Frost dates for 62521Decatur, IL
The average last spring frost in Decatur is April 14 and the average first fall frost is October 24, giving a typical growing season of about 192 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 14
- Average first fall frost
- Oct 24
- Growing season
- 192 days
Safer after May 1 (1-in-10 risk)
Possible by Oct 11 (1-in-10 risk)
Last frost typically in 166 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) | Apr 12 · Apr 26 · May 13 | Sep 30 · Oct 14 · Oct 27 | 170 days | 100% |
| Frost / freeze (32°F) | Apr 1 · Apr 14 · May 1 | Oct 11 · Oct 24 · Nov 5 | 192 days | 100% |
| Hard freeze (28°F) | Mar 18 · Apr 3 · Apr 17 | Oct 20 · Nov 3 · Nov 19 | 214 days | 100% |
Planting calendar for Decatur
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 14 – May 20 |
| Tomatoes | Transplant outdoors | Apr 30 – Jul 4 |
| Peppers | Start seeds indoors | Mar 14 – Apr 14 |
| Peppers | Transplant outdoors | May 14 – Jun 14 |
| Eggplant | Start seeds indoors | Mar 31 – Apr 29 |
| Eggplant | Transplant outdoors | May 14 – Jun 14 |
| Cucumbers | Sow outdoors | May 14 – Jul 14 |
| Summer squash | Sow outdoors | Apr 30 – Jun 14 |
| Winter squash & pumpkins | Sow outdoors | May 14 – Jun 14 |
| Snap beans | Sow outdoors | Apr 30 – Aug 6 |
| Sweet corn | Sow outdoors | Apr 30 – Jul 4 |
| Watermelon & cantaloupe | Sow outdoors | May 14 – Jun 14 |
| Okra | Sow outdoors | May 7 – May 30 |
| Peas | Sow outdoors (spring) | Mar 14 – Apr 29 |
| Potatoes | Plant outdoors (spring) | Mar 14 – May 14 |
| Onions | Start seeds indoors (spring) | Jan 31 – Feb 27 |
| Onions | Transplant outdoors (spring) | Mar 31 – Apr 29 |
| Broccoli | Start seeds indoors (spring) | Feb 24 – Mar 30 |
| Broccoli | Transplant outdoors (spring) | Mar 31 – Apr 29 |
| Broccoli | Start seeds indoors (fall) | Jun 24 – Jul 4 |
| Broccoli | Transplant outdoors (fall) | Jul 24 – Aug 4 |
| Cabbage | Start seeds indoors (spring) | Feb 14 – Mar 14 |
| Cabbage | Transplant outdoors (spring) | Mar 14 – Apr 14 |
| Cabbage | Start seeds indoors (fall) | Jun 14 – Jul 14 |
| Cabbage | Transplant outdoors (fall) | Jul 14 – Aug 14 |
| Leaf lettuce | Sow outdoors (spring) | Mar 14 – May 30 |
| Leaf lettuce | Sow outdoors (fall) | Jul 14 – Aug 30 |
| Spinach | Sow outdoors (spring) | Mar 7 – Apr 20 |
| Spinach | Sow outdoors (fall) | Jul 31 – Sep 4 |
| Radishes | Sow outdoors (spring) | Mar 14 – May 4 |
| Radishes | Sow outdoors (fall) | Jul 14 – Sep 14 |
| Kale | Sow outdoors (spring) | Mar 31 – Apr 20 |
| Kale | Sow outdoors (fall) | Jul 7 – Aug 14 |
| Carrots | Sow outdoors (spring) | Apr 14 – May 30 |
| Carrots | Sow outdoors (fall) | Jun 14 – Jul 30 |
| Garlic | Plant outdoors (fall) | Oct 14 – Nov 14 |
Where these dates come from
ZIP code 62521 is matched to the NOAA station Decatur Wtp, IL, 1.2 km away, at 639 ft elevation (37 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Decatur Wtp, IL (used) | 639 ft | Apr 14 | Oct 24 |
| Decatur Ap, IL | 675 ft | Apr 16 | Oct 22 |
| Sullivan 3S, IL | 640 ft | Apr 15 | Oct 22 |
| Lincoln, IL | 583 ft | Apr 20 | Oct 16 |
Frost dates near Decatur
- Decatur, IL 62523 · last Apr 14, first Oct 24
- Elwin, IL 62532 · last Apr 14, first Oct 24
- Forsyth, IL 62535 · last Apr 14, first Oct 24
- Mt Zion, IL 62549 · last Apr 16, first Oct 22
- Harristown, IL 62537 · last Apr 14, first Oct 24
- Boody, IL 62514 · last Apr 14, first Oct 24
- Oreana, IL 62554 · last Apr 16, first Oct 22
- Macon, IL 62544 · last Apr 14, first Oct 24
Frequently asked questions
- When is the last frost in Decatur, IL?
- For ZIP code 62521, the average last spring frost (32°F) is April 14, based on NOAA 1991-2020 climate normals for the Decatur Wtp, IL weather station. There is a 1-in-10 chance of a frost after May 1.
- When is the first frost in Decatur, IL?
- The average first fall frost (32°F) is October 24. There is a 1-in-10 chance of frost by October 11, so tender plants are at risk from that point on.
- How long is the growing season in 62521?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 192 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.