Frost dates for 62002Alton, IL
The average last spring frost in Alton is April 4 and the average first fall frost is November 5, giving a typical growing season of about 214 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 4
- Average first fall frost
- Nov 5
- Growing season
- 214 days
Safer after Apr 19 (1-in-10 risk)
Possible by Oct 25 (1-in-10 risk)
First frost typically in 7 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 31 · Apr 14 · May 1 | Oct 12 · Oct 27 · Nov 8 | 192 days | 100% |
| Frost / freeze (32°F) | Mar 18 · Apr 4 · Apr 19 | Oct 25 · Nov 5 · Nov 21 | 214 days | 100% |
| Hard freeze (28°F) | Mar 6 · Mar 25 · Apr 9 | Nov 2 · Nov 16 · Dec 1 | 237 days | 100% |
Planting calendar for Alton
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 | Mar 4 – May 10 |
| Tomatoes | Transplant outdoors | Apr 20 – Jul 16 |
| Peppers | Start seeds indoors | Mar 4 – Apr 4 |
| Peppers | Transplant outdoors | May 4 – Jun 4 |
| Eggplant | Start seeds indoors | Mar 21 – Apr 19 |
| Eggplant | Transplant outdoors | May 4 – Jun 4 |
| Cucumbers | Sow outdoors | May 4 – Jul 26 |
| Summer squash | Sow outdoors | Apr 20 – Jun 4 |
| Winter squash & pumpkins | Sow outdoors | May 4 – Jun 4 |
| Snap beans | Sow outdoors | Apr 20 – Aug 18 |
| Sweet corn | Sow outdoors | Apr 20 – Jul 16 |
| Watermelon & cantaloupe | Sow outdoors | May 4 – Jun 4 |
| Okra | Sow outdoors | Apr 27 – May 20 |
| Peas | Sow outdoors (spring) | Mar 4 – Apr 19 |
| Potatoes | Plant outdoors (spring) | Mar 4 – May 4 |
| Onions | Start seeds indoors (spring) | Jan 21 – Feb 17 |
| Onions | Transplant outdoors (spring) | Mar 21 – Apr 19 |
| Broccoli | Start seeds indoors (spring) | Feb 14 – Mar 20 |
| Broccoli | Transplant outdoors (spring) | Mar 21 – Apr 19 |
| Broccoli | Start seeds indoors (fall) | Jul 6 – Jul 16 |
| Broccoli | Transplant outdoors (fall) | Aug 5 – Aug 16 |
| Cabbage | Start seeds indoors (spring) | Feb 4 – Mar 4 |
| Cabbage | Transplant outdoors (spring) | Mar 4 – Apr 4 |
| Cabbage | Start seeds indoors (fall) | Jun 26 – Jul 26 |
| Cabbage | Transplant outdoors (fall) | Jul 26 – Aug 26 |
| Leaf lettuce | Sow outdoors (spring) | Mar 4 – May 20 |
| Leaf lettuce | Sow outdoors (fall) | Jul 26 – Sep 11 |
| Spinach | Sow outdoors (spring) | Feb 25 – Apr 10 |
| Spinach | Sow outdoors (fall) | Aug 12 – Sep 16 |
| Radishes | Sow outdoors (spring) | Mar 4 – Apr 24 |
| Radishes | Sow outdoors (fall) | Jul 26 – Sep 26 |
| Kale | Sow outdoors (spring) | Mar 21 – Apr 10 |
| Kale | Sow outdoors (fall) | Jul 19 – Aug 26 |
| Carrots | Sow outdoors (spring) | Apr 4 – May 20 |
| Carrots | Sow outdoors (fall) | Jun 26 – Aug 11 |
| Garlic | Plant outdoors (fall) | Oct 26 – Nov 26 |
Where these dates come from
ZIP code 62002 is matched to the NOAA station Alton - Melvin Price L&D, IL, 4.7 km away, at 405 ft elevation (91 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Alton - Melvin Price L&D, IL (used) | 405 ft | Apr 4 | Nov 5 |
| St Charles Co Ap, MO | 436 ft | Apr 5 | Oct 27 |
| St Louis Lambert Intl Ap, MO | 531 ft | Apr 2 | Nov 4 |
| Jerseyville 2 Sw, IL | 630 ft | Apr 14 | Oct 19 |
Frost dates near Alton
- Godfrey, IL 62035 · last Apr 4, first Nov 5
- Cottage Hills, IL 62018 · last Apr 4, first Nov 5
- East Alton, IL 62024 · last Apr 4, first Nov 5
- Wood River, IL 62095 · last Apr 4, first Nov 5
- West Alton, MO 63386 · last Apr 4, first Nov 5
- Roxana, IL 62084 · last Apr 4, first Nov 5
- Hartford, IL 62048 · last Apr 4, first Nov 5
- Bethalto, IL 62010 · last Apr 4, first Nov 5
Frequently asked questions
- When is the last frost in Alton, IL?
- For ZIP code 62002, the average last spring frost (32°F) is April 4, based on NOAA 1991-2020 climate normals for the Alton - Melvin Price L&D, IL weather station. There is a 1-in-10 chance of a frost after April 19.
- When is the first frost in Alton, IL?
- The average first fall frost (32°F) is November 5. There is a 1-in-10 chance of frost by October 25, so tender plants are at risk from that point on.
- How long is the growing season in 62002?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 214 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.