Union, IL frost dates
Last spring frostApr 28median date
First fall frostOct 12median date
Growing season167 daysfrost-free
Hardiness zone5bZone 5b
How Union compares
- In 8 years out of 10, the last spring frost in Union falls between April 15 and May 14, a 29-day window. The first fall frost falls between September 28 and October 27.
- The median last frost is 11 days later than the Illinois median of Apr 17.
- Its 167-day growing season is longer than 4% of the 1,287 Illinois places with a regular frost season (state median 187 days).
- The last frost is typical for zone 5b, where the median is May 1.
- The weather station records an average of 147 nights a year at or below 32°F.
- Compared with Elgin, IL, 26 km away, the last frost here is 2 days later than there and the growing season is 8 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 15 |
| 50% (median) | April 28 |
| 10% (safe for tender plants) | May 14 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 28 |
| 50% (median) | October 12 |
| 90% (late) | October 27 |
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 Union, IL
Union, IL frost dates — last frost Apr 28, first frost Oct 12, zone 5b. whenisthelastfrost.com
Crop
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Start indoors: Feb 3 to Feb 17Transplant outside: Mar 31 to Apr 14
Start indoors: Feb 17 to Mar 3Transplant outside: May 12 to May 26
Start indoors: Feb 17 to Mar 3Transplant outside: May 12 to May 26
Start indoors: Mar 3 to Mar 17Transplant outside: May 5 to May 19
Start indoors: Mar 3 to Mar 17Transplant outside: Apr 7 to Apr 21Sow outdoors: Mar 31 to May 5Plant for fall: Aug 17 to Sep 14
Start indoors: Mar 3 to Mar 17Transplant outside: Mar 31 to Apr 14Sow outdoors: Mar 31 to Apr 14Plant for fall: Aug 3 to Aug 24
Start indoors: Mar 3 to Mar 17Transplant outside: Apr 14 to Apr 28Plant for fall: Jul 6 to Jul 27
Start indoors: Mar 3 to Mar 17Transplant outside: Apr 7 to Apr 21Plant for fall: Jul 6 to Jul 27
Start indoors: Mar 3 to Mar 17Transplant outside: Apr 14 to Apr 28Plant for fall: Jul 6 to Jul 27
Start indoors: Mar 17 to Mar 31Transplant outside: May 19 to Jun 2Sow outdoors: May 19 to Jun 2
Start indoors: Mar 17 to Mar 31Transplant outside: May 5 to May 19
Sow outdoors: Mar 17 to Apr 7Plant for fall: Jul 20 to Aug 10
Sow outdoors: Mar 17 to Apr 7Plant for fall: Aug 17 to Sep 7
Sow outdoors: Mar 24 to May 5Plant for fall: Aug 31 to Sep 21
Start indoors: Mar 31 to Apr 7Transplant outside: May 12 to May 19Sow outdoors: May 5 to May 19Plant for fall: Jul 27 to Aug 10
Start indoors: Mar 31 to Apr 7Sow outdoors: May 5 to May 19Plant for fall: Aug 3 to Aug 17
Start indoors: Mar 31 to Apr 7Sow outdoors: May 5 to May 19
Start indoors: Mar 31 to Apr 7Transplant outside: May 12 to May 26
Sow outdoors: Apr 7 to May 5Plant for fall: Jul 20 to Aug 3
Sow outdoors: Apr 7 to May 5Plant for fall: Aug 3 to Aug 17
Sow outdoors: Apr 7 to Apr 28
Sow outdoors: Apr 14 to May 12Plant for fall: Aug 3 to Aug 17
Sow outdoors: Apr 14 to May 5Plant for fall: Aug 17 to Sep 7
Sow outdoors: May 5 to May 26Plant for fall: Jul 27 to Aug 10
Sow outdoors: May 5 to May 19
Transplant outside: May 12 to Jun 2
Plant for fall: Sep 28 to Nov 2
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Union, IL
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Feb 3 – Feb 17 | Mar 31 – Apr 14 | — | — |
| Peppers | Feb 17 – Mar 3 | May 12 – May 26 | — | — |
| Eggplant | Feb 17 – Mar 3 | May 12 – May 26 | — | — |
| Tomatoes | Mar 3 – Mar 17 | May 5 – May 19 | — | — |
| Lettuce | Mar 3 – Mar 17 | Apr 7 – Apr 21 | Mar 31 – May 5 | Aug 17 – Sep 14 |
| Kale | Mar 3 – Mar 17 | Mar 31 – Apr 14 | Mar 31 – Apr 14 | Aug 3 – Aug 24 |
| Broccoli | Mar 3 – Mar 17 | Apr 14 – Apr 28 | — | Jul 6 – Jul 27 |
| Cabbage | Mar 3 – Mar 17 | Apr 7 – Apr 21 | — | Jul 6 – Jul 27 |
| Cauliflower | Mar 3 – Mar 17 | Apr 14 – Apr 28 | — | Jul 6 – Jul 27 |
| Okra | Mar 17 – Mar 31 | May 19 – Jun 2 | May 19 – Jun 2 | — |
| Basil | Mar 17 – Mar 31 | May 5 – May 19 | — | — |
| Peas | — | — | Mar 17 – Apr 7 | Jul 20 – Aug 10 |
| Spinach | — | — | Mar 17 – Apr 7 | Aug 17 – Sep 7 |
| Radishes | — | — | Mar 24 – May 5 | Aug 31 – Sep 21 |
| Cucumbers | Mar 31 – Apr 7 | May 12 – May 19 | May 5 – May 19 | Jul 27 – Aug 10 |
| Zucchini & Summer Squash | Mar 31 – Apr 7 | — | May 5 – May 19 | Aug 3 – Aug 17 |
| Winter Squash & Pumpkins | Mar 31 – Apr 7 | — | May 5 – May 19 | — |
| Melons & Watermelon | Mar 31 – Apr 7 | May 12 – May 26 | — | — |
| Carrots | — | — | Apr 7 – May 5 | Jul 20 – Aug 3 |
| Beets | — | — | Apr 7 – May 5 | Aug 3 – Aug 17 |
| Potatoes | — | — | Apr 7 – Apr 28 | — |
| Swiss Chard | — | — | Apr 14 – May 12 | Aug 3 – Aug 17 |
| Cilantro | — | — | Apr 14 – May 5 | Aug 17 – Sep 7 |
| Green Beans | — | — | May 5 – May 26 | Jul 27 – Aug 10 |
| Sweet Corn | — | — | May 5 – May 19 | — |
| Sweet Potatoes | — | May 12 – Jun 2 | — | — |
| Garlic | — | — | — | Sep 28 – Nov 2 |
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 Marengo, IL weather station, 9 km away (elevation 814 ft (248 m)).
Frost dates near Union
- Marengo Apr 28 · Oct 12
- Huntley Apr 25 · Oct 22
- Woodstock Apr 25 · Oct 22
- Alden Apr 25 · Oct 22
- Hampshire Apr 26 · Oct 18
- Crystal Lake Apr 25 · Oct 22
- Lake In The Hills Apr 25 · Oct 22
- Gilberts Apr 26 · Oct 18
- Burlington Apr 26 · Oct 18
- Genoa Apr 24 · Oct 18
Frequently asked questions
When is the last frost in Union, IL?
The median last spring frost in Union, IL is April 28. There is still about a 10% chance of frost after May 14, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Union, IL?
The median first fall frost is October 12, with about a 10% chance of frost before September 28.
How long is the growing season in Union, IL?
About 167 days between the median last spring frost and first fall frost.
What planting zone is Union, IL?
Union, IL is in USDA hardiness zone 5b.