Fall in zone 9bPhoto: George Chernilevsky, Public domain, via Wikimedia Commons
Frost dates for ZIP 85321 (Ajo, AZ)
Average last spring and first fall frost dates with 10%, 50% and 90% odds, from NOAA's 1991–2020 climate normals for the nearest weather station, Ajo, AZ (16 miles away).
Freezes are uncommon here
NOAA's normals for this station show a 32°F night in about 81% of years (about 2 freezing night(s) a year on average). The dates below describe freeze timing for the station's record; in many years there may be no 32°F freeze at all.
- Average last spring frostJan 1050% chance of a 32°F freeze after this date
- Average first fall frostDec 2150% chance of a 32°F freeze by this date
- Growing season (frost-free)347 daysmedian, 32°F threshold
- USDA hardiness zone9b25 to 30°F avg. coldest night
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This week in your yard
As of Oct 18, 2026, from your frost dates, zone and soil temperature. Lawn timing · Vegetables · Pruning · Plants
Freezes are uncommon here, so frost-based timing is rough. Local extension calendars for frost-free areas use months.
Soil temperature now
2-inch depth
No soil station with a fresh reading within 62 miles.
4-inch depth
No soil station with a fresh reading within 62 miles.
Fall: Texas A&M AgriLife times fall pre-emergent (for winter weeds such as annual bluegrass) to soil cooling to about 70°F for several days. The 50–55°F band is the spring trigger. Always read and follow the product label.
7-day forecast and frost risk
The latest National Weather Service 7-day forecast and any Frost Advisory or Freeze Warning for 85321 load here. You can also open the NWS forecast for this ZIP.
Pre-emergent
No soil reading near this ZIP. Typical extension timing for your region: spring late January to February; fall September to October.
Fertilizer window
Lawn region: Arid Southwest (low desert). Timing only; always follow the product label.
- Bermudagrass (warm-season): Spring: Several weeks after the lawn is fully green (April–May) (about Feb 25 here, using green-up about 3–4 weeks after your average last frost); Summer: Every 4–6 weeks through mid-August (heaviest feeder of the group); Late: Light, low-nitrogen/high-potassium feeding about 4 weeks before first frost, or skip. Avoid: Heavy late-fall nitrogen (linked to spring dead spot).
- Perennial ryegrass (cool-season): Early fall: September; Late fall: October–November; Overseeded Bermuda: Light feeding once the winter rye is established, if needed. Avoid: Summer feeding.
Plant now
- Lettuce: fall sowing Oct 12–Nov 9
- Kale: fall transplant Sep 28–Oct 26
- Collards: fall transplant Sep 28–Oct 26
- Brussels sprouts: start seeds indoors Oct 18–Nov 1
- Kohlrabi: fall sowing Oct 12–26
- Swiss chard: fall sowing Oct 12–26
- Beet: fall sowing Oct 12–26
- Turnip: fall sowing Oct 12–26
- Onion (bulbing): start seeds indoors Oct 18–Nov 1
- Green onion / scallion: fall sowing Oct 12–26
- Leek: start seeds indoors Oct 18–Nov 1
- Celery: start seeds indoors Oct 18–Nov 1
- Strawberry (plants): fall transplant Oct 12–Nov 9
Coming up in the next 3 weeks
- Pepper (sweet and hot): start seeds indoors Nov 1–15
- Eggplant: start seeds indoors Nov 1–15
- Lettuce: fall transplant Oct 26–Nov 16
- Spinach: fall sowing Oct 26–Nov 16
- Broccoli: start seeds indoors Nov 1–15
- Cabbage: start seeds indoors Nov 1–15
- Cauliflower: start seeds indoors Nov 1–15
- Bok choy / Asian greens: fall sowing Oct 26–Nov 9
- Arugula: fall sowing Oct 26–Nov 23
- Mustard greens: fall sowing Oct 26–Nov 9
- Cilantro: fall sowing Oct 26–Nov 9
- Parsley: start seeds indoors Nov 1–15
Prune now
No frost-timed pruning windows are open this week.
Spring-flowering shrubs are pruned right after their flowers fade, not by date. See the pruning guide.
Last spring frost odds
| Chance of a 32°F freeze after this date | Date |
|---|---|
| 90% (early: most years still freeze after this) | Dec 11 (prior Dec) |
| 50% (the "average" last frost) | Jan 10 |
| 10% (cautious: only 1 year in 10 freezes later) | Feb 15 |
Most gardeners plant frost-tender crops (tomatoes, peppers, basil) after the 50% date, and closer to the 10% date for less risk.
First fall frost odds
| Chance the first 32°F freeze has happened by this date | Date |
|---|---|
| 10% (early: 1 year in 10 freezes this soon) | Nov 25 |
| 50% (the "average" first frost) | Dec 21 |
| 90% (late: most years have frozen by now) | Jan 24 (next year) |
Light frost, freeze and hard freeze
| Threshold | Last spring (50%) | First fall (50%) |
|---|---|---|
| 36°F (light frost possible on clear, calm nights) | Feb 5 | Dec 8 |
| 32°F (freeze) | Jan 10 | Dec 21 |
| 28°F (hard freeze) | Jan 8 | Jan 3 (next year) |
n/a means NOAA did not publish a date at that threshold for this station (usually because it rarely gets that cold).
Vegetable planting calendar for 85321
Dates count from your average last spring frost (Jan 10) and first fall frost (Dec 21). Half of years have a frost after the spring date, so give tender crops (tomatoes, peppers, squash) some slack.
| Crop | Start indoors | Spring planting | Fall planting |
|---|---|---|---|
| Tomato | Nov 15–29 | Jan 17–31 (transplant) | Aug 24–Sep 21 (transplant) |
| Pepper (sweet and hot) | Nov 1–15 | Jan 24–Feb 7 (transplant) | Aug 31–Sep 21 (transplant) |
| Eggplant | Nov 1–15 | Jan 24–Feb 7 (transplant) | Aug 31–Sep 21 (transplant) |
| Tomatillo | Nov 15–29 | Jan 17–31 (transplant) | – |
| Lettuce | Nov 15–29 | Dec 20–Jan 10 (transplant) Dec 13–Jan 24 (sow outdoors) | Oct 26–Nov 16 (transplant) Oct 12–Nov 9 (sowing) |
| Spinach | – | Nov 29–Dec 20 (sow outdoors) | Oct 26–Nov 16 (sowing) |
| Kale | Nov 15–29 | Dec 13–27 (transplant) Dec 13–27 (sow outdoors) | Sep 28–Oct 26 (transplant) Sep 14–Oct 12 (sowing) |
| Collards | Nov 15–29 | Dec 13–Jan 10 (transplant) Dec 13–Jan 10 (sow outdoors) | Sep 28–Oct 26 (transplant) Sep 14–Oct 12 (sowing) |
| Broccoli | Nov 1–15 | Dec 13–27 (transplant) | Sep 14–Oct 12 (transplant) |
| Cabbage | Nov 1–15 | Dec 13–27 (transplant) | Sep 14–Oct 12 (transplant) |
| Cauliflower | Nov 1–15 | Dec 27–Jan 10 (transplant) | Sep 14–Oct 12 (transplant) |
| Brussels sprouts | Oct 18–Nov 1 | Dec 13–27 (transplant) | Aug 31–Sep 21 (transplant) |
| Kohlrabi | Nov 15–29 | Dec 13–27 (transplant) Dec 13–27 (sow outdoors) | Oct 12–26 (sowing) |
| Bok choy / Asian greens | – | Dec 13–27 (sow outdoors) | Oct 26–Nov 9 (sowing) |
| Arugula | – | Dec 13–Jan 10 (sow outdoors) | Oct 26–Nov 23 (sowing) |
| Mustard greens | – | Dec 13–Jan 3 (sow outdoors) | Oct 26–Nov 9 (sowing) |
| Swiss chard | Nov 29–Dec 13 | Dec 27–Jan 17 (transplant) Dec 27–Jan 24 (sow outdoors) | Oct 12–26 (sowing) |
| Beet | – | Dec 13–Jan 10 (sow outdoors) | Oct 12–26 (sowing) |
| Carrot | – | Dec 20–Jan 17 (sow outdoors) | Sep 28–Oct 12 (sowing) |
| Radish | – | Dec 6–Jan 17 (sow outdoors) | Nov 9–23 (sowing) |
| Turnip | – | Dec 13–Jan 3 (sow outdoors) | Oct 12–26 (sowing) |
| Parsnip | – | Dec 20–Jan 10 (sow outdoors) | – |
| Pea (garden, snap, snow) | – | Nov 15–Dec 13 (sow outdoors) | Sep 28–Oct 12 (sowing) |
| Onion (bulbing) | Oct 18–Nov 1 | Nov 29–Dec 13 (transplant) | – |
| Green onion / scallion | – | Nov 29–Dec 27 (sow outdoors) | Oct 12–26 (sowing) |
| Leek | Oct 18–Nov 1 | Dec 13–27 (transplant) | – |
| Garlic | – | – | Nov 9–Dec 7 (sowing) |
| Shallot | – | Nov 29–Dec 13 (transplant) | Nov 9–Dec 7 (sowing) |
| Potato | – | Dec 13–27 (transplant) | Aug 31–Sep 14 (transplant) |
| Sweet potato | – | Jan 31–Feb 14 (transplant) | – |
| Sweet corn | – | Jan 17–31 (sow outdoors) | – |
| Bean, bush (snap) | – | Jan 17–31 (sow outdoors) | Sep 28–Oct 12 (sowing) |
| Bean, pole | – | Jan 17–31 (sow outdoors) | – |
| Lima bean | – | Jan 24–Feb 7 (sow outdoors) | – |
| Southern pea (cowpea, black-eyed pea) | – | Jan 31–Feb 21 (sow outdoors) | – |
| Cucumber | Dec 13–20 | Jan 17–31 (transplant) Jan 17–31 (sow outdoors) | Sep 28–Oct 12 (sowing) |
| Summer squash / zucchini | Dec 13–20 | Jan 17–31 (transplant) Jan 17–31 (sow outdoors) | Sep 28–Oct 12 (sowing) |
| Winter squash | Dec 13–20 | Jan 17–31 (transplant) Jan 17–31 (sow outdoors) | – |
| Pumpkin | – | Jan 17–31 (sow outdoors) | – |
| Watermelon | Dec 13–20 | Jan 24–Feb 7 (transplant) Jan 24–Feb 7 (sow outdoors) | – |
| Cantaloupe / muskmelon | Dec 13–20 | Jan 24–Feb 7 (transplant) Jan 24–Feb 7 (sow outdoors) | – |
| Okra | Nov 29–Dec 13 | Jan 24–Feb 7 (transplant) Jan 24–Feb 7 (sow outdoors) | – |
| Celery | Oct 18–Nov 1 | Jan 17–24 (transplant) | – |
| Basil | Nov 29–Dec 13 | Jan 17–31 (transplant) Jan 17–31 (sow outdoors) | – |
| Cilantro | – | Dec 27–Jan 24 (sow outdoors) | Oct 26–Nov 9 (sowing) |
| Parsley | Nov 1–15 | Dec 27–Jan 10 (transplant) Dec 20–Jan 10 (sow outdoors) | – |
| Dill | – | Jan 10–24 (sow outdoors) | Oct 26–Nov 9 (sowing) |
| Sunflower | – | Jan 10–24 (sow outdoors) | – |
| Asparagus (crowns) | – | Dec 13–27 (transplant) | – |
| Rhubarb (crowns) | – | Dec 13–27 (transplant) | – |
| Strawberry (plants) | – | Dec 13–27 (transplant) | Oct 12–Nov 9 (transplant) |
Typical ranges from university extension planting calendars, adjusted to your frost dates. Probabilities, not guarantees. Fall windows that would overlap spring planting are left out, as are fall crops of frost-tender plants where the frost-free season is under 210 days.
Where these numbers come from
Station: Ajo, AZ (NOAA GHCN-Daily ID USC00020080), elevation 1,751 ft, 16.1 miles from the ZIP's center point. NOAA completeness flag: R (representative, 10+ years).
Nearby stations
| Station | Distance | Last frost (50%) | First frost (50%) |
|---|---|---|---|
| Organ Pipe Cactus Nm, AZ | 31 mi | Feb 4 | Dec 15 |
| Gila Bend 2SE, AZ | 40 mi | Jan 23 | Dec 11 |
| Painted Rock Dam, AZ | 56 mi | Jan 21 | Dec 15 |
The average last-frost dates of these stations span 25 days, a rough guide to local variation. See data sources & methods.
Frost questions for 85321
When is the last frost in 85321?
The average (50% chance) last spring freeze of 32°F for ZIP 85321 is January 10. For a more cautious planting date, use February 15, when only 1 year in 10 still sees a later freeze.
When is the first frost in 85321?
The average first fall freeze is December 21. In 1 year in 10 it comes by November 25.
What hardiness zone is 85321?
ZIP 85321 is in USDA zone 9b (25 to 30°F average coldest winter night), per the 2023 USDA Plant Hardiness Zone Map ZIP listing.
What is the soil temperature in 85321 right now?
This page shows the latest 2-inch and 4-inch soil temperature from the nearest public soil station (USDA SCAN, NOAA USCRN or TexMesonet), or a labeled estimate when no station is close, against the 50–55°F spring pre-emergent band.
Nearby ZIP codes
85341 85634 Sells 85139 Goodyear 85337 Gila Bend 85172 Stanfield 85193 Casa Grande 85138 Maricopa 85322 Arlington
Other ZIP codes in Pima County
85341 85601 85614 85619 85622 85629 85633 85634 85639 85641 85645 85653 85654 85701 85704 85705 85706 85707 85708 85709 85710 85711 85712 85713 All Pima County frost dates · Arizona frost dates
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- Freeze alerts
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Free. One weekly email plus alerts when your ZIP has a frost or a soil-temperature change worth acting on. After you submit, Kit (our email provider) sends a confirmation email: check your email and click the link to confirm. You aren't subscribed until you do. We collect only your email address and ZIP, sent to Kit to deliver The Dial. Unsubscribe anytime.