USDA zone 5b in Iowa
USDA plant hardiness zone 5b covers 70 locations across Iowa (average annual extreme minimum −15 to −10 °F): Adair, IA, Adel, IA, Albia, IA, Ames, IA, Ames, IA, Anita, IA, and 64 more. Average last spring frost across this group ranges April 13 (Clinton) to May 5 (Chariton), and growing seasons run 151–195 days (Chariton to Clinton) — 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 Castana, this group's median-season location.
- USDA zone
- 5b−15 to −10 °F
- Last frost range
- Apr 13–May 5avg, 32°F
- First frost range
- Oct 2–Oct 26avg, 32°F
- Growing season range
- 151–195days
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) |
|---|---|---|---|---|---|
| Adair | Casey, Menlo | Guthrie Ctr | May 2 | Oct 3 | 153 |
| Adel | — | Perry | Apr 25 | Oct 10 | 166 |
| Albia | Moravia, Eddyville, Lovilia, Bussey, Blakesburg | Albia 3 Nne | Apr 24 | Oct 16 | 173 |
| Ames | Gilbert, Kelley | Ames Muni Ap | Apr 26 | Oct 8 | 164 |
| Ames | Madrid | Ames 8 Wsw | Apr 23 | Oct 14 | 173 |
| Anita | Cumberland, Marne, Lewis, Wiota | Atlantic 1 Ne | Apr 30 | Oct 2 | 153 |
| Ankeny | Altoona, Bondurant, Saylorville, Alleman, Elkhart, Sheldahl | Ankeny | Apr 23 | Oct 15 | 173 |
| Arion | — | Denison | Apr 27 | Oct 11 | 166 |
| Avoca | Oakland, Hancock, Carson, Treynor, Griswold, Minden, +3 more | Oakland | Apr 23 | Oct 14 | 174 |
| Bedford | Blockton, Sharpsburg, Gravity, Sheridan | Bedford | Apr 24 | Oct 15 | 173 |
| Bettendorf | East Moline, Le Claire, Princeton, Port Byron, Rapids, Hampton, +2 more | Le Claire L&d 14 | Apr 16 | Oct 25 | 190 |
| Bloomfield | Lancaster, Eldon, Moulton, Unionville, Glenwood, Floris, +4 more | Bloomfield | Apr 16 | Oct 22 | 188 |
| Castana * | Soldier, Moorhead | Castana Exp Farm | Apr 25 | Oct 12 | 170 |
| Cedar Rapids | Bertram | Cedar Rapids #1 | Apr 28 | Oct 12 | 166 |
| Centerville | Exline | Centerville | Apr 28 | Oct 14 | 168 |
| Chariton | Russell, Melrose, Lucas, Plano, Williamson, Lacona, +3 more | Chariton 1 E | May 5 | Oct 5 | 151 |
| Clarinda | College Springs, Braddyville, Blanchard, New Market, Shambaugh, Yorktown, +2 more | Clarinda | Apr 25 | Oct 11 | 168 |
| Clinton | Fulton, Thomson | Fulton L&d #13 | Apr 13 | Oct 26 | 195 |
| Collins | — | Colo | Apr 24 | Oct 12 | 170 |
| Columbus Junction | Conesville, Columbus | Columbus Junction | Apr 26 | Oct 10 | 167 |
| Council Bluffs | Underwood, Crescent, Bennington, Fort Calhoun, Loveland | Omaha Eppley Airfield | Apr 18 | Oct 21 | 185 |
| Creston | Lenox, Afton, Arispe, Shannon, Cromwell | Creston 2 Sw | Apr 28 | Oct 11 | 164 |
| Davenport | Bettendorf, Park View, Calamus, Donahue, Maysville, Dixon, +2 more | Davenport | Apr 23 | Oct 15 | 174 |
| Davenport | Rock Island, Blue Grass, Andalusia, Montpelier | Rock Island L&d 15 | Apr 19 | Oct 22 | 184 |
| Decatur | Pleasanton | Lamoni Muni Ap | Apr 16 | Oct 21 | 186 |
| Des Moines | West Des Moines, Urbandale, Norwalk, Pleasant Hill, Carlisle, Van Meter, +2 more | Des Moines Intl Ap | Apr 18 | Oct 20 | 184 |
| DeWitt | Albany, Cordova, McCausland, Low Moor | Clinton #1 | Apr 22 | Oct 16 | 175 |
| Fairfield | Richland, Packwood, Lockridge, Batavia, Libertyville | Fairfield | Apr 27 | Oct 12 | 168 |
| Grinnell | Montezuma, Lynnville, Sully, Searsboro | Grinnell 3 Sw | May 3 | Oct 6 | 155 |
| Guernsey | — | Belle Plaine | Apr 28 | Oct 10 | 165 |
| Hamburg | Riverton, Thurman, Anderson, Randolph | Sidney 1sse | Apr 19 | Oct 19 | 182 |
| Harlan | Shelby, Earling, Panama | Harlan | Apr 27 | Oct 9 | 165 |
| Indianola | St. Charles, Milo, Ackworth, Bevington, New Virginia, Martensdale, +2 more | Indianola 2w | Apr 24 | Oct 12 | 168 |
| Iowa | West Branch, Riverside, West Liberty, Lone Tree, Hills | Iowa City | Apr 29 | Oct 9 | 162 |
| Iowa | Coralville, Tiffin, Kalona, Solon, Oxford, University Heights | Iowa City Muni Ap | Apr 21 | Oct 18 | 180 |
| Jefferson | — | Jefferson | Apr 26 | Oct 9 | 164 |
| Kimballton | — | Audubon | May 2 | Oct 3 | 154 |
| Lamoni | Eagleville, Allendale, Blythedale | Lamoni | Apr 17 | Oct 21 | 184 |
| Leon | Lineville, Garden Grove, Humeston | Leon 6 Ese | Apr 30 | Oct 8 | 161 |
| Malvern | Pacific Junction, Mineola | Glenwood 3sw | Apr 23 | Oct 11 | 170 |
| Melbourne | — | Marshalltown | Apr 28 | Oct 7 | 162 |
| Milton | Douds, Leando, Keosauqua, Birmingham | Keosauqua | Apr 26 | Oct 13 | 169 |
| Missouri Valley | Woodbine, Dunlap, Logan, Neola, Magnolia, Persia, +1 more | Logan | Apr 29 | Oct 8 | 162 |
| Mitchellville | Prairie, Hartford, Swan, Runnells | Des Moines 17 E | Apr 21 | Oct 15 | 174 |
| Modale | Mondamin | Tekamah Muni Ap | Apr 23 | Oct 8 | 166 |
| Mount Ayr | Clearfield, Redding, Diagonal, Benton, Allendale | Mt Ayr | Apr 25 | Oct 12 | 169 |
| Muscatine | Wilton, Fruitland, Durant, Moscow, Letts, Illinois, +2 more | Muscatine | Apr 24 | Oct 14 | 172 |
| Mystic | — | Rathbun Dam | Apr 18 | Oct 23 | 187 |
| Nevada | Huxley, Cambridge, Maxwell | Ames 5 Se | Apr 26 | Oct 12 | 168 |
| Newton | Colfax, Monroe, Rhodes, Baxter, Mingo, Sully, +3 more | Newton | Apr 22 | Oct 17 | 174 |
| North Liberty | Amana | Cedar Rapids Muni Ap | Apr 27 | Oct 11 | 165 |
| Osceola | Murray, Woodburn, Van Wert, Weldon | Osceola | Apr 29 | Oct 9 | 162 |
| Oskaloosa | New Sharon, Beacon, Barnes, Rose Hill, Leighton | Oskaloosa | Apr 21 | Oct 16 | 176 |
| Ottumwa | Hedrick, Fremont, Agency, Kirkville, Chillicothe | Ottumwa Industrial Ap | Apr 23 | Oct 14 | 172 |
| Pella | Knoxville, Pleasantville, Monroe, Melcher-Dallas, Harvey, Marysville, +1 more | Knoxville | Apr 20 | Oct 19 | 180 |
| Percival | Union, Julian | Nebraska City 2nw | Apr 18 | Oct 19 | 182 |
| Pisgah | — | Little Sioux 2 Nw | May 1 | Oct 3 | 155 |
| Red Oak | Stanton, Elliott, Hastings, Emerson | Red Oak | Apr 24 | Oct 13 | 169 |
| Seymour | Corydon, Allerton, Clio, Powersville | Allerton | Apr 21 | Oct 19 | 178 |
| Shenandoah | Essex, Coin, Imogene, Farragut, Northboro, Westboro | Shenandoah | Apr 20 | Oct 17 | 179 |
| Sigourney | What Cheer, Ollie, Delta, Deep River, Martinsburg, South English, +5 more | Sigourney | Apr 24 | Oct 15 | 172 |
| Stuart | Greenfield, Fontanelle, Orient, Bridgewater | Greenfield | Apr 25 | Oct 12 | 170 |
| Sun Valley Lake | Tingley, Kellerton, Grand River, Thayer | Beaconsfield | Apr 23 | Oct 17 | 176 |
| Swedesburg | Yarmouth, New London, Winfield, Olds, Mount Union, Westwood | Mt Pleasant 1 Ssw | Apr 30 | Oct 10 | 163 |
| Urbandale | Waukee, Johnston, Grimes, Polk, Dallas Center, Granger, +1 more | Des Moines Wsfo-johnston | Apr 19 | Oct 18 | 179 |
| Villisca | Corning, Carbon, Grant, Massena, Nodaway, Prescott | Corning | Apr 27 | Oct 12 | 168 |
| Washington | Wellman, Wayland, Brighton, Keota, Ainsworth, Crawfordsville, +1 more | Washington | Apr 28 | Oct 11 | 165 |
| Welton | — | Maquoketa | Apr 25 | Oct 14 | 171 |
| Williamsburg | Homestead, Middle Amana, North English, Parnell, Millersburg | Williamsburg 1e | Apr 28 | Oct 9 | 164 |
| Winterset | Van Meter, Macksburg, De Soto, Dexter, Truro, Earlham, +3 more | Winterset 1s | Apr 30 | Oct 3 | 157 |
* Castana 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 (Castana, representative)
Computed from Castana's average frost dates — the median-season location in this Iowazone 5b 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 | Feb 28 – Mar 14 | May 2 – May 9 | Jul 1 – Jul 21 | — | matures comfortably |
| Pepper | Very tender | Feb 14 – Feb 28 | May 9 – May 16 | Jul 8 – Aug 7 | — | matures comfortably |
| Cucumber | Tender | Mar 28 – Apr 4 | May 2 – May 9 | Jun 21 – Jul 11 | — | matures comfortably |
| Summer squash / zucchini | Tender | — | May 2 – May 9 | Jun 16 – Jul 1 | — | matures comfortably |
| Bush bean | Tender | — | May 2 – May 9 | Jun 21 – Jul 1 | Aug 13 – Aug 23 | matures comfortably |
| Sweet corn | Tender | — | Apr 25 – May 9 | Jun 24 – Jul 24 | — | matures comfortably |
| Basil | Very tender | Mar 14 – Mar 28 | May 2 – May 9 | Jun 1 – Jun 16 | — | matures comfortably |
| Lettuce | Half-hardy | Mar 14 – Mar 28 | Mar 28 – Apr 11 | May 12 – May 27 | Jul 30 – Aug 14 | matures comfortably |
| Pea | Hardy | — | Mar 14 – Mar 28 | May 8 – May 23 | Jul 20 – Aug 4 | matures comfortably |
| Spinach | Hardy | — | Mar 14 – Mar 28 | Apr 23 – May 3 | Aug 9 – Aug 19 | matures comfortably |
| Carrot | Half-hardy | — | Apr 4 – Apr 11 | Jun 3 – Jun 23 | Jul 10 – Jul 30 | matures comfortably |
| Broccoli | Half-hardy | Feb 28 – Mar 14 | Mar 28 – Apr 11 | May 22 – Jun 11 | Jul 15 – Aug 4 | matures comfortably |
Which crops fit this growing season
Using Castana's own 170-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 (Castana)
From NOAA's 1991–2020 Climate Normals at station USC00131277. 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 4 | May 15 | Oct 3 | Oct 17 | 151 |
| 32°F (freeze) | Apr 25 | May 7 | Oct 12 | Oct 27 | 170 |
| 28°F | Apr 15 | Apr 28 | Oct 23 | Nov 4 | 189 |
| 24°F | Apr 6 | Apr 20 | Nov 1 | Nov 14 | 208 |
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 70 locations is 3,206; Castana's own reading is shown below.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 3,036 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 5,123 | cool-season crops (brassicas, greens) |
Hardiness zone 5b in Iowa
Zone 5b means an average annual extreme minimum winter temperature of about −15 to −10 °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, 5a, 6a.
Explore zone 5b in other states at zone 5b, or see all USDA hardiness zones.
Frequently asked questions
- What does USDA hardiness zone 5b mean in Iowa?
- Zone 5b means an average annual extreme minimum winter temperature of −15 to −10 °F — the standard USDA measure of which perennials survive winter. 70 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 5b is the growing season longest?
- Clinton runs the longest season on this page at about 195 days; Chariton is shortest at about 151 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 5b?
- Using Castana's frost dates (this page's median-season location): start seeds indoors about Feb 28 – Mar 14, then transplant outside about May 2 – May 9. 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 5b 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 70 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.