Frost dates for Knoxville, IL
At Knoxville, the median last spring frost (32°F) is Apr 21 and the median first fall frost is Oct 20, for a typical growing season of 181 days. For a 90% chance that the last frost has passed, wait until May 6. Nearby ZIP codes are in USDA hardiness zone 5b.
- Apr 21Last spring frost (median)50% chance of 32°F after this date
- May 6Safer planting date10% chance of 32°F after this date
- Oct 20First fall frost (median)50% chance of 32°F by this date
- 181 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 17 | Apr 30 | May 15 |
| 32°F | Apr 7 | Apr 21 | May 6 |
| 28°F | Mar 26 | Apr 9 | Apr 24 |
| 24°F | Mar 12 | Mar 31 | Apr 11 |
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 29 | Oct 11 | Oct 22 |
| 32°F | Oct 7 | Oct 20 | Oct 31 |
| 28°F | Oct 17 | Oct 29 | Nov 10 |
| 24°F | Oct 28 | Nov 7 | Nov 23 |
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 | 143 days | 161 days | 179 days |
| 32°F | 161 days | 181 days | 199 days |
| 28°F | 182 days | 202 days | 220 days |
| 24°F | 205 days | 223 days | 245 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 |
|---|---|---|---|
| 61430 | 5b | -15 to -10°F | 5 km |
| 61448 | 5b | -15 to -10°F | 5 km |
| 61436 | 5b | -15 to -10°F | 7 km |
| 61428 | 5b | -15 to -10°F | 15 km |
| 61458 | 5b | -15 to -10°F | 16 km |
| 61489 | 5b | -15 to -10°F | 22 km |
| 61572 | 5b | -15 to -10°F | 24 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 USC00114780, at 40.9025, -90.2897, elevation 222 m (728 ft).
- Data quality: Representative (10+ years), 15 years of freeze data.
- Average days per year at or below 32°F: 135.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Galesburg (9 km)
- Altona (26 km)
- Avon (30 km)
- Monmouth (30 km)
- Monmouth 4nw (36 km)
- Galva (37 km)
- Prairie City 2s (38 km)
- Princeville (45 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.