When Is the Last Frost in Colorado?
The average last spring frost in Colorado falls between April 30 and June 12 for most ZIP codes, with a statewide median of May 9. At the average date a later frost is still a coin flip, so tender plants wait for the safer 90% date.
| City | Last frost | 90% safe after | First frost | Growing season |
|---|---|---|---|---|
| Denver | May 4 | May 16 | Oct 8 | 156 days |
| Colorado Springs | May 3 | May 15 | Oct 8 | 158 days |
| Aurora | May 5 | May 19 | Oct 9 | 156 days |
| Fort Collins | May 3 | May 15 | Oct 6 | 154 days |
| Lakewood | May 3 | May 18 | Oct 7 | 155 days |
| Thornton | May 2 | May 14 | Oct 11 | 160 days |
| Arvada | May 5 | May 18 | Oct 5 | 151 days |
| Westminster | May 2 | May 14 | Oct 11 | 160 days |
| Greeley | May 2 | May 14 | Oct 8 | 159 days |
| Pueblo | Apr 26 | May 8 | Oct 13 | 166 days |
| Longmont | May 7 | May 22 | Oct 5 | 151 days |
| Castle Rock | May 9 | May 24 | Oct 2 | 143 days |
| Grand Junction | Apr 14 | Apr 28 | Oct 23 | 190 days |
| Montrose | May 20 | Jun 4 | Oct 1 | 132 days |
| Durango | Jun 1 | Jun 15 | Sep 27 | 116 days |
| Cañon City | May 4 | May 18 | Oct 7 | 153 days |
| Steamboat Springs | Jun 9 | Jun 24 | Sep 12 | 93 days |
| Sterling | Apr 30 | May 12 | Oct 9 | 161 days |
| Eaton | May 2 | May 14 | Oct 8 | 159 days |
Last and first frost: 50% (median) dates of the last spring and first fall 32 °F night. 90% safe after: only a 10% chance of a later spring frost. First frost dates in January fall in the following winter. Each city uses the NOAA station nearest the ZIP code closest to its center.
Across all 210 Colorado weather stations with frost records, median last frost dates run from April 14 at Grand Junction WFO, CO to June 21 at Cochetopa Creek, CO. Elevation, valleys that collect cold air and distance from large water bodies explain most of the spread, so a garden a few miles from a listed city can differ by a week or more. The ZIP code lookup above uses the same NOAA data as the frost date calculator for every US ZIP code.
When Is the First Frost in Colorado?
The average first fall frost in Colorado arrives between September 11 and October 12 for most ZIP codes, with a median of October 5. Tomatoes, peppers, basil and squash are damaged at 32 °F, so harvest or cover them before then.
Fall frost can come early: Denver has a 10% chance of frost before September 25, Colorado Springs has a 10% chance of frost before September 26 and Aurora has a 10% chance of frost before September 27. Hardy crops such as kale, spinach and cabbage tolerate light frosts and keep producing after the first frost date.
When to Plant Tomatoes in Colorado?
Transplant tomatoes in Colorado 1 to 2 weeks after the local average last frost, once nights stay above about 50 °F: May 11 – May 18 in Denver, May 10 – May 17 in Colorado Springs and May 12 – May 19 in Aurora. Start seeds indoors 6 to 8 weeks before the last frost.
| City | Start seeds indoors | Transplant outdoors | Lowest-risk transplant |
|---|---|---|---|
| Denver | Mar 9 – Mar 23 | May 11 – May 18 | after May 16 |
| Colorado Springs | Mar 8 – Mar 22 | May 10 – May 17 | after May 15 |
| Aurora | Mar 10 – Mar 24 | May 12 – May 19 | after May 19 |
| Fort Collins | Mar 8 – Mar 22 | May 10 – May 17 | after May 15 |
| Lakewood | Mar 8 – Mar 22 | May 10 – May 17 | after May 18 |
| Thornton | Mar 7 – Mar 21 | May 9 – May 16 | after May 14 |
| Arvada | Mar 10 – Mar 24 | May 12 – May 19 | after May 18 |
| Westminster | Mar 7 – Mar 21 | May 9 – May 16 | after May 14 |
| Greeley | Mar 7 – Mar 21 | May 9 – May 16 | after May 14 |
| Pueblo | Mar 1 – Mar 15 | May 3 – May 10 | after May 8 |
| Longmont | Mar 12 – Mar 26 | May 14 – May 21 | after May 22 |
| Castle Rock | Mar 14 – Mar 28 | May 16 – May 23 | after May 24 |
| Grand Junction | Feb 17 – Mar 3 | Apr 21 – Apr 28 | after Apr 28 |
| Montrose | Mar 25 – Apr 8 | May 27 – Jun 3 | after Jun 4 |
| Durango | Apr 6 – Apr 20 | Jun 8 – Jun 15 | after Jun 15 |
| Cañon City | Mar 9 – Mar 23 | May 11 – May 18 | after May 18 |
| Steamboat Springs | Apr 14 – Apr 28 | Jun 16 – Jun 23 | after Jun 24 |
| Sterling | Mar 5 – Mar 19 | May 7 – May 14 | after May 12 |
| Eaton | Mar 7 – Mar 21 | May 9 – May 16 | after May 14 |
Indoors: 6–8 weeks before the average last frost. Outdoors: 1–2 weeks after it. Lowest-risk: after the date with only a 10% chance of a later frost. Rules of thumb; check the 10-day forecast and wait for soil near 60 °F.
Tomatoes stall below about 50 °F at night and are killed by frost, so a week or two of waiting after the average date costs little. The tomato plant care guide covers light, watering and feeding once plants are in the ground.
What Can You Plant in Denver and When?
Denver's average last frost of May 4 anchors its spring planting calendar: peas and spinach go in from March 23, broccoli and lettuce transplants from April 6, and tomatoes, peppers and squash after May 11.
| Crop | Start seeds indoors | Plant outdoors | Frost tolerance |
|---|---|---|---|
| Peas | — | Mar 23 – Apr 6direct sow, 4–6 weeks before last frost | hardy |
| Spinach | — | Mar 23 – Apr 13direct sow, 3–6 weeks before last frost | hardy |
| Radishes | — | Mar 30 – Apr 13direct sow, 3–5 weeks before last frost | hardy |
| Onions (sets) | — | Apr 6 – Apr 20plant, 2–4 weeks before last frost | hardy |
| Potatoes | — | Apr 6 – Apr 20plant, 2–4 weeks before last frost | half-hardy |
| Broccoli & cabbage | Mar 9 – Mar 23 | Apr 6 – Apr 20transplant, 2–4 weeks before last frost | hardy |
| Lettuce | Mar 23 – Apr 6 | Apr 6 – Apr 20transplant, 2–4 weeks before last frost | hardy |
| Beets | — | Apr 6 – Apr 20direct sow, 2–4 weeks before last frost | half-hardy |
| Carrots | — | Apr 13 – Apr 20direct sow, 2–3 weeks before last frost | half-hardy |
| Tomatoes | Mar 9 – Mar 23 | May 11 – May 18transplant, 1–2 weeks after last frost | tender |
| Basil | Mar 9 – Mar 23 | May 11 – May 25transplant, 1–3 weeks after last frost | tender |
| Peppers | Feb 23 – Mar 9 | May 18 – May 25transplant, 2–3 weeks after last frost | tender |
| Eggplant | Feb 23 – Mar 9 | May 18 – May 25transplant, 2–3 weeks after last frost | tender |
| Green beans | — | May 11 – May 25direct sow, 1–3 weeks after last frost | tender |
| Sweet corn | — | May 11 – May 25direct sow, 1–3 weeks after last frost | tender |
| Cucumbers | Apr 6 – Apr 13 | May 11 – May 25transplant, 1–3 weeks after last frost | tender |
| Squash & zucchini | Apr 6 – Apr 13 | May 11 – May 25transplant, 1–3 weeks after last frost | tender |
| Watermelon | Apr 6 – Apr 13 | May 18 – May 25transplant, 2–3 weeks after last frost | tender |
Dates for Denver (last frost May 4, NOAA station Denver-Stapleton, CO, under 1 mile from ZIP 80238). General rules of thumb; wait for soil near 50 °F for most seeds and 60 °F for beans, corn and squash.
How Long Is the Growing Season in Colorado?
The frost-free growing season in Colorado lasts about 89 to 164 days for most ZIP codes, with a median of 149 days. Among the listed cities, Steamboat Springs has the shortest season at 93 days and Grand Junction the longest at 190.
Season length decides which varieties ripen: compare it with the “days to maturity” on seed packets, counted from transplanting for tomatoes and peppers. NOAA stations in Colorado range from 71 days at Boulder 14 W, CO to 190 days at Grand Junction WFO, CO. Planning beds before the season starts helps in short seasons — a plant spacing calculator for vegetable beds shows how many transplants fit.
What Hardiness Zones Are in Colorado?
Colorado spans USDA hardiness zones 4a to 7a, with zone 6a the most common. Zones describe winter cold and decide which perennials survive, while frost dates set when to plant annual vegetables and flowers.
The Colorado planting zone map with the zone of each city shows how the zones are spread across the state and which plants are hardy in all of them.
Frequently Asked Questions
- When is the last frost in Colorado?
- The average last spring frost in Colorado falls between April 30 and June 12 for most ZIP codes, with a statewide median of May 9. Among major cities it ranges from April 14 in Grand Junction to June 9 in Steamboat Springs.
- When is the last frost in Denver, Colorado?
- Denver's average last spring frost is May 4, and by May 16 the chance of a later frost drops to 10%. Its first fall frost averages October 8, giving a 156-day growing season (NOAA station Denver-Stapleton, CO).
- When should you plant tomatoes in Colorado?
- Transplant tomatoes in Colorado 1 to 2 weeks after the local average last frost, once nights stay above about 50 °F: May 11 – May 18 in Denver, May 10 – May 17 in Colorado Springs and May 12 – May 19 in Aurora. Start seeds indoors 6 to 8 weeks before the last frost.
- When is the first frost in Colorado?
- The average first fall frost in Colorado arrives between September 11 and October 12 for most ZIP codes, with a median of October 5. Harvest tender crops such as tomatoes, peppers and basil before then or cover them on cold nights.
- How long is the growing season in Colorado?
- The frost-free growing season in Colorado lasts about 89 to 164 days for most ZIP codes, with a median of 149 days, from 93 days in Steamboat Springs to 190 days in Grand Junction.
Frost data: NOAA National Centers for Environmental Information, 1991–2020 U.S. Climate Normals (32 °F freeze dates by probability). ZIP code and city locations and populations: U.S. Census Bureau Gazetteer files and Vintage 2024 population estimates. Planting windows are general rules of thumb. PlantoScan is not affiliated with or endorsed by these agencies.