Williamson, IA frost dates
Last spring frostMay 5median date
First fall frostOct 5median date
Growing season153 daysfrost-free
Hardiness zone5bZone 5b
How Williamson compares
- In 8 years out of 10, the last spring frost in Williamson falls between April 21 and May 19, a 28-day window. The first fall frost falls between September 20 and October 18.
- The median last frost is 7 days later than the Iowa median of Apr 28.
- Its 153-day growing season is longer than 6% of the 934 Iowa places with a regular frost season (state median 165 days).
- The last frost is 4 days later 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 154 nights a year at or below 32°F.
- Compared with Des Moines, IA, 68 km away, the last frost here is 12 days later than there and the growing season is 22 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 21 |
| 50% (median) | May 5 |
| 10% (safe for tender plants) | May 19 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 20 |
| 50% (median) | October 5 |
| 90% (late) | October 18 |
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 Williamson, IA
Williamson, IA frost dates — last frost May 5, first frost Oct 5, zone 5b. whenisthelastfrost.com
Crop
JFMAMJJASOND
Start indoors: Feb 10 to Feb 24Transplant outside: Apr 7 to Apr 21
Start indoors: Feb 24 to Mar 10Transplant outside: May 19 to Jun 2
Start indoors: Feb 24 to Mar 10Transplant outside: May 19 to Jun 2
Start indoors: Mar 10 to Mar 24Transplant outside: May 12 to May 26
Start indoors: Mar 10 to Mar 24Transplant outside: Apr 14 to Apr 28Sow outdoors: Apr 7 to May 12Plant for fall: Aug 10 to Sep 7
Start indoors: Mar 10 to Mar 24Transplant outside: Apr 7 to Apr 21Sow outdoors: Apr 7 to Apr 21Plant for fall: Jul 27 to Aug 17
Start indoors: Mar 10 to Mar 24Transplant outside: Apr 21 to May 5Plant for fall: Jun 29 to Jul 20
Start indoors: Mar 10 to Mar 24Transplant outside: Apr 14 to Apr 28Plant for fall: Jun 29 to Jul 20
Start indoors: Mar 10 to Mar 24Transplant outside: Apr 21 to May 5Plant for fall: Jun 29 to Jul 20
Start indoors: Mar 24 to Apr 7Transplant outside: May 26 to Jun 9Sow outdoors: May 26 to Jun 9
Start indoors: Mar 24 to Apr 7Transplant outside: May 12 to May 26
Sow outdoors: Mar 24 to Apr 14Plant for fall: Jul 13 to Aug 3
Sow outdoors: Mar 24 to Apr 14Plant for fall: Aug 10 to Aug 31
Sow outdoors: Mar 31 to May 12Plant for fall: Aug 24 to Sep 14
Start indoors: Apr 7 to Apr 14Transplant outside: May 19 to May 26Sow outdoors: May 12 to May 26Plant for fall: Jul 20 to Aug 3
Start indoors: Apr 7 to Apr 14Sow outdoors: May 12 to May 26Plant for fall: Jul 27 to Aug 10
Start indoors: Apr 7 to Apr 14Sow outdoors: May 12 to May 26
Start indoors: Apr 7 to Apr 14Transplant outside: May 19 to Jun 2
Sow outdoors: Apr 14 to May 12Plant for fall: Jul 13 to Jul 27
Sow outdoors: Apr 14 to May 12Plant for fall: Jul 27 to Aug 10
Sow outdoors: Apr 14 to May 5
Sow outdoors: Apr 21 to May 19Plant for fall: Jul 27 to Aug 10
Sow outdoors: Apr 21 to May 12Plant for fall: Aug 10 to Aug 31
Sow outdoors: May 12 to Jun 2Plant for fall: Jul 20 to Aug 3
Sow outdoors: May 12 to May 26
Transplant outside: May 19 to Jun 9
Plant for fall: Sep 21 to Oct 26
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Williamson, IA
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 10 – Feb 24 | Apr 7 – Apr 21 | — | — |
| Peppers | Feb 24 – Mar 10 | May 19 – Jun 2 | — | — |
| Eggplant | Feb 24 – Mar 10 | May 19 – Jun 2 | — | — |
| Tomatoes | Mar 10 – Mar 24 | May 12 – May 26 | — | — |
| Lettuce | Mar 10 – Mar 24 | Apr 14 – Apr 28 | Apr 7 – May 12 | Aug 10 – Sep 7 |
| Kale | Mar 10 – Mar 24 | Apr 7 – Apr 21 | Apr 7 – Apr 21 | Jul 27 – Aug 17 |
| Broccoli | Mar 10 – Mar 24 | Apr 21 – May 5 | — | Jun 29 – Jul 20 |
| Cabbage | Mar 10 – Mar 24 | Apr 14 – Apr 28 | — | Jun 29 – Jul 20 |
| Cauliflower | Mar 10 – Mar 24 | Apr 21 – May 5 | — | Jun 29 – Jul 20 |
| Okra | Mar 24 – Apr 7 | May 26 – Jun 9 | May 26 – Jun 9 | — |
| Basil | Mar 24 – Apr 7 | May 12 – May 26 | — | — |
| Peas | — | — | Mar 24 – Apr 14 | Jul 13 – Aug 3 |
| Spinach | — | — | Mar 24 – Apr 14 | Aug 10 – Aug 31 |
| Radishes | — | — | Mar 31 – May 12 | Aug 24 – Sep 14 |
| Cucumbers | Apr 7 – Apr 14 | May 19 – May 26 | May 12 – May 26 | Jul 20 – Aug 3 |
| Zucchini & Summer Squash | Apr 7 – Apr 14 | — | May 12 – May 26 | Jul 27 – Aug 10 |
| Winter Squash & Pumpkins | Apr 7 – Apr 14 | — | May 12 – May 26 | — |
| Melons & Watermelon | Apr 7 – Apr 14 | May 19 – Jun 2 | — | — |
| Carrots | — | — | Apr 14 – May 12 | Jul 13 – Jul 27 |
| Beets | — | — | Apr 14 – May 12 | Jul 27 – Aug 10 |
| Potatoes | — | — | Apr 14 – May 5 | — |
| Swiss Chard | — | — | Apr 21 – May 19 | Jul 27 – Aug 10 |
| Cilantro | — | — | Apr 21 – May 12 | Aug 10 – Aug 31 |
| Green Beans | — | — | May 12 – Jun 2 | Jul 20 – Aug 3 |
| Sweet Corn | — | — | May 12 – May 26 | — |
| Sweet Potatoes | — | May 19 – Jun 9 | — | — |
| Garlic | — | — | — | Sep 21 – Oct 26 |
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 Chariton 1 E, IA weather station, 9 km away (elevation 965 ft (294 m)).
Frost dates near Williamson
- Chariton May 5 · Oct 5
- Columbia Apr 20 · Oct 19
- Melcher Dallas Apr 20 · Oct 19
- Lacona May 5 · Oct 5
- Russell May 5 · Oct 5
- Lucas May 5 · Oct 5
- Liberty Center Apr 24 · Oct 12
- Melrose Apr 18 · Oct 23
- Derby May 5 · Oct 5
- Milo Apr 24 · Oct 12
Frequently asked questions
When is the last frost in Williamson, IA?
The median last spring frost in Williamson, IA is May 5. There is still about a 10% chance of frost after May 19, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Williamson, IA?
The median first fall frost is October 5, with about a 10% chance of frost before September 20.
How long is the growing season in Williamson, IA?
About 153 days between the median last spring frost and first fall frost.
What planting zone is Williamson, IA?
Williamson, IA is in USDA hardiness zone 5b.