Flagstaff, AZ planting zone & frost dates
Flagstaff is in USDA hardiness zone 6a. The last spring frost usually comes around June 4 and the first fall frost around September 28, for a growing season of about 115 days.
Planting calendar for Flagstaff
Dates are counted from the average last spring frost (June 4) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.
| Crop | When |
|---|---|
| Tomatoes | Start seeds indoors: Apr 9 – Apr 23 Transplant outdoors: Jun 11 – Jun 18 |
| Peppers | Start seeds indoors: Mar 26 – Apr 9 Transplant outdoors: Jun 18 – Jun 25 |
| Eggplant | Start seeds indoors: Mar 26 – Apr 9 Transplant outdoors: Jun 18 – Jun 25 |
| Broccoli | Start seeds indoors: Mar 26 – Apr 9 Transplant outdoors: May 7 – May 21 |
| Cabbage | Start seeds indoors: Mar 26 – Apr 9 Transplant outdoors: May 7 – May 21 |
| Onions (sets) | Plant outdoors: May 7 – May 21 |
| Peas | Sow outdoors: Apr 23 – May 7 |
| Spinach | Sow outdoors: Apr 23 – May 7 |
| Lettuce | Sow outdoors: May 7 – May 21 |
| Carrots | Sow outdoors: May 7 – May 21 |
| Potatoes | Plant outdoors: May 7 – May 21 |
| Beans | Sow outdoors: Jun 11 – Jun 18 |
| Sweet corn | Sow outdoors: Jun 11 – Jun 18 |
| Cucumbers | Sow outdoors: Jun 11 – Jun 18 |
| Squash & zucchini | Sow outdoors: Jun 11 – Jun 18 |
| Basil | Start seeds indoors: Apr 23 – May 7 Transplant outdoors: Jun 11 – Jun 18 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 3 (8 weeks before the average first fall frost on Sep 28).
Useful for zone 6a gardens
- Seed starting kit with dome — to start seeds indoors before the last frost
- LED grow light for seedlings — stops leggy seedlings
- Frost cloth / plant covers — for late spring and early fall frosts
- Soil thermometer — warm-season crops need soil above 60°F
- Cold frame / mini greenhouse — adds weeks to a short season
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Frost risk in detail
| 90% chance | 50% chance | 10% chance | |
|---|---|---|---|
| Last 32°F frost in spring is after | May 21 | Jun 4 | Jun 19 |
| First 32°F frost in fall is before | Oct 9 | Sep 28 | Sep 16 |
How to read it: in spring there is a 10% chance of a frost after June 19, so that is a safe date for tender plants. In fall there is a 10% chance of frost before September 16. A hard freeze (28°F) usually ends around May 20.
Hardiness zone by ZIP code in Flagstaff
- 86001 zone 6a
- 86002 zone 6a
- 86003 zone 7a
- 86004 zone 6b
- 86005 zone 6a
Nearby cities
- Sedona zone 8b, last frost Apr 1
- West Sedona zone 8b, last frost Apr 1
- Cottonwood zone 8b, last frost Mar 30
- Verde Village zone 8b, last frost Mar 30
- Camp Verde zone 8a, last frost Apr 16
- Prescott Valley zone 7b, last frost Apr 20
- Chino Valley zone 8a, last frost Apr 27
- Payson zone 8b, last frost Apr 29
Questions
What growing zone is Flagstaff, AZ?
Flagstaff is in USDA Plant Hardiness Zone 6a (average extreme winter low -10°F to -5°F), according to the USDA 2023 map. Some ZIP codes of the city fall in zones 6b, 7a.
When is the last frost in Flagstaff?
The average last spring frost (32°F) in Flagstaff is June 4. There is still a 10% chance of frost until June 19.
When can I plant tomatoes in Flagstaff?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around Jun 11 – Jun 18. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Flagstaff Pulliam Ap, AZ (USW00003103), 6.1 km (3.8 mi) from the city center, elevation 2134 m, based on 26 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.