Jefferson, IA frost dates
Last spring frostApr 26median date
First fall frostOct 9median date
Growing season166 daysfrost-free
Hardiness zone5bZone 5b
How Jefferson compares
- In 8 years out of 10, the last spring frost in Jefferson falls between April 12 and May 8, a 26-day window. The first fall frost falls between September 23 and October 24.
- The median last frost is 2 days earlier than the Iowa median of Apr 28.
- Its 166-day growing season is longer than 52% of the 934 Iowa places with a regular frost season (state median 165 days).
- The last frost is 5 days earlier than the zone 5b median of May 1. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 5b chart.
- The weather station records an average of 149 nights a year at or below 32°F.
- Compared with Ames, IA, 64 km away, the last frost here is the same as there and the growing season is 1 day longer.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 12 |
| 50% (median) | April 26 |
| 10% (safe for tender plants) | May 8 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 23 |
| 50% (median) | October 9 |
| 90% (late) | October 24 |
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 Jefferson, IA
Jefferson, IA frost dates — last frost Apr 26, first frost Oct 9, zone 5b. whenisthelastfrost.com
Crop
JFMAMJJASOND
Start indoors: Feb 1 to Feb 15Transplant outside: Mar 29 to Apr 12
Start indoors: Feb 15 to Mar 1Transplant outside: May 10 to May 24
Start indoors: Feb 15 to Mar 1Transplant outside: May 10 to May 24
Start indoors: Mar 1 to Mar 15Transplant outside: May 3 to May 17
Start indoors: Mar 1 to Mar 15Transplant outside: Apr 5 to Apr 19Sow outdoors: Mar 29 to May 3Plant for fall: Aug 14 to Sep 11
Start indoors: Mar 1 to Mar 15Transplant outside: Mar 29 to Apr 12Sow outdoors: Mar 29 to Apr 12Plant for fall: Jul 31 to Aug 21
Start indoors: Mar 1 to Mar 15Transplant outside: Apr 12 to Apr 26Plant for fall: Jul 3 to Jul 24
Start indoors: Mar 1 to Mar 15Transplant outside: Apr 5 to Apr 19Plant for fall: Jul 3 to Jul 24
Start indoors: Mar 1 to Mar 15Transplant outside: Apr 12 to Apr 26Plant for fall: Jul 3 to Jul 24
Start indoors: Mar 15 to Mar 29Transplant outside: May 17 to May 31Sow outdoors: May 17 to May 31
Start indoors: Mar 15 to Mar 29Transplant outside: May 3 to May 17
Sow outdoors: Mar 15 to Apr 5Plant for fall: Jul 17 to Aug 7
Sow outdoors: Mar 15 to Apr 5Plant for fall: Aug 14 to Sep 4
Sow outdoors: Mar 22 to May 3Plant for fall: Aug 28 to Sep 18
Start indoors: Mar 29 to Apr 5Transplant outside: May 10 to May 17Sow outdoors: May 3 to May 17Plant for fall: Jul 24 to Aug 7
Start indoors: Mar 29 to Apr 5Sow outdoors: May 3 to May 17Plant for fall: Jul 31 to Aug 14
Start indoors: Mar 29 to Apr 5Sow outdoors: May 3 to May 17
Start indoors: Mar 29 to Apr 5Transplant outside: May 10 to May 24
Sow outdoors: Apr 5 to May 3Plant for fall: Jul 17 to Jul 31
Sow outdoors: Apr 5 to May 3Plant for fall: Jul 31 to Aug 14
Sow outdoors: Apr 5 to Apr 26
Sow outdoors: Apr 12 to May 10Plant for fall: Jul 31 to Aug 14
Sow outdoors: Apr 12 to May 3Plant for fall: Aug 14 to Sep 4
Sow outdoors: May 3 to May 24Plant for fall: Jul 24 to Aug 7
Sow outdoors: May 3 to May 17
Transplant outside: May 10 to May 31
Plant for fall: Sep 25 to Oct 30
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Jefferson, IA
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 1 – Feb 15 | Mar 29 – Apr 12 | — | — |
| Peppers | Feb 15 – Mar 1 | May 10 – May 24 | — | — |
| Eggplant | Feb 15 – Mar 1 | May 10 – May 24 | — | — |
| Tomatoes | Mar 1 – Mar 15 | May 3 – May 17 | — | — |
| Lettuce | Mar 1 – Mar 15 | Apr 5 – Apr 19 | Mar 29 – May 3 | Aug 14 – Sep 11 |
| Kale | Mar 1 – Mar 15 | Mar 29 – Apr 12 | Mar 29 – Apr 12 | Jul 31 – Aug 21 |
| Broccoli | Mar 1 – Mar 15 | Apr 12 – Apr 26 | — | Jul 3 – Jul 24 |
| Cabbage | Mar 1 – Mar 15 | Apr 5 – Apr 19 | — | Jul 3 – Jul 24 |
| Cauliflower | Mar 1 – Mar 15 | Apr 12 – Apr 26 | — | Jul 3 – Jul 24 |
| Okra | Mar 15 – Mar 29 | May 17 – May 31 | May 17 – May 31 | — |
| Basil | Mar 15 – Mar 29 | May 3 – May 17 | — | — |
| Peas | — | — | Mar 15 – Apr 5 | Jul 17 – Aug 7 |
| Spinach | — | — | Mar 15 – Apr 5 | Aug 14 – Sep 4 |
| Radishes | — | — | Mar 22 – May 3 | Aug 28 – Sep 18 |
| Cucumbers | Mar 29 – Apr 5 | May 10 – May 17 | May 3 – May 17 | Jul 24 – Aug 7 |
| Zucchini & Summer Squash | Mar 29 – Apr 5 | — | May 3 – May 17 | Jul 31 – Aug 14 |
| Winter Squash & Pumpkins | Mar 29 – Apr 5 | — | May 3 – May 17 | — |
| Melons & Watermelon | Mar 29 – Apr 5 | May 10 – May 24 | — | — |
| Carrots | — | — | Apr 5 – May 3 | Jul 17 – Jul 31 |
| Beets | — | — | Apr 5 – May 3 | Jul 31 – Aug 14 |
| Potatoes | — | — | Apr 5 – Apr 26 | — |
| Swiss Chard | — | — | Apr 12 – May 10 | Jul 31 – Aug 14 |
| Cilantro | — | — | Apr 12 – May 3 | Aug 14 – Sep 4 |
| Green Beans | — | — | May 3 – May 24 | Jul 24 – Aug 7 |
| Sweet Corn | — | — | May 3 – May 17 | — |
| Sweet Potatoes | — | May 10 – May 31 | — | — |
| Garlic | — | — | — | Sep 25 – Oct 30 |
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 Jefferson, IA weather station, about 1 km away (elevation 1,056 ft (322 m)).
Frost dates near Jefferson
- Cooper Apr 26 · Oct 9
- Grand Junction Apr 26 · Oct 9
- Scranton Apr 26 · Oct 9
- Dana Apr 26 · Oct 9
- Rippey Apr 25 · Oct 10
- Churdan Apr 26 · Oct 9
- Jamaica Apr 25 · Oct 10
- Paton Apr 26 · Oct 9
- Bagley May 2 · Oct 3
- Ralston Apr 27 · Oct 10
Frequently asked questions
When is the last frost in Jefferson, IA?
The median last spring frost in Jefferson, IA is April 26. There is still about a 10% chance of frost after May 8, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Jefferson, IA?
The median first fall frost is October 9, with about a 10% chance of frost before September 23.
How long is the growing season in Jefferson, IA?
About 166 days between the median last spring frost and first fall frost.
What planting zone is Jefferson, IA?
Jefferson, IA is in USDA hardiness zone 5b.