USDA zone 5a in Iowa
USDA plant hardiness zone 5a covers 89 locations across Iowa (average annual extreme minimum −20 to −15 °F): Algona, IA, Allison, IA, Armstrong, IA, Asbury, IA, Atlantic, IA, Audubon, IA, and 83 more. Average last spring frost across this group ranges April 13 (Sabula) to May 8 (St. Olaf), and growing seasons run 145–195 days (Sheldon to Sabula) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Iowa location's own frost dates; the printable planting calendar uses Clarion, this group's median-season location.
- USDA zone
- 5a−20 to −15 °F
- Last frost range
- Apr 13–May 8avg, 32°F
- First frost range
- Sep 28–Oct 26avg, 32°F
- Growing season range
- 145–195days
Locations in this group
Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.
| Location | Also covers | Nearest station | Last frost | First frost | Season (days) |
|---|---|---|---|---|---|
| Algona | Lu Verne, Renwick, West Bend, St. Joseph, Wesley, Livermore, +6 more | Algona | Apr 30 | Oct 6 | 160 |
| Allison | Dumont, Shell Rock, Parkersburg, Clarksville, Greene, Bristow, +1 more | Allison | Apr 27 | Oct 8 | 165 |
| Armstrong | Elmore, Swea, Lakota, Bancroft, Ledyard | Swea City 5n | May 4 | Oct 1 | 150 |
| Asbury | Menominee, Hazel Green, Cuba, Dickeyville, Rickardsville, Benton, +3 more | Dubuque L&d 11 | Apr 19 | Oct 21 | 184 |
| Atlantic | Walnut, Brayton | Atlantic 1 Ne | Apr 30 | Oct 2 | 153 |
| Audubon | Coon Rapids, Gray, Exira, Elk Horn, Irwin, Kirkman | Audubon | May 2 | Oct 3 | 154 |
| Belle Plaine | Brooklyn, Chelsea, Elberon, Vining, Blairstown, Victor, +3 more | Belle Plaine | Apr 28 | Oct 10 | 165 |
| Bellevue | Miles, Spragueville, Springbrook | Bellevue L&d 12 | Apr 25 | Oct 16 | 172 |
| Belmond | Garner, Kanawha, Meservey, Corwith, Britt, Klemme, +3 more | Britt 3e | Apr 29 | Oct 7 | 161 |
| Bevington | — | Indianola 2w | Apr 24 | Oct 12 | 168 |
| Blencoe | Little Sioux | Little Sioux 2 Nw | May 1 | Oct 3 | 155 |
| Boone | Ogden, Boxholm, Pilot Mound, Dayton, Beaver | Boone | Apr 28 | Oct 12 | 165 |
| Carroll | Manning, Lidderdale, Ralston, Glidden, Arcadia, Lanesboro, +4 more | Carroll | Apr 27 | Oct 10 | 166 |
| Cedar Rapids | Fairfax, Ely, Atkins, Walford, Swisher, Norway, +1 more | Cedar Rapids Muni Ap | Apr 27 | Oct 11 | 165 |
| Charles | Nashua, Marble Rock, Rockford, Floyd, Colwell | Charles City | Apr 30 | Oct 6 | 157 |
| Cherokee | Marcus, Aurelia, Washta, Peterson, Pierson, Quimby, +3 more | Cherokee | May 4 | Oct 4 | 152 |
| Churdan | Scranton, Harcourt, Grand Junction, Paton, Bagley, Dana | Jefferson | Apr 26 | Oct 9 | 164 |
| Clarion * | — | Clarion | Apr 30 | Oct 10 | 162 |
| Clear Lake | Ventura, Thornton, Hanlontown, Swaledale | Mason City Muni Ap | May 3 | Oct 1 | 150 |
| Coggon | — | Coggon | May 3 | Oct 7 | 156 |
| Colo | State Center, Zearing, McCallsburg | Colo | Apr 24 | Oct 12 | 170 |
| Conrad | Liscomb, St. Anthony, Albion, Clemons, Beaman | Marshalltown Muni Ap | Apr 30 | Oct 6 | 159 |
| Decorah | Ossian, Spillville, Fort Atkinson | Decorah | May 3 | Oct 7 | 157 |
| Denison | Westside, Schleswig, Manilla, Vail, Deloit, Defiance, +3 more | Denison | Apr 27 | Oct 11 | 166 |
| Dolliver | Dunnell | Estherville Muni Ap | May 2 | Sep 30 | 150 |
| Dyersville | Monticello, Cascade, Epworth, Farley, Center Junction, Hopkinton, +4 more | Cascade | Apr 28 | Oct 10 | 164 |
| Eldora | Hubbard, New Providence, Garden, Union, Steamboat Rock, Whitten | Eldora | Apr 27 | Oct 10 | 165 |
| Emmetsburg | Graettinger, Curlew, Ruthven, Mallard, Ayrshire, Cylinder | Emmetsburg | Apr 27 | Oct 7 | 164 |
| Estherville | Ringsted, Wallingford | Estherville 4e | May 2 | Oct 3 | 153 |
| Forest | Lake Mills, Leland, Buffalo Center, Joice, Fertile, Thompson, +2 more | Forest City 2 Nne | Apr 30 | Oct 7 | 159 |
| Fort Dodge | Humboldt, Lehigh, Moorland, Goldfield, Badger, Thor, +8 more | Ft Dodge 5nnw | Apr 28 | Oct 8 | 162 |
| Goose Lake | — | Clinton #1 | Apr 22 | Oct 16 | 175 |
| Grand Mound | — | Davenport | Apr 23 | Oct 15 | 174 |
| Grundy Center | Reinbeck, Dike, Wellsburg, Gladbrook, Lincoln, Stout, +2 more | Grundy Ctr | Apr 29 | Oct 9 | 160 |
| Guthrie Center | Panora, Redfield, Linden, Bayard, Yale | Guthrie Ctr | May 2 | Oct 3 | 153 |
| Hawarden | Akron, Ireton, Alcester, Chatsworth, Hudson | Hawarden | May 1 | Oct 4 | 155 |
| Holstein | Cushing | Holstein | Apr 30 | Oct 9 | 162 |
| Ida Grove | — | Ida Grove 5nw | Apr 27 | Oct 12 | 167 |
| Independence | Jesup, Quasqueton, Hazleton, Aurora, Stanley | Independence #1 | Apr 30 | Oct 7 | 159 |
| Iowa Falls | Ackley, Alden, Radcliffe, Bradford, Dows, Popejoy | Iowa Falls | Apr 28 | Oct 10 | 164 |
| Lake | Rockwell, Manson, Lohrville, Pomeroy, Gowrie, Knierim, +3 more | Rockwell City | Apr 26 | Oct 10 | 167 |
| Lake Park | Harris, Round Lake | Lake Park | Apr 30 | Oct 10 | 164 |
| Le Mars | Kingsley, Remsen, Hinton, Merrill, Brunsville, Oyens | Le Mars | Apr 30 | Oct 4 | 157 |
| Lowden | Wheatland | Lowden | Apr 27 | Oct 10 | 165 |
| Luther | — | Ames 8 Wsw | Apr 23 | Oct 14 | 173 |
| Malcom | Gilman | Grinnell 3 Sw | May 3 | Oct 6 | 155 |
| Manchester | Delhi, Winthrop, Walker, Lamont, Earlville, Ryan, +2 more | Manchester #2 | May 3 | Oct 4 | 154 |
| Mapleton | Anthon, Correctionville, Battle Creek, Charter Oak, Danbury, Smithland, +4 more | Mapleton No.2 | May 3 | Oct 1 | 151 |
| Maquoketa | Delmar, Lost Nation, Spragueville, Oxford Junction, Charlotte, Monmouth, +2 more | Maquoketa | Apr 25 | Oct 14 | 171 |
| Marengo | Conroy, Ladora | Williamsburg 1e | Apr 28 | Oct 9 | 164 |
| Marion | Robins, Hiawatha, Mount Vernon, Lisbon, Springville, Palo, +3 more | Cedar Rapids #1 | Apr 28 | Oct 12 | 166 |
| Marshalltown | Le Grand, Ferguson, Haverhill | Marshalltown | Apr 28 | Oct 7 | 162 |
| Mason | Rockwell, Nora Springs, Manly, Plymouth, Rock Falls | Mason City | Apr 29 | Oct 7 | 161 |
| Monticello | Anamosa, Olin, Martelle, Morley | Anamosa 1 Wnw | May 1 | Oct 4 | 154 |
| New Hampton | Lawler, Fredericksburg, Alta Vista, Ionia, Waucoma | New Hampton | May 2 | Oct 5 | 155 |
| Northwood | Kensett, Carpenter, Grafton | Northwood | May 4 | Oct 4 | 152 |
| Ocheyedan | Ashton, Little Rock | Sibley | May 5 | Oct 3 | 152 |
| Oelwein | — | Oelwein 2 S | Apr 30 | Oct 9 | 163 |
| Okoboji | Arnolds Park, West Okoboji | Milford 4 Nw | May 1 | Oct 6 | 158 |
| Onawa | Whiting | Onawa 3nw | May 1 | Oct 3 | 154 |
| Orleans | Terril, Superior | Spirit Lake | Apr 28 | Oct 11 | 164 |
| Osage | St. Ansgar, Rudd, Meyer, Little Cedar, Stacyville, Orchard | Osage | Apr 30 | Oct 9 | 163 |
| Perry | Woodward, Rippey, Dawson, Jamaica, Minburn, Bouton | Perry | Apr 25 | Oct 10 | 166 |
| Pocahontas | Gilmore, Rolfe, Fonda, Plover, Havelock, Bradgate, +2 more | Pocahontas | Apr 26 | Oct 7 | 164 |
| Postville | Clermont, Luana, Castalia | Postville | May 1 | Oct 3 | 153 |
| Primghar | Paullina, Sutherland, Granville, Calumet, Archer | Primghar | Apr 29 | Oct 10 | 163 |
| Rock Rapids | Luverne, George, Lester, Adrian, Magnolia, Doon, +5 more | Rock Rapids | May 1 | Oct 4 | 156 |
| Sabula | Goose Lake, Andover | Fulton L&d #13 | Apr 13 | Oct 26 | 195 |
| Sac | Lake View, Wall Lake, Odebolt, Auburn, Early, Lytton, +2 more | Sac City | Apr 30 | Oct 6 | 158 |
| Sanborn | Hartley, Melvin | Sanborn | May 1 | Oct 7 | 160 |
| Sheffield | Hampton, Alexander, Coulter, Latimer, Aredale, Dougherty, +3 more | Hampton | Apr 29 | Oct 9 | 162 |
| Sheldon | Boyden, Hospers, Matlock | Sheldon | May 5 | Sep 28 | 145 |
| Sioux | Sergeant Bluff, North Sioux, Salix, Dakota, Climbing Hill, Moville, +7 more | Sioux City Gateway Ap | Apr 29 | Oct 5 | 159 |
| Sioux Center | Orange, Rock Valley, Alton, Hull, Maurice | Sioux Ctr 2 Se | Apr 30 | Oct 3 | 154 |
| Sioux Rapids | Laurens, Marathon, Linn Grove, Albert, Webb, Rembrandt, +2 more | Sioux Rapids 4 E | Apr 30 | Oct 5 | 159 |
| Spencer | Everly, Dickens, Fostoria, Royal | Spencer 1 N | May 1 | Oct 3 | 154 |
| St. Olaf | — | Elkader 6 Ssw | May 8 | Oct 1 | 146 |
| Storm Lake | Newell, Schaller, Alta, Galva, Truesdale | Storm Lake | Apr 25 | Oct 13 | 170 |
| Story | Roland, Randall | Ames Muni Ap | Apr 26 | Oct 8 | 164 |
| Tama | Toledo, Traer, Garwin, Clutier, Montour | Toledo 3n | Apr 30 | Oct 9 | 162 |
| Tipton | Mechanicsville, Stanwood, Clarence, Bennett | Tipton | Apr 21 | Oct 15 | 175 |
| Ute | — | Castana Exp Farm | Apr 25 | Oct 12 | 170 |
| Vinton | Center Point, La Porte, Urbana, Dysart, Van Horne, Shellsburg, +6 more | Vinton | May 3 | Oct 3 | 151 |
| Waterloo | Cedar Falls, Hudson, Denver, Raymond, Janesville, Traer, +4 more | Waterloo Muni Ap | Apr 27 | Oct 10 | 165 |
| Waukon | — | Waukon | May 2 | Oct 11 | 161 |
| Waverly | Sumner, Tripoli, Fairbank, Frederika, Plainfield, Readlyn | Tripoli | Apr 29 | Oct 9 | 162 |
| Webster | Eagle Grove, Jewell Junction, Lehigh, Duncombe, Stratford, Woolstock, +6 more | Webster City | May 3 | Oct 2 | 150 |
| West Union | Fayette, Maynard, Wadena, Elgin, Hawkeye, Westgate, +2 more | Fayette | May 4 | Oct 4 | 151 |
| Westphalia | — | Harlan | Apr 27 | Oct 9 | 165 |
* Clarion is this group's median-season location — the calendar below is computed from its data.
Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.
Planting calendar (Clarion, representative)
Computed from Clarion's average frost dates — the median-season location in this Iowazone 5a group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting | Season fit |
|---|---|---|---|---|---|---|
| Tomato | Tender | Mar 5 – Mar 19 | May 7 – May 14 | Jul 6 – Jul 26 | — | matures comfortably |
| Pepper | Very tender | Feb 19 – Mar 5 | May 14 – May 21 | Jul 13 – Aug 12 | — | matures comfortably |
| Cucumber | Tender | Apr 2 – Apr 9 | May 7 – May 14 | Jun 26 – Jul 16 | — | matures comfortably |
| Summer squash / zucchini | Tender | — | May 7 – May 14 | Jun 21 – Jul 6 | — | matures comfortably |
| Bush bean | Tender | — | May 7 – May 14 | Jun 26 – Jul 6 | Aug 11 – Aug 21 | matures comfortably |
| Sweet corn | Tender | — | Apr 30 – May 14 | Jun 29 – Jul 29 | — | matures comfortably |
| Basil | Very tender | Mar 19 – Apr 2 | May 7 – May 14 | Jun 6 – Jun 21 | — | matures comfortably |
| Lettuce | Half-hardy | Mar 19 – Apr 2 | Apr 2 – Apr 16 | May 17 – Jun 1 | Jul 28 – Aug 12 | matures comfortably |
| Pea | Hardy | — | Mar 19 – Apr 2 | May 13 – May 28 | Jul 18 – Aug 2 | matures comfortably |
| Spinach | Hardy | — | Mar 19 – Apr 2 | Apr 28 – May 8 | Aug 7 – Aug 17 | matures comfortably |
| Carrot | Half-hardy | — | Apr 9 – Apr 16 | Jun 8 – Jun 28 | Jul 8 – Jul 28 | matures comfortably |
| Broccoli | Half-hardy | Mar 5 – Mar 19 | Apr 2 – Apr 16 | May 27 – Jun 16 | Jul 13 – Aug 2 | matures comfortably |
Which crops fit this growing season
Using Clarion's own 162-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.
Frost & freeze dates (Clarion)
From NOAA's 1991–2020 Climate Normals at station USC00131541. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.
| Threshold | Last spring — avg | Last spring — 90%-safe | First fall — avg | First fall — 90%-safe | Season (days) |
|---|---|---|---|---|---|
| 36°F | May 8 | May 21 | Oct 1 | Oct 12 | 143 |
| 32°F (freeze) | Apr 30 | May 12 | Oct 10 | Oct 21 | 162 |
| 28°F | Apr 19 | May 3 | Oct 19 | Oct 31 | 181 |
| 24°F | Apr 10 | Apr 26 | Oct 29 | Nov 10 | 201 |
Growing degree days
Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 89 locations is 2,862; Clarion's own reading is shown below.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 2,971 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 4,989 | cool-season crops (brassicas, greens) |
Hardiness zone 5a in Iowa
Zone 5a means an average annual extreme minimum winter temperature of about −20 to −15 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Iowa spans 4 hardiness zones in this dataset — see all Iowa locations for the full range, including zones4b, 5b, 6a.
Explore zone 5a in other states at zone 5a, or see all USDA hardiness zones.
Frequently asked questions
- What does USDA hardiness zone 5a mean in Iowa?
- Zone 5a means an average annual extreme minimum winter temperature of −20 to −15 °F — the standard USDA measure of which perennials survive winter. 89 locations in Iowa fall in this zone. It does not set planting dates; see the frost calendar below for that.
- Where in Iowa's zone 5a is the growing season longest?
- Sabula runs the longest season on this page at about 195 days; Sheldon is shortest at about 145 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
- When should I plant tomatoes in Iowa's zone 5a?
- Using Clarion's frost dates (this page's median-season location): start seeds indoors about Mar 5 – Mar 19, then transplant outside about May 7 – May 14. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
- Does every location in Iowa's zone 5a have the same frost dates?
- No — they do not all share a weather station, so frost dates vary by a week or more across the 89 locations listed (see the table above for each location's own dates).
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.