What Planting Zones Are in Colorado?
Colorado spans USDA hardiness zones 4a to 7a, where the average coldest winter night ranges from −30 °F to 5 °F (−34.4 °C to −15 °C). Zone 6a covers the most ZIP codes, 44%, and zones 5a to 6a together cover 90% of the state.
- Zone 4a<1% · 2 ZIPs
- Zone 4b2% · 10 ZIPs
- Zone 5a12% · 73 ZIPs
- Zone 5b35% · 217 ZIPs
- Zone 6a44% · 274 ZIPs
- Zone 6b6% · 36 ZIPs
- Zone 7a2% · 13 ZIPs
Bars show each zone's share of the 625 Colorado ZIP codes in the official 2023 USDA ZIP code table; select a zone for its temperatures and hardy plants.
What Hardiness Zone Are Colorado Cities In?
Denver is in zone 6a, Colorado Springs is in zone 6a, Aurora is in zone 6a and Fort Collins is in zone 5b. The table lists the zone, winter low and average frost dates for 19 Colorado cities, using the ZIP code nearest each city center.
| City | ZIP | Zone | Winter low | Last frost | First frost |
|---|---|---|---|---|---|
| Denver | 80238 | 6a | −10 °F to −5 °F | May 4 | Oct 8 |
| Colorado Springs | 80909 | 6a | −10 °F to −5 °F | May 3 | Oct 8 |
| Aurora | 80018 | 6a | −10 °F to −5 °F | May 5 | Oct 9 |
| Fort Collins | 80525 | 5b | −15 °F to −10 °F | May 3 | Oct 6 |
| Lakewood | 80226 | 6a | −10 °F to −5 °F | May 3 | Oct 7 |
| Thornton | 80241 | 6a | −10 °F to −5 °F | May 2 | Oct 11 |
| Arvada | 80005 | 6a | −10 °F to −5 °F | May 5 | Oct 5 |
| Westminster | 80031 | 6a | −10 °F to −5 °F | May 2 | Oct 11 |
| Greeley | 80634 | 5b | −15 °F to −10 °F | May 2 | Oct 8 |
| Pueblo | 81003 | 6a | −10 °F to −5 °F | Apr 26 | Oct 13 |
| Longmont | 80501 | 5b | −15 °F to −10 °F | May 7 | Oct 5 |
| Castle Rock | 80109 | 5b | −15 °F to −10 °F | May 9 | Oct 2 |
| Grand Junction | 81501 | 7a | 0 °F to 5 °F | Apr 14 | Oct 23 |
| Montrose | 81401 | 6b | −5 °F to 0 °F | May 20 | Oct 1 |
| Durango | 81303 | 6b | −5 °F to 0 °F | Jun 1 | Sep 27 |
| Cañon City | 81244 | 6a | −10 °F to −5 °F | May 4 | Oct 7 |
| Steamboat Springs | 80487 | 5b | −15 °F to −10 °F | Jun 9 | Sep 12 |
| Sterling | 80751 | 5b | −15 °F to −10 °F | Apr 30 | Oct 9 |
| Eaton | 80615 | 5a | −20 °F to −15 °F | May 2 | Oct 8 |
Zone: 2023 USDA ZIP code table for the ZIP code nearest each city's Census center point. Frost dates: 50% (median) dates from the nearest NOAA station, 1991–2020 normals. Cities: the largest Colorado places by 2024 Census population estimates, spread across the state, plus the largest place in each common zone. Large cities can span two half zones.
Which Parts of Colorado Are in Each Zone?
Zone 4b, the coldest Colorado zone with towns, covers 2% of ZIP codes around Alamosa. Zone 7a, the warmest, covers 2% around Grand Junction, Fruita and Cortez. The table lists the largest places in every zone.
| Zone | Avg. coldest night | Share of ZIPs | Largest places in this zone |
|---|---|---|---|
| Zone 4a | −30 °F to −25 °F | <1% (2) | Rural ZIP codes only |
| Zone 4b | −25 °F to −20 °F | 2% (10) | Alamosa |
| Zone 5a | −20 °F to −15 °F | 12% (73) | Eaton, Estes Park, Silverthorne, Breckenridge |
| Zone 5b | −15 °F to −10 °F | 35% (217) | Fort Collins, Greeley, Longmont, Castle Rock |
| Zone 6a | −10 °F to −5 °F | 44% (274) | Denver, Colorado Springs, Aurora, Lakewood |
| Zone 6b | −5 °F to 0 °F | 6% (36) | Montrose, Durango, Delta, Orchard City |
| Zone 7a | 0 °F to 5 °F | 2% (13) | Grand Junction, Fruita, Cortez, Palisade |
Places: incorporated places with 1,000+ residents, assigned the zone of the ZIP code nearest their Census center point.
What Do the Hardiness Zones Mean for Colorado Gardeners?
A Colorado gardener in zone 7a sees winter lows about 30 °F milder than one in zone 4a, so a shrub or perennial that thrives in one part of the state can die in another. Choose plants rated to your own ZIP code's zone or colder.
Hardiness zones follow latitude, elevation and large bodies of water rather than state lines. Higher ground and inland valleys that trap cold air usually sit in colder half zones, while cities, coasts and large lakes moderate winter lows. Within Colorado, a plant labelled “zones 5–6” survives winter in at least 90% of ZIP codes, but plants at the edge of their range benefit from mulch and a sheltered spot. Enter a ZIP code in the USDA hardiness zone finder by ZIP code to check your exact half zone before buying perennials.
A zone describes winter cold only. Summer heat, humidity, rainfall and soil decide whether a cold-hardy plant thrives, and planting dates for vegetables follow frost dates, not zones: two Colorado towns in the same zone can have last frosts weeks apart.
What Plants Grow Well Across Colorado?
199 plants in PlantoScan's catalogue are hardy in every zone from 5a to 6a, the zones that cover 90% of Colorado ZIP codes. Popular examples include hydrangea, peony and daisy.
Hydrangea
Hydrangea macrophylla
Zone 5 – 9
AI generated
Peony
Paeonia lactiflora
Zone 3 – 8
AI generated
- DaisyBellis perennisPlantoScan
Daisy
Bellis perennis
Zone 4a – 8b
Chrysanthemum
Chrysanthemum morifolium
Zone 5a – 9b
PlantoscanAI generated
Poppy
Papaver somniferum
Zone 3a – 9b
AI generated
Carnation
Dianthus caryophyllus
Zone 5a – 9b
AI generated
Daffodil
Narcissus poeticus
Zone 3 – 8
AI generated
Arugula
Eruca sativa
Zone 5a – 10b
AI generated
Alfalfa
Medicago sativa
Zone 3a – 10a
AI generated
Hardiness ranges come from PlantoScan's plant database; gardeners in Colorado's colder or warmer edge zones should check each plant's full range.
When Is the Last Frost in Colorado?
Across most Colorado ZIP codes, the average last spring frost falls between April 30 and June 12, from April 14 in Grand Junction to June 9 in Steamboat Springs. Tender vegetables such as tomatoes go out 1 to 2 weeks after the local date.
The last and first frost dates for Colorado cities include the safer 90% planting date, the fall frost date, growing season length and a tomato planting table for each city.
Frequently Asked Questions
- What planting zone is Colorado?
- Colorado spans USDA hardiness zones 4a to 7a on the 2023 USDA Plant Hardiness Zone Map. Zone 6a is the most common, covering 44% of the state's 625 ZIP codes, and zones 5a to 6a together cover 90%.
- What hardiness zone is Denver, Colorado?
- Denver is in USDA hardiness zone 6a (ZIP 80238), where the average coldest winter night reaches −10 °F to −5 °F. Its average last spring frost is May 4 and its first fall frost October 8.
- What hardiness zone is Colorado Springs, Colorado?
- Colorado Springs is in USDA hardiness zone 6a (ZIP 80909), where the average coldest winter night reaches −10 °F to −5 °F. Its average last spring frost is May 3 and its first fall frost October 8.
- What hardiness zone is Aurora, Colorado?
- Aurora is in USDA hardiness zone 6a (ZIP 80018), where the average coldest winter night reaches −10 °F to −5 °F. Its average last spring frost is May 5 and its first fall frost October 9.
- What is the coldest hardiness zone in Colorado?
- Zone 4a (−30 °F to −25 °F) is the coldest zone in Colorado, found in 2 ZIP codes. The warmest is zone 7a (0 °F to 5 °F), around Grand Junction and Fruita.
Zones: 2023 USDA Plant Hardiness Zone Map ZIP code table, USDA Agricultural Research Service and the PRISM Climate Group, Oregon State University, used without changes. Frost dates: NOAA National Centers for Environmental Information, 1991–2020 U.S. Climate Normals. City locations and populations: U.S. Census Bureau Gazetteer files and Vintage 2024 population estimates. PlantoScan is not affiliated with or endorsed by these agencies.