Centennial, Colorado: planting zone & frost dates
Centennial 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 10 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 17 | Sep 25 |
| Typical planning date (30% risk) | May 10 | Oct 3 |
| Median (50%) | May 5 | 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 CENTENNIAL AP, CO (USW00093067), 1.6 mi (2.6 km) from the city center and 144 ft higher than the city center (+44 m). Record used for the 1991–2020 normals: 20 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Centennial
All 6 ZIP codes covering Centennial are in zone 6a.
Vegetable planting calendar for Centennial
Dates are counted from the 30%-risk frost dates above (last frost May 10, 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 15 – Mar 29 | May 17 – May 31 | — | — |
| Pepper | Mar 1 – Mar 15 | May 24 – Jun 7 | — | — |
| Lettuce | Mar 29 – Apr 12 | Apr 26 – May 17 | Apr 12 – May 24 | Jul 25 – Aug 22 |
| Green Beans | — | — | May 17 – Jun 21 | Jul 11 – Jul 25 |
| Sweet Corn | — | — | May 17 – Jun 14 | — |
| Zucchini & Summer Squash | Apr 12 – Apr 19 | May 17 – May 31 | May 17 – Jun 7 | Jul 11 – Jul 25 |
| Cucumber | Apr 12 – Apr 19 | May 24 – May 31 | May 17 – Jun 7 | Jul 11 – Jul 25 |
| Carrot | — | — | Apr 19 – May 24 | Jul 11 – Jul 25 |
| Onion | Feb 15 – Mar 1 | Apr 12 – Apr 26 | — | — |
| Potato | — | Apr 12 – May 3 | — | — |
| Basil | Mar 29 – Apr 12 | May 24 – Jun 7 | May 24 – Jun 14 | — |
| Spinach | — | — | Mar 29 – Apr 26 | Aug 8 – Sep 5 |
| Kale | Mar 15 – Mar 29 | Apr 12 – May 3 | Apr 12 – May 3 | Jul 25 – Aug 22 |
| Broccoli | Mar 15 – Mar 29 | Apr 26 – May 17 | — | Jul 11 – Jul 25 |
| Peas | — | — | Mar 29 – Apr 19 | Jul 25 – Aug 8 |
| Eggplant | Mar 1 – Mar 15 | May 24 – Jun 7 | — | — |
| Cabbage | Mar 15 – Mar 29 | Apr 12 – Apr 26 | — | Jul 11 – Jul 25 |
| Radish | — | — | Apr 5 – May 24 | Aug 22 – Sep 19 |
| Strawberry | — | Apr 12 – May 3 | — | — |
| Beets | — | — | Apr 19 – May 31 | Jul 25 – Aug 8 |
Nearby cities in Colorado
- Denver — zone 6a, last frost May 8, first frost Oct 3
- Aurora — zone 6a, last frost May 12, first frost Oct 2
- Castle Rock — zone 5b, last frost May 15, first frost Sep 27
- Lakewood — zone 6a, last frost May 8, first frost Oct 2
- Thornton — zone 6a, last frost May 7, first frost Oct 4
- Westminster — zone 6a, last frost May 7, first frost Oct 4
More: all Colorado cities · other zone 6a cities: Chicago, IL, Denver, CO, Milwaukee, WI, Colorado Springs, CO, Omaha, NE, Aurora, CO, Lincoln, NE, Fort Wayne, IN
Centennial gardening questions
When is the last frost in Centennial, CO?
Plan around May 10. At NOAA's Denver Centennial Airport, CO station, 1.6 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 5, and after May 17 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Apr 25. The last frost is fairly predictable here: only 23 days separate the 90% and 10% dates (median for cities on this site: 36 days).
When should I plant tomatoes in Centennial, CO?
Start seeds indoors Mar 15 – Mar 29 and set transplants outside May 17 – May 31, once nights stay above 50°F and the soil is near 60°F. That leaves 146 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 Centennial?
About 154 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 135 days, and in 1 year in 10 it runs 170 days or more. In fall there is a 10% chance of frost by Sep 25 and a 30% chance by Oct 3. That ranks 10th longest of 16 Colorado cities on this site.
When should I plant a fall garden in Centennial?
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 17. How the math works: succession and fall planting.
Did Centennial's hardiness zone change on the 2023 map?
Yes. Most of Centennial 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 Centennial compare with Aurora, CO?
Both are in zone 6a. The typical last spring frost in Centennial (May 10) comes about the same time as in Aurora, CO (May 12), 11 miles away, and the first fall frost is Oct 3 versus Oct 2. Centennial sits about 195 ft higher, which explains part of the gap. The two cities use different NOAA stations.