Frost dates for 86011Flagstaff, AZ
The average last spring frost in Flagstaff is June 4 and the average first fall frost is September 28, giving a typical growing season of about 115 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Jun 4
- Average first fall frost
- Sep 28
- Growing season
- 115 days
Safer after Jun 19 (1-in-10 risk)
Possible by Sep 16 (1-in-10 risk)
Last frost typically in 230 days
Frost risk by date
NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.
| Temperature | Last spring: 90% / 50% / 10% chance | First fall: 10% / 50% / 90% chance | Growing season (50%) | Years with at least one |
|---|---|---|---|---|
| Light frost (36°F) | Jun 3 · Jun 16 · Jul 1 | Sep 6 · Sep 19 · Sep 28 | 92 days | 100% |
| Frost / freeze (32°F) | May 21 · Jun 4 · Jun 19 | Sep 16 · Sep 28 · Oct 9 | 115 days | 100% |
| Hard freeze (28°F) | May 1 · May 20 · Jun 6 | Sep 28 · Oct 9 · Oct 22 | 139 days | 100% |
Planting calendar for Flagstaff
Planting windows from the University of Maryland Extension calendar, shifted to your average frost dates. Use them as a starting point and adjust for seed packet instructions and local conditions.
| Crop | Task | Window |
|---|---|---|
| Tomatoes | Start seeds indoors | May 4 – Jul 10 |
| Tomatoes | Transplant outdoors | Jun 20 – Jun 8 |
| Peppers | Start seeds indoors | May 4 – Jun 4 |
| Peppers | Transplant outdoors | Jul 4 – Aug 4 |
| Eggplant | Start seeds indoors | May 21 – Jun 19 |
| Eggplant | Transplant outdoors | Jul 4 – Aug 4 |
| Cucumbers | Sow outdoors | Jul 4 – Jun 18 |
| Summer squash | Sow outdoors | Jun 20 – Aug 4 |
| Winter squash & pumpkins | Sow outdoors | Jul 4 – Aug 4 |
| Snap beans | Sow outdoors | Jun 20 – Jul 11 |
| Sweet corn | Sow outdoors | Jun 20 – Jun 8 |
| Watermelon & cantaloupe | Sow outdoors | Jul 4 – Aug 4 |
| Okra | Sow outdoors | Jun 27 – Jul 20 |
| Peas | Sow outdoors (spring) | May 4 – Jun 19 |
| Potatoes | Plant outdoors (spring) | May 4 – Jul 4 |
| Onions | Start seeds indoors (spring) | Mar 23 – Apr 19 |
| Onions | Transplant outdoors (spring) | May 21 – Jun 19 |
| Broccoli | Start seeds indoors (spring) | Apr 16 – May 20 |
| Broccoli | Transplant outdoors (spring) | May 21 – Jun 19 |
| Broccoli | Start seeds indoors (fall) | May 29 – Jun 8 |
| Broccoli | Transplant outdoors (fall) | Jun 28 – Jul 9 |
| Cabbage | Start seeds indoors (spring) | Apr 6 – May 4 |
| Cabbage | Transplant outdoors (spring) | May 4 – Jun 4 |
| Cabbage | Start seeds indoors (fall) | May 19 – Jun 18 |
| Cabbage | Transplant outdoors (fall) | Jun 18 – Jul 19 |
| Leaf lettuce | Sow outdoors (spring) | May 4 – Jul 20 |
| Leaf lettuce | Sow outdoors (fall) | Jun 18 – Aug 4 |
| Spinach | Sow outdoors (spring) | Apr 27 – Jun 10 |
| Spinach | Sow outdoors (fall) | Jul 5 – Aug 9 |
| Radishes | Sow outdoors (spring) | May 4 – Jun 24 |
| Radishes | Sow outdoors (fall) | Jun 18 – Aug 19 |
| Kale | Sow outdoors (spring) | May 21 – Jun 10 |
| Kale | Sow outdoors (fall) | Jun 11 – Jul 19 |
| Carrots | Sow outdoors (spring) | Jun 4 – Jul 20 |
| Carrots | Sow outdoors (fall) | May 19 – Jul 4 |
| Garlic | Plant outdoors (fall) | Sep 18 – Oct 19 |
Where these dates come from
ZIP code 86011 is matched to the NOAA station Flagstaff Pulliam Ap, AZ, 6.1 km away, at 7,003 ft elevation (103 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Flagstaff Pulliam Ap, AZ (used) | 7,003 ft | Jun 4 | Sep 28 |
| Flagstaff 4 Sw, AZ | 7,125 ft | Jun 23 | Sep 15 |
| Ft Valley, AZ | 7,347 ft | Jun 11 | Sep 25 |
| Walnut Canyon Nm, AZ | 6,695 ft | May 13 | Oct 6 |
Frost dates near Flagstaff
- Flagstaff, AZ 86002 · last Jun 4, first Sep 28
- Bellemont, AZ 86015 · last Jun 21, first Sep 17
- Parks, AZ 86018 · last Jun 21, first Sep 17
- Munds Park, AZ 86017 · last Jun 10, first Sep 27
- Mormon Lake, AZ 86038 · last Jun 1, first Oct 3
- Sedona, AZ 86339 · last Apr 1, first Nov 17
- Cornville, AZ 86325 · last Mar 30, first Nov 10
- Clarkdale, AZ 86324 · last Mar 30, first Nov 10
Frequently asked questions
- When is the last frost in Flagstaff, AZ?
- For ZIP code 86011, the average last spring frost (32°F) is June 4, based on NOAA 1991-2020 climate normals for the Flagstaff Pulliam Ap, AZ weather station. There is a 1-in-10 chance of a frost after June 19.
- When is the first frost in Flagstaff, AZ?
- The average first fall frost (32°F) is September 28. There is a 1-in-10 chance of frost by September 16, so tender plants are at risk from that point on.
- How long is the growing season in 86011?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 115 days long.
- Are these frost dates a forecast?
- No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.