Frost dates for Union, MO
At Union, the median last spring frost (32°F) is Apr 11 and the median first fall frost is Oct 23, for a typical growing season of 194 days. For a 90% chance that the last frost has passed, wait until Apr 28. Nearby ZIP codes are in USDA hardiness zone 6b.
- Apr 11Last spring frost (median)50% chance of 32°F after this date
- Apr 28Safer planting date10% chance of 32°F after this date
- Oct 23First fall frost (median)50% chance of 32°F by this date
- 194 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 8 | Apr 22 | May 8 |
| 32°F | Mar 26 | Apr 11 | Apr 28 |
| 28°F | Mar 12 | Mar 31 | Apr 15 |
| 24°F | Mar 1 | Mar 18 | Apr 3 |
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 30 | Oct 13 | Oct 26 |
| 32°F | Oct 9 | Oct 23 | Nov 5 |
| 28°F | Oct 21 | Nov 3 | Nov 18 |
| 24°F | Nov 1 | Nov 14 | Dec 1 |
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 | 152 days | 172 days | 193 days |
| 32°F | 173 days | 194 days | 216 days |
| 28°F | 197 days | 217 days | 239 days |
| 24°F | 219 days | 241 days | 263 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 |
|---|---|---|---|
| 63084 | 6b | -5 to 0°F | 3 km |
| 63089 | 6b | -5 to 0°F | 11 km |
| 63077 | 6b | -5 to 0°F | 13 km |
| 63013 | 6b | -5 to 0°F | 14 km |
| 63072 | 6b | -5 to 0°F | 18 km |
| 63079 | 6b | -5 to 0°F | 21 km |
| 63015 | 6b | -5 to 0°F | 23 km |
| 63060 | 6b | -5 to 0°F | 23 km |
| 63061 | 6b | -5 to 0°F | 25 km |
| 63080 | 6b | -5 to 0°F | 26 km |
| 63041 | 6b | -5 to 0°F | 27 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 USC00238515, at 38.4444, -91.0042, elevation 165 m (540 ft).
- Data quality: Representative (10+ years), 19 years of freeze data.
- Average days per year at or below 32°F: 100.
- Frost risk changes over short distances. Valleys and low spots freeze earlier than hillsides and city centers.
Nearby weather stations
- Washington (11 km)
- Rosebud (32 km)
- St. Louis Sprt Of S L Airport (38 km)
- Weldon Spring NWS (40 km)
- Warrenton 1 N (45 km)
- St. Charles 7 SSW (50 km)
- St. Peters 2 SE (51 km)
- Festus (58 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.