Aurora, Colorado: planting zone & frost dates
Aurora 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 12 and the first fall frost around Oct 2.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | May 21 | Sep 25 |
| Typical planning date (30% risk) | May 12 | Oct 2 |
| Median (50%) | May 7 | 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 CHERRY CREEK DAM, CO (USC00051547), 8.3 mi (13.3 km) from the city center and 102 ft higher than the city center (+31 m). Record used for the 1991–2020 normals: 13 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Aurora
All 13 ZIP codes covering Aurora are in zone 6a.
Vegetable planting calendar for Aurora
Dates are counted from the 30%-risk frost dates above (last frost May 12, first frost Oct 2). 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 17 – Mar 31 | May 19 – Jun 2 | — | — |
| Pepper | Mar 3 – Mar 17 | May 26 – Jun 9 | — | — |
| Lettuce | Mar 31 – Apr 14 | Apr 28 – May 19 | Apr 14 – May 26 | Jul 24 – Aug 21 |
| Green Beans | — | — | May 19 – Jun 23 | Jul 10 – Jul 24 |
| Sweet Corn | — | — | May 19 – Jun 16 | — |
| Zucchini & Summer Squash | Apr 14 – Apr 21 | May 19 – Jun 2 | May 19 – Jun 9 | Jul 10 – Jul 24 |
| Cucumber | Apr 14 – Apr 21 | May 26 – Jun 2 | May 19 – Jun 9 | Jul 10 – Jul 24 |
| Carrot | — | — | Apr 21 – May 26 | Jul 10 – Jul 24 |
| Onion | Feb 17 – Mar 3 | Apr 14 – Apr 28 | — | — |
| Potato | — | Apr 14 – May 5 | — | — |
| Basil | Mar 31 – Apr 14 | May 26 – Jun 9 | May 26 – Jun 16 | — |
| Spinach | — | — | Mar 31 – Apr 28 | Aug 7 – Sep 4 |
| Kale | Mar 17 – Mar 31 | Apr 14 – May 5 | Apr 14 – May 5 | Jul 24 – Aug 21 |
| Broccoli | Mar 17 – Mar 31 | Apr 28 – May 19 | — | Jul 10 – Jul 24 |
| Peas | — | — | Mar 31 – Apr 21 | Jul 24 – Aug 7 |
| Eggplant | Mar 3 – Mar 17 | May 26 – Jun 9 | — | — |
| Cabbage | Mar 17 – Mar 31 | Apr 14 – Apr 28 | — | Jul 10 – Jul 24 |
| Radish | — | — | Apr 7 – May 26 | Aug 21 – Sep 18 |
| Strawberry | — | Apr 14 – May 5 | — | — |
| Beets | — | — | Apr 21 – Jun 2 | Jul 24 – Aug 7 |
Nearby cities in Colorado
- Denver — zone 6a, last frost May 8, first frost Oct 3
- Centennial — zone 6a, last frost May 10, first frost Oct 3
- Thornton — zone 6a, last frost May 7, first frost Oct 4
- Castle Rock — zone 5b, last frost May 15, first frost Sep 27
- Westminster — zone 6a, last frost May 7, first frost Oct 4
- Lakewood — zone 6a, last frost May 8, first frost Oct 2
More: all Colorado cities · other zone 6a cities: Chicago, IL, Denver, CO, Milwaukee, WI, Colorado Springs, CO, Omaha, NE, Lincoln, NE, Fort Wayne, IN, Worcester, MA
Aurora gardening questions
When is the last frost in Aurora, CO?
Plan around May 12. At NOAA's Cherry Creek Dam, CO station, 8.3 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 7, and after May 21 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Apr 29. The last frost is fairly predictable here: only 25 days separate the 90% and 10% dates (median for cities on this site: 36 days).
When should I plant tomatoes in Aurora, CO?
Start seeds indoors Mar 17 – Mar 31 and set transplants outside May 19 – Jun 2, once nights stay above 50°F and the soil is near 60°F. That leaves 143 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 Aurora?
About 152 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 133 days, and in 1 year in 10 it runs 169 days or more. In fall there is a 10% chance of frost by Sep 25 and a 30% chance by Oct 2. That ranks 11th longest of 16 Colorado cities on this site.
When should I plant a fall garden in Aurora?
Count back from the first fall frost (Oct 2): transplant broccoli Jul 10 – Jul 24; sow kale Jul 24 – Aug 21; sow lettuce Jul 24 – Aug 21; sow radishes Aug 21 – Sep 18. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Oct 15. How the math works: succession and fall planting.
Did Aurora's hardiness zone change on the 2023 map?
Yes. Most of Aurora 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 Aurora compare with Denver, CO?
Both are in zone 6a. The typical last spring frost in Aurora (May 12) comes about 4 days later than in Denver, CO (May 8), 9 miles away, and the first fall frost is Oct 2 versus Oct 3. Aurora sits about 252 ft higher, which explains part of the gap. The two cities use different NOAA stations.