Winthrop, IA frost dates
Last spring frostApr 30median date
First fall frostOct 7median date
Growing season160 daysfrost-free
Hardiness zone5aZone 5a
How Winthrop compares
- In 8 years out of 10, the last spring frost in Winthrop falls between April 16 and May 12, a 26-day window. The first fall frost falls between September 23 and October 21.
- The median last frost is 2 days later than the Iowa median of Apr 28.
- Its 160-day growing season is longer than 27% of the 934 Iowa places with a regular frost season (state median 165 days).
- The last frost is typical for zone 5a, where the median is May 3.
- The weather station records an average of 151 nights a year at or below 32°F.
- Compared with Waterloo, IA, 50 km away, the last frost here is 3 days later than there and the growing season is 6 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 16 |
| 50% (median) | April 30 |
| 10% (safe for tender plants) | May 12 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 23 |
| 50% (median) | October 7 |
| 90% (late) | October 21 |
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 Winthrop, IA
Winthrop, IA frost dates — last frost Apr 30, first frost Oct 7, zone 5a. whenisthelastfrost.com
Crop
JFMAMJJASOND
Start indoors: Feb 5 to Feb 19Transplant outside: Apr 2 to Apr 16
Start indoors: Feb 19 to Mar 5Transplant outside: May 14 to May 28
Start indoors: Feb 19 to Mar 5Transplant outside: May 14 to May 28
Start indoors: Mar 5 to Mar 19Transplant outside: May 7 to May 21
Start indoors: Mar 5 to Mar 19Transplant outside: Apr 9 to Apr 23Sow outdoors: Apr 2 to May 7Plant for fall: Aug 12 to Sep 9
Start indoors: Mar 5 to Mar 19Transplant outside: Apr 2 to Apr 16Sow outdoors: Apr 2 to Apr 16Plant for fall: Jul 29 to Aug 19
Start indoors: Mar 5 to Mar 19Transplant outside: Apr 16 to Apr 30Plant for fall: Jul 1 to Jul 22
Start indoors: Mar 5 to Mar 19Transplant outside: Apr 9 to Apr 23Plant for fall: Jul 1 to Jul 22
Start indoors: Mar 5 to Mar 19Transplant outside: Apr 16 to Apr 30Plant for fall: Jul 1 to Jul 22
Start indoors: Mar 19 to Apr 2Transplant outside: May 21 to Jun 4Sow outdoors: May 21 to Jun 4
Start indoors: Mar 19 to Apr 2Transplant outside: May 7 to May 21
Sow outdoors: Mar 19 to Apr 9Plant for fall: Jul 15 to Aug 5
Sow outdoors: Mar 19 to Apr 9Plant for fall: Aug 12 to Sep 2
Sow outdoors: Mar 26 to May 7Plant for fall: Aug 26 to Sep 16
Start indoors: Apr 2 to Apr 9Transplant outside: May 14 to May 21Sow outdoors: May 7 to May 21Plant for fall: Jul 22 to Aug 5
Start indoors: Apr 2 to Apr 9Sow outdoors: May 7 to May 21Plant for fall: Jul 29 to Aug 12
Start indoors: Apr 2 to Apr 9Sow outdoors: May 7 to May 21
Start indoors: Apr 2 to Apr 9Transplant outside: May 14 to May 28
Sow outdoors: Apr 9 to May 7Plant for fall: Jul 15 to Jul 29
Sow outdoors: Apr 9 to May 7Plant for fall: Jul 29 to Aug 12
Sow outdoors: Apr 9 to Apr 30
Sow outdoors: Apr 16 to May 14Plant for fall: Jul 29 to Aug 12
Sow outdoors: Apr 16 to May 7Plant for fall: Aug 12 to Sep 2
Sow outdoors: May 7 to May 28Plant for fall: Jul 22 to Aug 5
Sow outdoors: May 7 to May 21
Transplant outside: May 14 to Jun 4
Plant for fall: Sep 23 to Oct 28
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Winthrop, IA
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 5 – Feb 19 | Apr 2 – Apr 16 | — | — |
| Peppers | Feb 19 – Mar 5 | May 14 – May 28 | — | — |
| Eggplant | Feb 19 – Mar 5 | May 14 – May 28 | — | — |
| Tomatoes | Mar 5 – Mar 19 | May 7 – May 21 | — | — |
| Lettuce | Mar 5 – Mar 19 | Apr 9 – Apr 23 | Apr 2 – May 7 | Aug 12 – Sep 9 |
| Kale | Mar 5 – Mar 19 | Apr 2 – Apr 16 | Apr 2 – Apr 16 | Jul 29 – Aug 19 |
| Broccoli | Mar 5 – Mar 19 | Apr 16 – Apr 30 | — | Jul 1 – Jul 22 |
| Cabbage | Mar 5 – Mar 19 | Apr 9 – Apr 23 | — | Jul 1 – Jul 22 |
| Cauliflower | Mar 5 – Mar 19 | Apr 16 – Apr 30 | — | Jul 1 – Jul 22 |
| Okra | Mar 19 – Apr 2 | May 21 – Jun 4 | May 21 – Jun 4 | — |
| Basil | Mar 19 – Apr 2 | May 7 – May 21 | — | — |
| Peas | — | — | Mar 19 – Apr 9 | Jul 15 – Aug 5 |
| Spinach | — | — | Mar 19 – Apr 9 | Aug 12 – Sep 2 |
| Radishes | — | — | Mar 26 – May 7 | Aug 26 – Sep 16 |
| Cucumbers | Apr 2 – Apr 9 | May 14 – May 21 | May 7 – May 21 | Jul 22 – Aug 5 |
| Zucchini & Summer Squash | Apr 2 – Apr 9 | — | May 7 – May 21 | Jul 29 – Aug 12 |
| Winter Squash & Pumpkins | Apr 2 – Apr 9 | — | May 7 – May 21 | — |
| Melons & Watermelon | Apr 2 – Apr 9 | May 14 – May 28 | — | — |
| Carrots | — | — | Apr 9 – May 7 | Jul 15 – Jul 29 |
| Beets | — | — | Apr 9 – May 7 | Jul 29 – Aug 12 |
| Potatoes | — | — | Apr 9 – Apr 30 | — |
| Swiss Chard | — | — | Apr 16 – May 14 | Jul 29 – Aug 12 |
| Cilantro | — | — | Apr 16 – May 7 | Aug 12 – Sep 2 |
| Green Beans | — | — | May 7 – May 28 | Jul 22 – Aug 5 |
| Sweet Corn | — | — | May 7 – May 21 | — |
| Sweet Potatoes | — | May 14 – Jun 4 | — | — |
| Garlic | — | — | — | Sep 23 – Oct 28 |
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 Independence #1, IA weather station, 13 km away (elevation 1,010 ft (308 m)).
Frost dates near Winthrop
- Quasqueton Apr 30 · Oct 7
- Masonville May 3 · Oct 4
- Independence Apr 30 · Oct 7
- Lamont May 4 · Oct 1
- Aurora May 4 · Oct 1
- Rowley Apr 30 · Oct 7
- Stanley May 4 · Oct 1
- Dundee May 3 · Oct 4
- Hazleton Apr 30 · Oct 9
- Troy Mills May 3 · Oct 7
Frequently asked questions
When is the last frost in Winthrop, IA?
The median last spring frost in Winthrop, IA is April 30. There is still about a 10% chance of frost after May 12, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Winthrop, IA?
The median first fall frost is October 7, with about a 10% chance of frost before September 23.
How long is the growing season in Winthrop, IA?
About 160 days between the median last spring frost and first fall frost.
What planting zone is Winthrop, IA?
Winthrop, IA is in USDA hardiness zone 5a.