Grinnell, IA frost dates
Last spring frostMay 3median date
First fall frostOct 6median date
Growing season156 daysfrost-free
Hardiness zone5bZone 5b
How Grinnell compares
- In 8 years out of 10, the last spring frost in Grinnell falls between April 19 and May 17, a 28-day window. The first fall frost falls between September 22 and October 20.
- The median last frost is 5 days later than the Iowa median of Apr 28.
- Its 156-day growing season is longer than 15% of the 934 Iowa places with a regular frost season (state median 165 days).
- The last frost is typical for zone 5b, where the median is May 1.
- The weather station records an average of 157 nights a year at or below 32°F.
- Compared with Des Moines, IA, 71 km away, the last frost here is 10 days later than there and the growing season is 19 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 19 |
| 50% (median) | May 3 |
| 10% (safe for tender plants) | May 17 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 22 |
| 50% (median) | October 6 |
| 90% (late) | October 20 |
Frost here means 32°F (0°C). A median date means half of years have their last frost earlier and half later.
Planting calendar for Grinnell, IA
Grinnell, IA frost dates — last frost May 3, first frost Oct 6, zone 5b. whenisthelastfrost.com
Crop
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Start indoors: Feb 8 to Feb 22Transplant outside: Apr 5 to Apr 19
Start indoors: Feb 22 to Mar 8Transplant outside: May 17 to May 31
Start indoors: Feb 22 to Mar 8Transplant outside: May 17 to May 31
Start indoors: Mar 8 to Mar 22Transplant outside: May 10 to May 24
Start indoors: Mar 8 to Mar 22Transplant outside: Apr 12 to Apr 26Sow outdoors: Apr 5 to May 10Plant for fall: Aug 11 to Sep 8
Start indoors: Mar 8 to Mar 22Transplant outside: Apr 5 to Apr 19Sow outdoors: Apr 5 to Apr 19Plant for fall: Jul 28 to Aug 18
Start indoors: Mar 8 to Mar 22Transplant outside: Apr 19 to May 3Plant for fall: Jun 30 to Jul 21
Start indoors: Mar 8 to Mar 22Transplant outside: Apr 12 to Apr 26Plant for fall: Jun 30 to Jul 21
Start indoors: Mar 8 to Mar 22Transplant outside: Apr 19 to May 3Plant for fall: Jun 30 to Jul 21
Start indoors: Mar 22 to Apr 5Transplant outside: May 24 to Jun 7Sow outdoors: May 24 to Jun 7
Start indoors: Mar 22 to Apr 5Transplant outside: May 10 to May 24
Sow outdoors: Mar 22 to Apr 12Plant for fall: Jul 14 to Aug 4
Sow outdoors: Mar 22 to Apr 12Plant for fall: Aug 11 to Sep 1
Sow outdoors: Mar 29 to May 10Plant for fall: Aug 25 to Sep 15
Start indoors: Apr 5 to Apr 12Transplant outside: May 17 to May 24Sow outdoors: May 10 to May 24Plant for fall: Jul 21 to Aug 4
Start indoors: Apr 5 to Apr 12Sow outdoors: May 10 to May 24Plant for fall: Jul 28 to Aug 11
Start indoors: Apr 5 to Apr 12Sow outdoors: May 10 to May 24
Start indoors: Apr 5 to Apr 12Transplant outside: May 17 to May 31
Sow outdoors: Apr 12 to May 10Plant for fall: Jul 14 to Jul 28
Sow outdoors: Apr 12 to May 10Plant for fall: Jul 28 to Aug 11
Sow outdoors: Apr 12 to May 3
Sow outdoors: Apr 19 to May 17Plant for fall: Jul 28 to Aug 11
Sow outdoors: Apr 19 to May 10Plant for fall: Aug 11 to Sep 1
Sow outdoors: May 10 to May 31Plant for fall: Jul 21 to Aug 4
Sow outdoors: May 10 to May 24
Transplant outside: May 17 to Jun 7
Plant for fall: Sep 22 to Oct 27
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Grinnell, IA
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 8 – Feb 22 | Apr 5 – Apr 19 | — | — |
| Peppers | Feb 22 – Mar 8 | May 17 – May 31 | — | — |
| Eggplant | Feb 22 – Mar 8 | May 17 – May 31 | — | — |
| Tomatoes | Mar 8 – Mar 22 | May 10 – May 24 | — | — |
| Lettuce | Mar 8 – Mar 22 | Apr 12 – Apr 26 | Apr 5 – May 10 | Aug 11 – Sep 8 |
| Kale | Mar 8 – Mar 22 | Apr 5 – Apr 19 | Apr 5 – Apr 19 | Jul 28 – Aug 18 |
| Broccoli | Mar 8 – Mar 22 | Apr 19 – May 3 | — | Jun 30 – Jul 21 |
| Cabbage | Mar 8 – Mar 22 | Apr 12 – Apr 26 | — | Jun 30 – Jul 21 |
| Cauliflower | Mar 8 – Mar 22 | Apr 19 – May 3 | — | Jun 30 – Jul 21 |
| Okra | Mar 22 – Apr 5 | May 24 – Jun 7 | May 24 – Jun 7 | — |
| Basil | Mar 22 – Apr 5 | May 10 – May 24 | — | — |
| Peas | — | — | Mar 22 – Apr 12 | Jul 14 – Aug 4 |
| Spinach | — | — | Mar 22 – Apr 12 | Aug 11 – Sep 1 |
| Radishes | — | — | Mar 29 – May 10 | Aug 25 – Sep 15 |
| Cucumbers | Apr 5 – Apr 12 | May 17 – May 24 | May 10 – May 24 | Jul 21 – Aug 4 |
| Zucchini & Summer Squash | Apr 5 – Apr 12 | — | May 10 – May 24 | Jul 28 – Aug 11 |
| Winter Squash & Pumpkins | Apr 5 – Apr 12 | — | May 10 – May 24 | — |
| Melons & Watermelon | Apr 5 – Apr 12 | May 17 – May 31 | — | — |
| Carrots | — | — | Apr 12 – May 10 | Jul 14 – Jul 28 |
| Beets | — | — | Apr 12 – May 10 | Jul 28 – Aug 11 |
| Potatoes | — | — | Apr 12 – May 3 | — |
| Swiss Chard | — | — | Apr 19 – May 17 | Jul 28 – Aug 11 |
| Cilantro | — | — | Apr 19 – May 10 | Aug 11 – Sep 1 |
| Green Beans | — | — | May 10 – May 31 | Jul 21 – Aug 4 |
| Sweet Corn | — | — | May 10 – May 24 | — |
| Sweet Potatoes | — | May 17 – Jun 7 | — | — |
| Garlic | — | — | — | Sep 22 – Oct 27 |
Dates come from the median frost dates and common extension-service timing. Adjust for your soil temperature, microclimate and the varieties you grow.
About these dates
Based on 1991–2020 NOAA climate normals for the Grinnell 3 Sw, IA weather station, 3 km away (elevation 906 ft (276 m)).
Frost dates near Grinnell
- Kellogg Apr 22 · Oct 17
- Malcom May 3 · Oct 6
- Gilman Apr 28 · Oct 7
- Lynnville May 3 · Oct 6
- Searsboro May 3 · Oct 6
- Killduff Apr 22 · Oct 17
- Sully May 3 · Oct 6
- Laurel Apr 28 · Oct 7
- Montezuma May 3 · Oct 6
- Ferguson Apr 28 · Oct 7
Frequently asked questions
When is the last frost in Grinnell, IA?
The median last spring frost in Grinnell, IA is May 3. There is still about a 10% chance of frost after May 17, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Grinnell, IA?
The median first fall frost is October 6, with about a 10% chance of frost before September 22.
How long is the growing season in Grinnell, IA?
About 156 days between the median last spring frost and first fall frost.
What planting zone is Grinnell, IA?
Grinnell, IA is in USDA hardiness zone 5b.