March 7, 2026 · 8 min read
Your USDA plant hardiness zone (also called "grow zone" or "planting zone") is a geographic area defined by average annual minimum winter temperatures. It tells you which plants can survive winter in your area.
Quick Answer: Visit planthardiness.ars.usda.gov and enter your ZIP code to find your zone instantly.
The 13 USDA Hardiness Zones (Quick Reference)
- Zone 1: -60 to -50°F (Northern Alaska)
- Zone 2: -50 to -40°F (Central Alaska, northern MN)
- Zone 3: -40 to -30°F (Northern MN, ND, MT)
- Zone 4: -30 to -20°F (Minneapolis, Buffalo, Boise)
- Zone 5: -20 to -10°F (Chicago, Boston, Denver)
- Zone 6: -10 to 0°F (NYC, Philadelphia, St. Louis)
- Zone 7: 0 to 10°F (Washington DC, Memphis, OKC)
- Zone 8: 10 to 20°F (Dallas, Atlanta, Seattle)
- Zone 9: 20 to 30°F (Houston, Phoenix, LA)
- Zone 10: 30 to 40°F (Miami, San Diego, SoCal)
- Zone 11: 40 to 50°F (Hawaii, Key West)
- Zone 12: 50 to 60°F (Southern Hawaii, Puerto Rico)
- Zone 13: 60 to 70°F (Tropical Hawaii only)
Example: If you're in Zone 6, your average coldest winter temperature is between 0°F and -10°F. This means perennial plants rated for Zone 6 or lower will survive your winters. Plants rated Zone 7+ may die in winter cold.
How to Find Your Exact Zone (3 Methods)
Method 1: Official USDA Website (Most Accurate)
- Visit planthardiness.ars.usda.gov
- Enter your ZIP code in the search box
- View your zone on the interactive map
- Bonus: Click "GeoLocation" to auto-detect based on your current location
Method 2: Mobile Apps
- USDA Plant Hardiness Zone Finder (iOS/Android) - Free official app
- Garden Answers - Includes zone finder + plant ID
- Old Farmer's Almanac Garden Planner - Zone lookup + planting calendar
Method 3: Interactive Zone Map
- USDA Interactive Map: Zoom in to see micro-zones in your area
- Arbor Day Foundation: Updated zone map (2012 version, 5°F warmer than 1990)
- PlantMaps.com: Alternative zone finder with city search
Understanding Zone Subdivisions (a vs b)
Most zones are divided into a and b subzones, each covering 5°F:
Example: Zone 6
- Zone 6a: -10°F to -5°F (colder half)
- Zone 6b: -5°F to 0°F (warmer half)
Why it matters: A plant rated "Zone 6" will survive in both 6a and 6b. But a plant rated "Zone 6b-9" might struggle in Zone 6a.
What Your Zone Tells You (and What It Doesn't)
What Zones DO Tell You:
- Winter survival: Which perennials, trees, and shrubs can survive your coldest temps
- Plant selection: What to buy at the nursery (most plants labeled with zones)
- Baseline climate: General idea of your growing conditions
What Zones DON'T Tell You:
- Summer heat: Arizona and North Carolina are both Zone 8, but very different summers
- Humidity: Dry desert vs humid subtropical zones aren't distinguished
- Rainfall: Seattle and Denver are similar zones but drastically different precipitation
- Frost dates: Zones don't tell you when to plant (see Last Frost Dates Guide)
- Microclimate: Your yard might be a zone warmer/colder than your ZIP code average
Microclimates: Why Your Yard Might Be Different
Your actual growing zone can vary from the ZIP code average:
Warmer Microclimates (Effectively 1 zone warmer)
- Urban areas: Cities are 5-10°F warmer (heat island effect)
- South-facing walls: Reflect heat, protect from cold wind
- Stone/concrete: Absorbs heat during day, releases at night
- Near water: Large bodies of water moderate temperatures
Colder Microclimates (Effectively 1 zone colder)
- Valleys/low spots: Cold air sinks and pools
- Dense shade: Less sun = colder soil
- Exposed hilltops: Wind chill lowers effective temps
- Elevation: Every 1,000 feet = ~3°F colder
Pro tip: Create a microclimate map of your yard! Plant tender plants near warm south walls, hardy plants in exposed areas.
Using Your Zone: Practical Examples
At the Nursery
Plant tag says "Hardy in Zones 5-9":
- You're in Zone 6? ✅ Perfect, plant it!
- You're in Zone 4? ❌ It'll die in winter
- You're in Zone 10? ❌ It needs colder winters (won't thrive)
Shopping Online
Seed catalog says "Zone 3-7":
- You're in Zone 8? Don't buy it (too warm, plant won't get required winter chill)
- You're in Zone 5? Buy with confidence
Planting Calendar
Once you know your zone, you can determine:
- Last spring frost date: When to plant tender annuals
- First fall frost date: When to harvest/protect plants
- Growing season length: Days between frosts
See Complete Frost Date Calendar →
Zone Shifting: Climate Change Impact
Hardiness zones have shifted ~5°F warmer over the past 30 years:
- Parts of Illinois moved from Zone 5 → Zone 6
- Southern California zones shifted half a zone warmer
- Northern states gained 10-20 days of growing season
What this means: You may be able to grow plants that were previously "too tender" for your area. But also expect more heat stress on traditionally cold-adapted plants.
Quick Zone Lookup by Major City
- Anchorage, AK: 4b
- Atlanta, GA: 8a
- Boston, MA: 6b
- Chicago, IL: 6a
- Dallas, TX: 8a
- Denver, CO: 5b
- Detroit, MI: 6b
- Houston, TX: 9a
- Los Angeles, CA: 10a
- Miami, FL: 10b
- New York, NY: 7b
- Philadelphia, PA: 7a
- Phoenix, AZ: 9b
- Portland, OR: 8b
- San Diego, CA: 10b
- San Francisco, CA: 10a
- Seattle, WA: 8b
- St. Louis, MO: 6b
- Tampa, FL: 9b
- Washington, DC: 7b
Bottom Line
Finding your zone takes 30 seconds. Using it correctly takes practice. Zones are a guideline, not a guarantee. Factor in microclimates, heat zones, and local conditions. When in doubt, ask neighboring gardeners what grows well for them!
Next Steps: