Thomson, IL frost dates
Last spring frostApr 13median date
First fall frostOct 26median date
Growing season196 daysfrost-free
Hardiness zone5bZone 5b
How Thomson compares
- In 8 years out of 10, the last spring frost in Thomson falls between April 1 and April 28, a 27-day window. The first fall frost falls between October 13 and November 7.
- The median last frost is 4 days earlier than the Illinois median of Apr 17.
- Its 196-day growing season is longer than 78% of the 1,287 Illinois places with a regular frost season (state median 187 days).
- The last frost is 18 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 132 nights a year at or below 32°F.
- Compared with Davenport, IA, 63 km away, the last frost here is 10 days earlier than there and the growing season is 21 days longer.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 1 |
| 50% (median) | April 13 |
| 10% (safe for tender plants) | April 28 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | October 13 |
| 50% (median) | October 26 |
| 90% (late) | November 7 |
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 Thomson, IL
Thomson, IL frost dates — last frost Apr 13, first frost Oct 26, zone 5b. whenisthelastfrost.com
Crop
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Start indoors: Jan 19 to Feb 2Transplant outside: Mar 16 to Mar 30
Start indoors: Feb 2 to Feb 16Transplant outside: Apr 27 to May 11
Start indoors: Feb 2 to Feb 16Transplant outside: Apr 27 to May 11
Start indoors: Feb 16 to Mar 2Transplant outside: Apr 20 to May 4
Start indoors: Feb 16 to Mar 2Transplant outside: Mar 23 to Apr 6Sow outdoors: Mar 16 to Apr 20Plant for fall: Aug 31 to Sep 28
Start indoors: Feb 16 to Mar 2Transplant outside: Mar 16 to Mar 30Sow outdoors: Mar 16 to Mar 30Plant for fall: Aug 17 to Sep 7
Start indoors: Feb 16 to Mar 2Transplant outside: Mar 30 to Apr 13Plant for fall: Jul 20 to Aug 10
Start indoors: Feb 16 to Mar 2Transplant outside: Mar 23 to Apr 6Plant for fall: Jul 20 to Aug 10
Start indoors: Feb 16 to Mar 2Transplant outside: Mar 30 to Apr 13Plant for fall: Jul 20 to Aug 10
Start indoors: Mar 2 to Mar 16Transplant outside: May 4 to May 18Sow outdoors: May 4 to May 18
Start indoors: Mar 2 to Mar 16Transplant outside: Apr 20 to May 4
Sow outdoors: Mar 2 to Mar 23Plant for fall: Aug 3 to Aug 24
Sow outdoors: Mar 2 to Mar 23Plant for fall: Aug 31 to Sep 21
Sow outdoors: Mar 9 to Apr 20Plant for fall: Sep 14 to Oct 5
Start indoors: Mar 16 to Mar 23Transplant outside: Apr 27 to May 4Sow outdoors: Apr 20 to May 4Plant for fall: Aug 10 to Aug 24
Start indoors: Mar 16 to Mar 23Sow outdoors: Apr 20 to May 4Plant for fall: Aug 17 to Aug 31
Start indoors: Mar 16 to Mar 23Sow outdoors: Apr 20 to May 4
Start indoors: Mar 16 to Mar 23Transplant outside: Apr 27 to May 11
Sow outdoors: Mar 23 to Apr 20Plant for fall: Aug 3 to Aug 17
Sow outdoors: Mar 23 to Apr 20Plant for fall: Aug 17 to Aug 31
Sow outdoors: Mar 23 to Apr 13
Sow outdoors: Mar 30 to Apr 27Plant for fall: Aug 17 to Aug 31
Sow outdoors: Mar 30 to Apr 20Plant for fall: Aug 31 to Sep 21
Sow outdoors: Apr 20 to May 11Plant for fall: Aug 10 to Aug 24
Sow outdoors: Apr 20 to May 4
Transplant outside: Apr 27 to May 18
Plant for fall: Oct 12 to Nov 16
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Thomson, IL
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Jan 19 – Feb 2 | Mar 16 – Mar 30 | — | — |
| Peppers | Feb 2 – Feb 16 | Apr 27 – May 11 | — | — |
| Eggplant | Feb 2 – Feb 16 | Apr 27 – May 11 | — | — |
| Tomatoes | Feb 16 – Mar 2 | Apr 20 – May 4 | — | — |
| Lettuce | Feb 16 – Mar 2 | Mar 23 – Apr 6 | Mar 16 – Apr 20 | Aug 31 – Sep 28 |
| Kale | Feb 16 – Mar 2 | Mar 16 – Mar 30 | Mar 16 – Mar 30 | Aug 17 – Sep 7 |
| Broccoli | Feb 16 – Mar 2 | Mar 30 – Apr 13 | — | Jul 20 – Aug 10 |
| Cabbage | Feb 16 – Mar 2 | Mar 23 – Apr 6 | — | Jul 20 – Aug 10 |
| Cauliflower | Feb 16 – Mar 2 | Mar 30 – Apr 13 | — | Jul 20 – Aug 10 |
| Okra | Mar 2 – Mar 16 | May 4 – May 18 | May 4 – May 18 | — |
| Basil | Mar 2 – Mar 16 | Apr 20 – May 4 | — | — |
| Peas | — | — | Mar 2 – Mar 23 | Aug 3 – Aug 24 |
| Spinach | — | — | Mar 2 – Mar 23 | Aug 31 – Sep 21 |
| Radishes | — | — | Mar 9 – Apr 20 | Sep 14 – Oct 5 |
| Cucumbers | Mar 16 – Mar 23 | Apr 27 – May 4 | Apr 20 – May 4 | Aug 10 – Aug 24 |
| Zucchini & Summer Squash | Mar 16 – Mar 23 | — | Apr 20 – May 4 | Aug 17 – Aug 31 |
| Winter Squash & Pumpkins | Mar 16 – Mar 23 | — | Apr 20 – May 4 | — |
| Melons & Watermelon | Mar 16 – Mar 23 | Apr 27 – May 11 | — | — |
| Carrots | — | — | Mar 23 – Apr 20 | Aug 3 – Aug 17 |
| Beets | — | — | Mar 23 – Apr 20 | Aug 17 – Aug 31 |
| Potatoes | — | — | Mar 23 – Apr 13 | — |
| Swiss Chard | — | — | Mar 30 – Apr 27 | Aug 17 – Aug 31 |
| Cilantro | — | — | Mar 30 – Apr 20 | Aug 31 – Sep 21 |
| Green Beans | — | — | Apr 20 – May 11 | Aug 10 – Aug 24 |
| Sweet Corn | — | — | Apr 20 – May 4 | — |
| Sweet Potatoes | — | Apr 27 – May 18 | — | — |
| Garlic | — | — | — | Oct 12 – Nov 16 |
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 Fulton L&D #13, IL weather station, 11 km away (elevation 591 ft (180 m)).
Frost dates near Thomson
- Savanna May 2 · Oct 7
- Fulton Apr 13 · Oct 26
- Chadwick May 2 · Oct 7
- Mount Carroll May 2 · Oct 7
- Morrison Apr 26 · Oct 13
- Lanark May 2 · Oct 7
- Milledgeville Apr 29 · Oct 7
- Albany Apr 22 · Oct 16
- Fenton Apr 26 · Oct 13
- Lyndon Apr 26 · Oct 13
Frequently asked questions
When is the last frost in Thomson, IL?
The median last spring frost in Thomson, IL is April 13. There is still about a 10% chance of frost after April 28, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Thomson, IL?
The median first fall frost is October 26, with about a 10% chance of frost before October 13.
How long is the growing season in Thomson, IL?
About 196 days between the median last spring frost and first fall frost.
What planting zone is Thomson, IL?
Thomson, IL is in USDA hardiness zone 5b.