Frost dates for La Harpe, IL
At La Harpe, the median last spring frost (32°F) is Apr 21 and the median first fall frost is Oct 19, for a typical growing season of 180 days. For a 90% chance that the last frost has passed, wait until May 5. Nearby ZIP codes are in USDA hardiness zones 5b to 6a.
- Apr 21Last spring frost (median)50% chance of 32°F after this date
- May 5Safer planting date10% chance of 32°F after this date
- Oct 19First fall frost (median)50% chance of 32°F by this date
- 180 daysGrowing season (median)between 32°F freezes
USDA hardiness zone 6a (-10 to -5°F) · see all zone 6a frost dates
Last spring frost dates
The chance that the temperature drops to the threshold after each date.
| Temperature | 90% chance later | 50% chance later | 10% chance later |
|---|---|---|---|
| 36°F | Apr 17 | May 1 | May 15 |
| 32°F | Apr 6 | Apr 21 | May 5 |
| 28°F | Mar 25 | Apr 8 | Apr 25 |
| 24°F | Mar 11 | Mar 30 | Apr 14 |
First fall frost dates
The chance that the temperature has dropped to the threshold by each date.
| Temperature | 10% chance by | 50% chance by | 90% chance by |
|---|---|---|---|
| 36°F | Sep 24 | Oct 8 | Oct 21 |
| 32°F | Oct 4 | Oct 19 | Oct 31 |
| 28°F | Oct 16 | Oct 28 | Nov 10 |
| 24°F | Oct 27 | Nov 7 | Nov 20 |
Growing season length
Days between the last spring and first fall freeze, as the length reached in 9, 5 and 1 out of 10 years.
| Temperature | 9 in 10 years at least | 5 in 10 years at least | 1 in 10 years at least |
|---|---|---|---|
| 36°F | 138 days | 159 days | 178 days |
| 32°F | 161 days | 180 days | 199 days |
| 28°F | 180 days | 201 days | 221 days |
| 24°F | 201 days | 222 days | 244 days |
Chance of a freeze in any year
| Temperature | Chance per year |
|---|---|
| 36°F | 100% |
| 32°F | 100% |
| 28°F | 100% |
| 24°F | 100% |
ZIP codes whose closest station is this one
| ZIP | Hardiness zone | Avg. extreme low | Distance |
|---|---|---|---|
| 61450 | 6a | -10 to -5°F | 2 km |
| 61420 | 6a | -10 to -5°F | 9 km |
| 62330 | 6a | -10 to -5°F | 13 km |
| 61480 | 6a | -10 to -5°F | 17 km |
| 61475 | 5b | -15 to -10°F | 18 km |
| 61460 | 5b | -15 to -10°F | 19 km |
| 62326 | 6a | -10 to -5°F | 22 km |
Not the official USDA Plant Hardiness Zone Map. Zones shown here are the values published in the USDA-ARS / Oregon State University PRISM Group 2023 ZIP code tables, shown unaltered. For the official interactive map, visit planthardiness.ars.usda.gov.
About this station
- NOAA station ID USC00114823, at 40.5839, -90.9686, elevation 210 m (690 ft).
- Data quality: Representative (10+ years), 24 years of freeze data.
- Average days per year at or below 32°F: 134.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Bentley (29 km)
- Gladstone Dam 18 (33 km)
- Prairie City 2S (43 km)
- Monmouth 4NW (44 km)
- Avon (45 km)
- Monmouth (49 km)
- Golden (53 km)
- Rushville (61 km)
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020, annual/seasonal normals by station (version 1.0.1), file dated June 27, 2023; documentation.
- USDA Agricultural Research Service and PRISM Group, Oregon State University, 2023 Plant Hardiness Zone Map ZIP code tables (CONUS, Alaska, Hawaii, Puerto Rico), files dated November 17, 2023. Data © PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed November 1, 2026. Official map: planthardiness.ars.usda.gov.
- U.S. Census Bureau, 2024 Gazetteer ZIP Code Tabulation Areas file, dated August 30, 2024 (ZIP centroids used to find the nearest station).
Freeze dates are 30-year probabilities, not forecasts. Check your local forecast before planting tender plants.