Frost dates for 85648Rio Rico, AZ
The average last spring frost in Rio Rico is March 20 and the average first fall frost is November 17, giving a typical growing season of about 239 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Mar 20
- Average first fall frost
- Nov 17
- Growing season
- 239 days
Safer after Apr 13 (1-in-10 risk)
Possible by Oct 30 (1-in-10 risk)
First frost typically in 14 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) | Mar 24 · Apr 13 · Apr 29 | Oct 20 · Nov 5 · Nov 20 | 205 days | 100% |
| Frost / freeze (32°F) | Feb 24 · Mar 20 · Apr 13 | Oct 30 · Nov 17 · Dec 3 | 239 days | 100% |
| Hard freeze (28°F) | Jan 25 · Feb 23 · Mar 21 | Nov 11 · Nov 30 · Dec 17 | 279 days | 100% |
Planting calendar for Rio Rico
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 | Feb 17 – Apr 25 |
| Tomatoes | Transplant outdoors | Apr 5 – Jul 28 |
| Peppers | Start seeds indoors | Feb 17 – Mar 20 |
| Peppers | Transplant outdoors | Apr 19 – May 20 |
| Eggplant | Start seeds indoors | Mar 6 – Apr 4 |
| Eggplant | Transplant outdoors | Apr 19 – May 20 |
| Cucumbers | Sow outdoors | Apr 19 – Aug 7 |
| Summer squash | Sow outdoors | Apr 5 – May 20 |
| Winter squash & pumpkins | Sow outdoors | Apr 19 – May 20 |
| Snap beans | Sow outdoors | Apr 5 – Aug 30 |
| Sweet corn | Sow outdoors | Apr 5 – Jul 28 |
| Watermelon & cantaloupe | Sow outdoors | Apr 19 – May 20 |
| Okra | Sow outdoors | Apr 12 – May 5 |
| Peas | Sow outdoors (spring) | Feb 17 – Apr 4 |
| Potatoes | Plant outdoors (spring) | Feb 17 – Apr 19 |
| Onions | Start seeds indoors (spring) | Jan 6 – Feb 2 |
| Onions | Transplant outdoors (spring) | Mar 6 – Apr 4 |
| Broccoli | Start seeds indoors (spring) | Jan 30 – Mar 5 |
| Broccoli | Transplant outdoors (spring) | Mar 6 – Apr 4 |
| Broccoli | Start seeds indoors (fall) | Jul 18 – Jul 28 |
| Broccoli | Transplant outdoors (fall) | Aug 17 – Aug 28 |
| Cabbage | Start seeds indoors (spring) | Jan 20 – Feb 17 |
| Cabbage | Transplant outdoors (spring) | Feb 17 – Mar 20 |
| Cabbage | Start seeds indoors (fall) | Jul 8 – Aug 7 |
| Cabbage | Transplant outdoors (fall) | Aug 7 – Sep 7 |
| Leaf lettuce | Sow outdoors (spring) | Feb 17 – May 5 |
| Leaf lettuce | Sow outdoors (fall) | Aug 7 – Sep 23 |
| Spinach | Sow outdoors (spring) | Feb 10 – Mar 26 |
| Spinach | Sow outdoors (fall) | Aug 24 – Sep 28 |
| Radishes | Sow outdoors (spring) | Feb 17 – Apr 9 |
| Radishes | Sow outdoors (fall) | Aug 7 – Oct 8 |
| Kale | Sow outdoors (spring) | Mar 6 – Mar 26 |
| Kale | Sow outdoors (fall) | Jul 31 – Sep 7 |
| Carrots | Sow outdoors (spring) | Mar 20 – May 5 |
| Carrots | Sow outdoors (fall) | Jul 8 – Aug 23 |
| Garlic | Plant outdoors (fall) | Nov 7 – Dec 8 |
Where these dates come from
ZIP code 85648 is matched to the NOAA station Nogales Intl Ap, AZ, 23.9 km away, at 3,932 ft elevation (51 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Nogales Intl Ap, AZ (used) | 3,932 ft | Mar 20 | Nov 17 |
| Tumacacori Nm, AZ | 3,267 ft | Apr 5 | Nov 10 |
| Nogales 6 N, AZ | 3,461 ft | Apr 16 | Nov 2 |
| Santa Rita Exp Range, AZ | 4,300 ft | Feb 25 | Dec 5 |
Frost dates near Rio Rico
- Tumacacori, AZ 85640 · last Apr 5, first Nov 10
- Tubac, AZ 85646 · last Apr 5, first Nov 10
- Nogales, AZ 85628 · last Mar 20, first Nov 17
- Amado, AZ 85645 · last Apr 5, first Nov 10
- Arivaca, AZ 85601 · last Mar 21, first Nov 20
- Green Valley, AZ 85622 · last Feb 25, first Nov 27
- Patagonia, AZ 85624 · last Apr 18, first Nov 1
- Sasabe, AZ 85633 · last Mar 21, first Nov 20
Frequently asked questions
- When is the last frost in Rio Rico, AZ?
- For ZIP code 85648, the average last spring frost (32°F) is March 20, based on NOAA 1991-2020 climate normals for the Nogales Intl Ap, AZ weather station. There is a 1-in-10 chance of a frost after April 13.
- When is the first frost in Rio Rico, AZ?
- The average first fall frost (32°F) is November 17. There is a 1-in-10 chance of frost by October 30, so tender plants are at risk from that point on.
- How long is the growing season in 85648?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 239 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.