Denver, Colorado: planting zone & frost dates
Denver is in USDA plant hardiness zone 6a, where the average coldest winter night reaches -10 to -5°F (-23.3 to -20.6°C). The typical last spring frost is around May 8 and the first fall frost around Oct 3.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | May 16 | Sep 25 |
| Typical planning date (30% risk) | May 8 | Oct 3 |
| Median (50%) | May 4 | Oct 8 |
How to read this: after the spring "10% risk" date, a 32°F frost happens in only about 1 year in 10. In fall, the "10% risk" date is the early end — a frost before it happens about 1 year in 10.
Frost data comes from NOAA station DENVER-STAPLETON, CO (USW00023062), 0.6 mi (1.0 km) from the city center and 7 ft lower than the city center (-2 m). Record used for the 1991–2020 normals: 28 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Denver
All 30 ZIP codes covering Denver are in zone 6a.
ZIP codes in Denver and their zones
| ZIP | Zone | Share of city land |
|---|---|---|
| 80249 | 6a | 31.1% |
| 80239 | 6a | 5.4% |
| 80216 | 6a | 4.8% |
| 80219 | 6a | 4.8% |
| 80238 | 6a | 4.4% |
| 80210 | 6a | 4.0% |
| 80204 | 6a | 3.6% |
| 80223 | 6a | 3.5% |
| 80220 | 6a | 3.4% |
| 80205 | 6a | 3.0% |
| 80211 | 6a | 2.9% |
| 80207 | 6a | 2.6% |
| 80237 | 6a | 2.4% |
| 80209 | 6a | 2.3% |
| 80222 | 6a | 2.1% |
| 80224 | 6a | 2.1% |
| 80236 | 6a | 2.0% |
| 80231 | 6a | 1.9% |
| 80212 | 6a | 1.7% |
| 80206 | 6a | 1.6% |
| 80230 | 6a | 1.6% |
| 80123 | 6a | 1.5% |
| 80218 | 6a | 1.0% |
| 80227 | 6a | 1.0% |
| 80247 | 6a | 1.0% |
| 80202 | 6a | 0.8% |
| 80203 | 6a | 0.7% |
| 80246 | 6a | 0.7% |
| 80266 | 6a | 0.1% |
| 80290 | 6a | 0.0% |
Vegetable planting calendar for Denver
Dates are counted from the 30%-risk frost dates above (last frost May 8, first frost Oct 3). Shift a week later in cold spots or low-lying ground.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato | Mar 13 – Mar 27 | May 15 – May 29 | — | — |
| Pepper | Feb 27 – Mar 13 | May 22 – Jun 5 | — | — |
| Lettuce | Mar 27 – Apr 10 | Apr 24 – May 15 | Apr 10 – May 22 | Jul 25 – Aug 22 |
| Green Beans | — | — | May 15 – Jun 19 | Jul 11 – Jul 25 |
| Sweet Corn | — | — | May 15 – Jun 12 | — |
| Zucchini & Summer Squash | Apr 10 – Apr 17 | May 15 – May 29 | May 15 – Jun 5 | Jul 11 – Jul 25 |
| Cucumber | Apr 10 – Apr 17 | May 22 – May 29 | May 15 – Jun 5 | Jul 11 – Jul 25 |
| Carrot | — | — | Apr 17 – May 22 | Jul 11 – Jul 25 |
| Onion | Feb 13 – Feb 27 | Apr 10 – Apr 24 | — | — |
| Potato | — | Apr 10 – May 1 | — | — |
| Basil | Mar 27 – Apr 10 | May 22 – Jun 5 | May 22 – Jun 12 | — |
| Spinach | — | — | Mar 27 – Apr 24 | Aug 8 – Sep 5 |
| Kale | Mar 13 – Mar 27 | Apr 10 – May 1 | Apr 10 – May 1 | Jul 25 – Aug 22 |
| Broccoli | Mar 13 – Mar 27 | Apr 24 – May 15 | — | Jul 11 – Jul 25 |
| Peas | — | — | Mar 27 – Apr 17 | Jul 25 – Aug 8 |
| Eggplant | Feb 27 – Mar 13 | May 22 – Jun 5 | — | — |
| Cabbage | Mar 13 – Mar 27 | Apr 10 – Apr 24 | — | Jul 11 – Jul 25 |
| Radish | — | — | Apr 3 – May 22 | Aug 22 – Sep 19 |
| Strawberry | — | Apr 10 – May 1 | — | — |
| Beets | — | — | Apr 17 – May 29 | Jul 25 – Aug 8 |
Nearby cities in Colorado
- Aurora — zone 6a, last frost May 12, first frost Oct 2
- Thornton — zone 6a, last frost May 7, first frost Oct 4
- Centennial — zone 6a, last frost May 10, first frost Oct 3
- Westminster — zone 6a, last frost May 7, first frost Oct 4
- Lakewood — zone 6a, last frost May 8, first frost Oct 2
- Broomfield — zone 6a, last frost May 7, first frost Oct 4
More: all Colorado cities · other zone 6a cities: Chicago, IL, Milwaukee, WI, Colorado Springs, CO, Omaha, NE, Aurora, CO, Lincoln, NE, Fort Wayne, IN, Worcester, MA
Denver gardening questions
When is the last frost in Denver, CO?
Plan around May 8. At NOAA's Denver-stapleton, CO station, 0.6 mi from the city center, there is a 30% chance of a 32°F frost after that date. Half of springs have their last frost by May 4, and after May 16 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Apr 22. The last frost is fairly predictable here: only 26 days separate the 90% and 10% dates (median for cities on this site: 36 days).
When should I plant tomatoes in Denver, CO?
Start seeds indoors Mar 13 – Mar 27 and set transplants outside May 15 – May 29, once nights stay above 50°F and the soil is near 60°F. That leaves 148 days between the 30% frost dates, enough for most varieties including 80–85-day slicers. More: tomato planting dates by zone.
How long is the growing season in Denver?
About 156 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 138 days, and in 1 year in 10 it runs 175 days or more. In fall there is a 10% chance of frost by Sep 25 and a 30% chance by Oct 3. That ranks 8th longest of 16 Colorado cities on this site.
When should I plant a fall garden in Denver?
Count back from the first fall frost (Oct 3): transplant broccoli Jul 11 – Jul 25; sow kale Jul 25 – Aug 22; sow lettuce Jul 25 – Aug 22; sow radishes Aug 22 – Sep 19. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Oct 18. How the math works: succession and fall planting.
Did Denver's hardiness zone change on the 2023 map?
Yes. Most of Denver was zone 5b on the 2012 map and is zone 6a on the 2023 map — half a zone warmer, like about 56% of U.S. ZIP codes. The shift comes from a newer 1991–2020 averaging period plus more weather stations and better mapping; it does not mean last frost comes earlier. Why the 2023 map is warmer.
How does Denver compare with Aurora, CO?
Both are in zone 6a. The typical last spring frost in Denver (May 8) comes about 4 days earlier than in Aurora, CO (May 12), 9 miles away, and the first fall frost is Oct 3 versus Oct 2. Denver sits about 252 ft lower, which explains part of the gap. The two cities use different NOAA stations.