Flagstaff, Arizona: planting zone & frost dates
Flagstaff 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 Jun 10 and the first fall frost around Sep 23.
Frost dates
| Probability | Last spring frost (32°F) | First fall frost (32°F) |
|---|---|---|
| Safer (10% risk) | Jun 19 | Sep 16 |
| Typical planning date (30% risk) | Jun 10 | Sep 23 |
| Median (50%) | Jun 4 | Sep 28 |
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 FLAGSTAFF PULLIAM AP, AZ (USW00003103), 3.9 mi (6.2 km) from the city center and 171 ft higher than the city center (+52 m). Record used for the 1991–2020 normals: 26 years.
Why your yard may differ from the station: microclimates.
Hardiness zone across Flagstaff
Flagstaff spans more than one half-zone. Share of the city's land area by zone (via its 3 ZIP codes): 6a (54%), 6b (46%). The headline zone is the one covering the most land. Look up your ZIP for your exact zone.
Vegetable planting calendar for Flagstaff
Dates are counted from the 30%-risk frost dates above (last frost Jun 10, first frost Sep 23). Shift a week later in cold spots or low-lying ground.
| Crop | Start indoors | Transplant / plant out | Direct sow | Fall crop sow/plant |
|---|---|---|---|---|
| Tomato Short season (105 frost-free days): choose early varieties. | Apr 15 – Apr 29 | Jun 17 – Jul 1 | — | — |
| Pepper Short season (105 frost-free days): choose early varieties. | Apr 1 – Apr 15 | Jun 24 – Jul 8 | — | — |
| Lettuce | Apr 29 – May 13 | May 27 – Jun 17 | May 13 – Jun 24 | Jul 15 – Aug 12 |
| Green Beans | — | — | Jun 17 – Jul 22 | — |
| Sweet Corn Short season (105 frost-free days): choose early varieties. | — | — | Jun 17 – Jul 15 | — |
| Zucchini & Summer Squash | May 13 – May 20 | Jun 17 – Jul 1 | Jun 17 – Jul 8 | — |
| Cucumber | May 13 – May 20 | Jun 24 – Jul 1 | Jun 17 – Jul 8 | — |
| Carrot | — | — | May 20 – Jun 24 | — |
| Onion | Mar 18 – Apr 1 | May 13 – May 27 | — | — |
| Potato | — | May 13 – Jun 3 | — | — |
| Basil Short season (105 frost-free days): choose early varieties. | Apr 29 – May 13 | Jun 24 – Jul 8 | Jun 24 – Jul 15 | — |
| Spinach | — | — | Apr 29 – May 27 | Jul 29 – Aug 26 |
| Kale | Apr 15 – Apr 29 | May 13 – Jun 3 | May 13 – Jun 3 | Jul 15 – Aug 12 |
| Broccoli | Apr 15 – Apr 29 | May 27 – Jun 17 | — | — |
| Peas | — | — | Apr 29 – May 20 | Jul 15 – Jul 29 |
| Eggplant Short season (105 frost-free days): choose early varieties. | Apr 1 – Apr 15 | Jun 24 – Jul 8 | — | — |
| Cabbage | Apr 15 – Apr 29 | May 13 – May 27 | — | — |
| Radish | — | — | May 6 – Jun 24 | Aug 12 – Sep 9 |
| Strawberry | — | May 13 – Jun 3 | — | — |
| Beets | — | — | May 20 – Jul 1 | Jul 15 – Jul 29 |
Nearby cities in Arizona
- Scottsdale — zone 10a, last frost Feb 13, first frost Dec 11
- Peoria — zone 9b, last frost Feb 16, first frost Dec 2
- Phoenix — zone 9b, last frost Jan 23, first frost Dec 15
- Surprise — zone 9b, last frost Feb 16, first frost Dec 2
- Glendale — zone 9b, last frost Feb 2, first frost Dec 8
- Mesa — zone 9b, last frost Feb 12, first frost Dec 2
More: all Arizona cities · other zone 6a cities: Chicago, IL, Denver, CO, Milwaukee, WI, Colorado Springs, CO, Omaha, NE, Aurora, CO, Lincoln, NE, Fort Wayne, IN
Flagstaff gardening questions
When is the last frost in Flagstaff, AZ?
Plan around Jun 10. At NOAA's Flagstaff Pulliam Airport, AZ station, 3.9 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 Jun 4, and after Jun 19 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around May 20. The 90% and 10% dates are 29 days apart, close to the 36-day median for cities on this site.
When should I plant tomatoes in Flagstaff, AZ?
Start seeds indoors Apr 15 – Apr 29 and set transplants outside Jun 17 – Jul 1, once nights stay above 50°F and the soil is near 60°F. The 105 days between the 30% frost dates are tight for full-size tomatoes, so choose early or cherry varieties and your warmest, most sheltered spot. More: tomato planting dates by zone.
How long is the growing season in Flagstaff?
About 115 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 96 days, and in 1 year in 10 it runs 133 days or more. In fall there is a 10% chance of frost by Sep 16 and a 30% chance by Sep 23. That is the shortest of the 16 Arizona cities on this site.
When should I plant a fall garden in Flagstaff?
Count back from the first fall frost (Sep 23): sow kale Jul 15 – Aug 12; sow lettuce Jul 15 – Aug 12; sow radishes Aug 12 – Sep 9. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Oct 9. How the math works: succession and fall planting.
Did Flagstaff's hardiness zone change on the 2023 map?
No. Going by the zone that covers most of the city's land, Flagstaff is zone 6a on both the 2012 and the 2023 USDA maps (PRISM/OSU ZIP listings). About 42% of U.S. ZIP codes kept their half-zone in 2023. Why the 2023 map is warmer.
Is all of Flagstaff in zone 6a?
No. Zone 6a covers about 54% of the city's land; the rest is in 6b (46%), measured across the city's 3 ZIP codes. Check your own ZIP code in the table above or with the ZIP lookup.