — it's not a perennial in your climate regardless of what the catalog photo suggests.
Perennial Flowers & Shrubs
Knockout roses are bred to Zone 4. Hydrangeas vary dramatically by species — panicle hydrangeas survive Zone 3, while bigleaf types (H. macrophylla) are reliable only to Zone 5–6. Crepe myrtles bloom in Zone 7+ but die to the ground in Zone 6 winters (though they often re-sprout). Hardy hibiscus (Rose mallow) survives Zone 4. Every perennial purchase at the nursery should start with "what zone is this rated for?"
Vegetables (Where Zone Doesn't Apply)
Tomatoes grow in every zone from 2 to 11. Kale, spinach, and broccoli can be grown coast to coast. For vegetable timing, you need your growing season — specifically, your last spring frost and first fall frost dates. Use our planting calendar for Zone 5a tomatoes, Zone 7b peppers, Zone 6a kale, or search by your state for California or Texas planting dates.
Other Zone Systems: AHS Heat Zones & Sunset Zones
The USDA hardiness map is the most widely used system in the US, but it has known limitations. Two other systems address things the USDA map misses:
AHS Plant Heat Zone Map
Developed by the American Horticultural Society, heat zones measure the average number of days per year when temperatures exceed 86°F (the threshold at which many plants experience heat damage). The map has 12 heat zones, with Zone 1 being coolest (under 1 day above 86°F) and Zone 12 being hottest (210+ days above 86°F).
Best for: Gardeners in the South and Southwest who can grow winter-cold-hardy plants but struggle with summer heat damage to cool-season crops.
Sunset Climate Zones
The Sunset Western Garden Book's 45-zone system is widely used in western states because it captures factors the USDA map ignores: summer heat, humidity, ocean influence, elevation, growing season length, and rainfall patterns. A Los Angeles coastal garden and a Los Angeles inland valley garden are both Zone 10 on the USDA map but dramatically different Sunset zones.
Best for: Western US gardeners, particularly in California, Oregon, and Washington where the USDA map oversimplifies highly varied microclimates.
For most US gardeners outside the West, the USDA hardiness zone combined with your last frost date gives you 90% of what you need to make good plant choices.
5 Common Hardiness Zone Mistakes
Checking an outdated zone
If you looked up your zone before November 2023, it may have changed. The 2023 update shifted about half the US warmer. Re-check your ZIP code on the current USDA map or using the tool above.
Using zone to schedule vegetable planting
Zone tells you winter cold, not when spring arrives. A Zone 6 gardener in Kansas City and a Zone 6 gardener in Philadelphia have very different last frost dates and growing seasons. Always use last frost dates for vegetable timing.
Treating the zone boundary as a hard line
Zone lines on the map represent averages. In any given year, a Zone 5 garden might experience Zone 6 conditions — or Zone 4. Winters 1–2 zones colder than average occur periodically. For marginally-hardy plants, build in a buffer.
Ignoring microclimates in your own yard
The official zone is for your ZIP code area, not your specific garden. A sheltered south-facing corner can be a full zone warmer than your official zone. Frost pockets in low spots can be a zone colder. Site matters as much as zone.
Trusting printed plant tags without verifying
Plant labels aren't always accurate. Some are set for the nursery's origin region, not your climate. When in doubt, cross-reference with university cooperative extension resources, which are calibrated to regional conditions.
Using Zone Data for Vegetable Planting Dates
This site uses USDA hardiness zone data as one of several inputs to generate personalized planting calendars. Enter your ZIP code and select a plant, and the calculator combines your zone, your specific last frost date, and the plant's biology to output seed-starting and transplant dates calibrated to your location.
You can also browse by zone directly. Each zone page shows planting windows for every plant in the database, derived from the typical last frost date for that zone:
- → Zone 4a tomato planting dates
- → Zone 5b pepper planting dates
- → Zone 6b cucumber planting dates
- → Zone 7a basil planting dates
- → Zone 8a broccoli planting dates
- → Zone 9b kale planting dates
For a complete breakdown of when to start seeds indoors, see our seed-starting guide, which lists indoor start times for 70+ plants calculated from your last frost date.
Frequently Asked Questions
What does a USDA hardiness zone number actually mean? +
Each zone represents a 10°F range of average annual minimum winter temperature. Zone 5, for example, covers areas where the coldest night of the year averages between −20°F and −10°F. Perennial plants labeled "hardy to Zone 5" are bred to survive that level of winter cold. The "a" and "b" subdivisions split each zone into two 5°F halves — 5a is colder (−25 to −20°F) and 5b is warmer (−20 to −15°F).
How do I find my USDA hardiness zone? +
The most accurate way is to enter your ZIP code into the USDA's official zone lookup at planthardiness.ars.usda.gov, which uses detailed weather station data. You can also use the ZIP-code tool on this page to find your zone alongside plant-specific planting dates for your location.
What changed in the 2023 USDA zone map update? +
The November 2023 update refreshed the map to use 1991–2020 temperature data (vs. 1976–2005 in the 2012 edition) and expanded the network from 7,983 to 13,412 weather stations. About half of the US shifted into a warmer half-zone — for example, parts of Zone 6b moved to 7a. The USDA notes this reflects more recent temperature patterns but is not officially attributed to climate change.
Is hardiness zone the same as planting zone? +
No. "Hardiness zone" specifically refers to the USDA system measuring average annual minimum winter temperature — it tells you whether a perennial will survive your winters. "Planting zone" is an informal term sometimes used to mean the same thing, but it's also used loosely to mean frost-date windows or growing seasons. For scheduling when to sow seeds and transplant, you need your last frost date, not just your USDA zone.
Can I grow plants rated for a warmer zone? +
Sometimes. If a plant is rated Zone 7 and you're in Zone 6, you may be able to grow it in a sheltered microclimate (against a south-facing wall, in a protected courtyard), with heavy winter mulching, or in a container you bring indoors. These techniques effectively push your growing conditions into the next warmer zone. However, in harsh winters the plant may still die back.
Why doesn't hardiness zone tell me when to plant vegetables? +
USDA hardiness zones measure only one thing: average annual minimum winter temperature. Vegetables like tomatoes, peppers, and cucumbers don't overwinter — they grow from seed to harvest each season. What matters for scheduling them is your last spring frost date and first fall frost date, which define your growing season. Two cities in the same zone can have very different growing seasons if one has long, cool summers and the other has short, hot ones.
What is a microclimate and how does it affect my zone? +
A microclimate is a small area where temperature, humidity, or wind conditions differ significantly from the surrounding region. South-facing walls, urban centers, frost pockets in low-lying areas, and lakeshores all create microclimates. Your backyard microclimate can be a full zone warmer or colder than your official USDA zone. Observing where frost forms last each spring is one of the best ways to identify the warmest spots in your garden.
Get Your Zone-Specific Planting Calendar
Now that you know your zone, get exact planting dates for tomatoes, peppers, cucumbers, and 140+ more plants — calculated for your specific ZIP code and last frost date.
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