Frost dates for Monmouth 4nw, IL
At Monmouth 4nw, the median last spring frost (32°F) is Apr 22 and the median first fall frost is Oct 14, for a typical growing season of 174 days. For a 90% chance that the last frost has passed, wait until May 7. Nearby ZIP codes are in USDA hardiness zone 5b.
- Apr 22Last spring frost (median)50% chance of 32°F after this date
- May 7Safer planting date10% chance of 32°F after this date
- Oct 14First fall frost (median)50% chance of 32°F by this date
- 174 daysGrowing season (median)between 32°F freezes
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 19 | May 2 | May 15 |
| 32°F | Apr 7 | Apr 22 | May 7 |
| 28°F | Mar 29 | Apr 11 | Apr 26 |
| 24°F | Mar 15 | Apr 1 | Apr 17 |
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 19 | Oct 5 | Oct 17 |
| 32°F | Sep 29 | Oct 14 | Oct 27 |
| 28°F | Oct 10 | Oct 24 | Nov 6 |
| 24°F | Oct 21 | Nov 2 | Nov 18 |
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 | 136 days | 155 days | 173 days |
| 32°F | 154 days | 174 days | 193 days |
| 28°F | 176 days | 195 days | 215 days |
| 24°F | 196 days | 215 days | 238 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 |
|---|---|---|---|
| 61447 | 5b | -15 to -10°F | 8 km |
| 61453 | 5b | -15 to -10°F | 9 km |
| 61478 | 5b | -15 to -10°F | 20 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 USC00115772, at 40.9361, -90.7197, elevation 221 m (724 ft).
- Data quality: Representative (10+ years), 24 years of freeze data.
- Average days per year at or below 32°F: 138.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Monmouth (7 km)
- Gladstone Dam 18 (26 km)
- Galesburg (28 km)
- Aledo (29 km)
- Knoxville (36 km)
- Avon (38 km)
- New Boston Dam 17 (40 km)
- Prairie City 2s (44 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.