Hardiness zone 4b · 172 stations
Zone 4b Frost Dates: Typical Last Frost May 11
Summary across 172 NOAA weather stations whose location falls in zone 4b*. Dates are the typical (50% chance) frost dates of each station; the table shows the spread between stations.
- Typical last frostMay 11median station, 50% chance
- Typical first fall frostSeptember 30median station, 50% chance
- Frost-free season141 daysmedian station
- Weather stations172dates differ by weeks inside a zone
| 25% of stations | Median station | 75% of stations | |
|---|---|---|---|
| Last frost in spring (32°F) | May 6 | May 11 | May 20 |
| First frost in fall (32°F) | September 24 | September 30 | October 2 |
| Frost-free days | 127 | 141 | 148 |
Frost dates inside one zone differ by weeks: the zone describes winter cold, not the length of the season. Use the station closest to you.
Stations in zone 4b
| Station | Zone | Last spring frost (50%) | First fall frost (50%) | Frost-free days |
|---|---|---|---|---|
| Alexandria, MN | 4b | May 2 | October 8 | 159 |
| Amery, WI | 4b | May 5 | October 4 | 151 |
| Artichoke Lake 1 E, MN | 4b | May 1 | October 8 | 159 |
| Ashley, ND | 4b | May 13 | September 28 | 137 |
| Austin, MN | 4b | April 30 | October 5 | 158 |
| Baggs, WY | 4b | June 1 | September 18 | 108 |
| Basin, WY | 4b | April 28 | October 10 | 164 |
| Benson, MN | 4b | May 4 | October 3 | 151 |
| Bloomer, WI | 4b | May 5 | October 3 | 151 |
| Boulder, MT | 4b | June 7 | September 8 | 90 |
| Bowman, ND | 4b | May 16 | September 25 | 132 |
| Bozeman (Gallatin Field), MT | 4b | May 26 | September 16 | 112 |
| Brandenberg, MT | 4b | May 18 | September 22 | 126 |
| Brassua Dam, ME | 4b | May 23 | September 29 | 128 |
| Brookings, SD | 4b | May 6 | October 1 | 145 |
| Browns Valley, MN | 4b | May 9 | September 28 | 141 |
| Burris, WY | 4b | June 1 | September 14 | 104 |
| Camp Crook, SD | 4b | May 17 | September 24 | 128 |
| Canton, NY | 4b | May 9 | September 30 | 142 |
| Caribou, ME | 4b | May 7 | October 1 | 143 |
| Carlyle, MT | 4b | May 18 | September 29 | 134 |
| Cascade, MT | 4b | May 21 | September 19 | 120 |
| Choteau, MT | 4b | May 28 | September 12 | 104 |
| Clear Lake, SD | 4b | May 7 | October 1 | 146 |
| Clearmont, WY | 4b | May 24 | September 16 | 114 |
| Cochetopa Creek, CO | 4b | June 21 | September 5 | 74 |
| Columbus, MT | 4b | May 27 | September 14 | 108 |
| Corinna, ME | 4b | May 8 | October 3 | 148 |
| Cottonwood, SD | 4b | May 16 | September 26 | 132 |
| Cresco, IA | 4b | May 8 | October 1 | 147 |
| Cumberland, WI | 4b | May 5 | October 4 | 152 |
| De Smet, SD | 4b | May 5 | October 4 | 151 |
| Deaver, WY | 4b | May 6 | October 1 | 148 |
| Decorah, IA | 4b | May 3 | October 7 | 157 |
| Devils Tower #2, WY | 4b | May 23 | September 20 | 118 |
| Dillinger, WY | 4b | May 25 | September 17 | 113 |
| Dover-Foxcroft, ME | 4b | May 15 | September 28 | 134 |
| Dull Center, WY | 4b | May 15 | September 27 | 133 |
| Dupree, SD | 4b | May 8 | October 1 | 144 |
| Eau Claire, WI | 4b | May 8 | October 4 | 149 |
| Ekalaka, MT | 4b | May 20 | September 23 | 126 |
| Elkader, IA | 4b | May 8 | October 1 | 146 |
| Ellsworth, WI | 4b | May 13 | September 29 | 139 |
| Eustis, ME | 4b | May 24 | September 21 | 118 |
| Fairfield, MT | 4b | May 13 | September 27 | 135 |
| Faulkton, SD | 4b | May 10 | September 28 | 139 |
| Flandreau, SD | 4b | May 5 | October 1 | 148 |
| Flatwillow, MT | 4b | May 16 | September 28 | 132 |
| Forest Lake, MN | 4b | May 3 | October 5 | 154 |
| Forsyth, MT | 4b | May 9 | September 29 | 142 |
| Gays Mills, WI | 4b | May 3 | October 7 | 156 |
| Glad Valley, SD | 4b | May 11 | September 30 | 140 |
| Glenwood, MN | 4b | May 11 | September 27 | 139 |
| Gouverneur, NY | 4b | May 14 | September 26 | 134 |
| Grand Meadow, MN | 4b | May 6 | October 1 | 146 |
| Grand Portage, MN | 4b | May 24 | September 29 | 127 |
| Grass Range, MT | 4b | May 20 | September 24 | 126 |
| Great Falls, MT | 4b | May 19 | September 24 | 126 |
| Hardin, MT | 4b | May 13 | September 29 | 135 |
| Highmore, SD | 4b | May 12 | October 1 | 142 |
| Hill City, SD | 4b | June 1 | September 10 | 102 |
| Holter Dam, MT | 4b | May 19 | September 24 | 124 |
| Houlton, ME | 4b | May 27 | September 18 | 115 |
| Hurley, WI | 4b | May 24 | September 28 | 128 |
| Huron, SD | 4b | May 6 | October 2 | 146 |
| Hysham, MT | 4b | May 10 | September 29 | 141 |
| Idaho Falls 46 W, ID | 4b | June 11 | September 6 | 89 |
| Indian Lake 2 SW, NY | 4b | May 23 | September 27 | 125 |
| Ipswich, SD | 4b | May 8 | September 29 | 143 |
| Ironwood, MI | 4b | May 20 | October 1 | 132 |
| Jackman, ME | 4b | May 26 | September 23 | 119 |
| Jamestown, ND | 4b | May 11 | September 28 | 138 |
| Jamestown State Hosp, ND | 4b | May 8 | September 29 | 143 |
| Jeffrey City, WY | 4b | June 1 | September 13 | 104 |
| Jordan, MN | 4b | May 2 | October 5 | 153 |
| Kaycee, WY | 4b | May 18 | September 25 | 129 |
| Kennebec, SD | 4b | May 12 | September 28 | 137 |
| Lake George 8 SW, CO | 4b | June 2 | September 19 | 108 |
| Lamberton SW Research & Outreach C, MN | 4b | May 3 | October 2 | 152 |
| Laramie, WY | 4b | June 2 | September 15 | 102 |
| Lemmon, SD | 4b | May 10 | September 30 | 142 |
| Lewistown, MT | 4b | May 23 | September 21 | 119 |
| Litchfield, MN | 4b | May 6 | October 2 | 147 |
| Lowville, NY | 4b | May 8 | October 1 | 145 |
| Luck, WI | 4b | May 6 | October 4 | 149 |
| Madison, MN | 4b | May 3 | October 2 | 151 |
| Madison, SD | 4b | May 5 | September 30 | 148 |
| Malone, NY | 4b | May 6 | October 4 | 151 |
| Marshfield, WI | 4b | May 5 | October 5 | 150 |
| Massena, NY | 4b | May 8 | October 1 | 144 |
| Mather, WI | 4b | May 6 | October 3 | 148 |
| Maurine, SD | 4b | May 13 | September 28 | 136 |
| McClusky, ND | 4b | May 8 | October 1 | 145 |
| McLaughlin, SD | 4b | May 12 | September 28 | 137 |
| Medford, WI | 4b | May 11 | October 1 | 141 |
| Meeker, CO | 4b | June 4 | September 16 | 104 |
| Melstone, MT | 4b | May 10 | September 29 | 141 |
| Melville, MT | 4b | June 9 | September 7 | 88 |
| Menomonie, WI | 4b | May 9 | October 1 | 143 |
| Merrill, WI | 4b | May 11 | September 30 | 139 |
| Milan, MN | 4b | May 3 | October 2 | 151 |
| Milesville, SD | 4b | May 8 | October 2 | 147 |
| Miller, SD | 4b | May 3 | October 3 | 152 |
| Mondovi, WI | 4b | May 10 | October 2 | 144 |
| Moorhead, MT | 4b | May 17 | September 22 | 126 |
| Neillsville, WI | 4b | May 10 | October 1 | 144 |
| Newell, SD | 4b | May 8 | October 1 | 144 |
| Newport, VT | 4b | May 14 | September 30 | 138 |
| Old Fort Laramie, WY | 4b | May 14 | September 26 | 134 |
| Onida, SD | 4b | May 8 | October 2 | 147 |
| Oral, SD | 4b | May 15 | September 27 | 133 |
| Owatonna, MN | 4b | May 5 | October 6 | 154 |
| Pellston, MI | 4b | May 31 | September 18 | 108 |
| Philip, SD | 4b | May 11 | September 30 | 141 |
| Pipestone, MN | 4b | May 4 | October 2 | 152 |
| Presque Isle, ME | 4b | May 14 | September 26 | 131 |
| Preston, MN | 4b | May 14 | September 28 | 136 |
| Rangeley, ME | 4b | May 23 | September 27 | 127 |
| Rapelje, MT | 4b | May 24 | September 21 | 116 |
| Red Owl, SD | 4b | May 16 | September 26 | 131 |
| Rice Lake, WI | 4b | May 8 | October 2 | 145 |
| Richardton Abbey, ND | 4b | May 9 | October 1 | 145 |
| Ridgeland, WI | 4b | May 10 | September 29 | 140 |
| River Falls, WI | 4b | May 11 | October 1 | 143 |
| Rochester, MN | 4b | April 30 | October 6 | 159 |
| Roscoe, SD | 4b | May 7 | October 3 | 148 |
| Rosemount, MN | 4b | May 2 | October 5 | 155 |
| Rosholt, WI | 4b | May 6 | October 5 | 150 |
| Roundup, MT | 4b | May 20 | September 21 | 124 |
| Rushford, MN | 4b | May 8 | October 3 | 147 |
| Ryegate, MT | 4b | May 26 | September 18 | 112 |
| Saint Cloud, MN | 4b | May 7 | September 30 | 144 |
| Saint Johnsbury, VT | 4b | May 13 | October 3 | 143 |
| Santiago, MN | 4b | May 7 | September 28 | 144 |
| Selby, SD | 4b | May 8 | October 1 | 145 |
| Sheldon, IA | 4b | May 5 | September 28 | 145 |
| Sibley, IA | 4b | May 5 | October 3 | 152 |
| Sisseton, SD | 4b | May 4 | October 3 | 151 |
| Sonnette, MT | 4b | May 25 | September 19 | 115 |
| Sparta, WI | 4b | May 9 | October 1 | 144 |
| Stanford, MT | 4b | May 25 | September 21 | 118 |
| Theilman, MN | 4b | May 7 | October 2 | 148 |
| Timber Lake, SD | 4b | May 10 | September 30 | 141 |
| Townsend, MT | 4b | May 19 | September 19 | 122 |
| Trident, MT | 4b | May 9 | September 27 | 139 |
| Two Harbors, MN | 4b | May 12 | October 6 | 145 |
| Underwood, ND | 4b | May 10 | September 29 | 139 |
| Upton, WY | 4b | May 20 | September 23 | 123 |
| Vanderbilt, MI | 4b | June 7 | September 14 | 95 |
| Victor, SD | 4b | May 4 | October 3 | 152 |
| Watertown, SD | 4b | May 7 | September 30 | 145 |
| Waubay National Wild Life, SD | 4b | May 1 | October 12 | 164 |
| Webster, SD | 4b | May 4 | October 6 | 156 |
| Wheaton, MN | 4b | May 1 | October 9 | 160 |
| Worland (USC00489770), WY | 4b | May 4 | October 1 | 149 |
| Worland (USW00024062), WY | 4b | May 13 | September 26 | 133 |
| Wright, WY | 4b | May 25 | September 23 | 120 |
| York Pond, NH | 4b | May 23 | September 22 | 122 |
| Zumbrota, MN | 4b | May 9 | September 30 | 144 |
| near Alamosa, CO | 4b | June 7 | September 15 | 98 |
| near Collegeville, MN | 4b | May 3 | October 7 | 155 |
| near Dickinson, ND | 4b | May 18 | September 25 | 129 |
| near Kingsford, MI | 4b | May 17 | October 1 | 135 |
| near Miles City, MT | 4b | May 8 | September 30 | 144 |
| near Morris, MN | 4b | May 4 | October 1 | 150 |
| near Red Wing, MN | 4b | April 23 | October 14 | 173 |
| near Stowe, VT | 4b | May 23 | September 30 | 130 |
| near Waseca, MN | 4b | May 2 | October 4 | 155 |
Sources
- NOAA NCEI U.S. Climate Normals 1991–2020
- PRISM Group, Oregon State University — 2023 USDA Plant Hardiness Zone GIS datasets
* zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.