Monmouth, IL frost dates
Last spring frostApr 22median date
First fall frostOct 15median date
Growing season176 daysfrost-free
Hardiness zone5bZone 5b
How Monmouth compares
- In 8 years out of 10, the last spring frost in Monmouth falls between April 9 and May 10, a 31-day window. The first fall frost falls between September 29 and October 27.
- The median last frost is 5 days later than the Illinois median of Apr 17.
- Its 176-day growing season is longer than 19% of the 1,287 Illinois places with a regular frost season (state median 187 days).
- The last frost is 9 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 127 nights a year at or below 32°F.
- Compared with Davenport, IA, 73 km away, the last frost here is 1 day earlier than there and the growing season is 1 day longer.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | April 9 |
| 50% (median) | April 22 |
| 10% (safe for tender plants) | May 10 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 29 |
| 50% (median) | October 15 |
| 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 Monmouth, IL
Monmouth, IL frost dates — last frost Apr 22, first frost Oct 15, zone 5b. whenisthelastfrost.com
Crop
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Start indoors: Jan 28 to Feb 11Transplant outside: Mar 25 to Apr 8
Start indoors: Feb 11 to Feb 25Transplant outside: May 6 to May 20
Start indoors: Feb 11 to Feb 25Transplant outside: May 6 to May 20
Start indoors: Feb 25 to Mar 11Transplant outside: Apr 29 to May 13
Start indoors: Feb 25 to Mar 11Transplant outside: Apr 1 to Apr 15Sow outdoors: Mar 25 to Apr 29Plant for fall: Aug 20 to Sep 17
Start indoors: Feb 25 to Mar 11Transplant outside: Mar 25 to Apr 8Sow outdoors: Mar 25 to Apr 8Plant for fall: Aug 6 to Aug 27
Start indoors: Feb 25 to Mar 11Transplant outside: Apr 8 to Apr 22Plant for fall: Jul 9 to Jul 30
Start indoors: Feb 25 to Mar 11Transplant outside: Apr 1 to Apr 15Plant for fall: Jul 9 to Jul 30
Start indoors: Feb 25 to Mar 11Transplant outside: Apr 8 to Apr 22Plant for fall: Jul 9 to Jul 30
Start indoors: Mar 11 to Mar 25Transplant outside: May 13 to May 27Sow outdoors: May 13 to May 27
Start indoors: Mar 11 to Mar 25Transplant outside: Apr 29 to May 13
Sow outdoors: Mar 11 to Apr 1Plant for fall: Jul 23 to Aug 13
Sow outdoors: Mar 11 to Apr 1Plant for fall: Aug 20 to Sep 10
Sow outdoors: Mar 18 to Apr 29Plant for fall: Sep 3 to Sep 24
Start indoors: Mar 25 to Apr 1Transplant outside: May 6 to May 13Sow outdoors: Apr 29 to May 13Plant for fall: Jul 30 to Aug 13
Start indoors: Mar 25 to Apr 1Sow outdoors: Apr 29 to May 13Plant for fall: Aug 6 to Aug 20
Start indoors: Mar 25 to Apr 1Sow outdoors: Apr 29 to May 13
Start indoors: Mar 25 to Apr 1Transplant outside: May 6 to May 20
Sow outdoors: Apr 1 to Apr 29Plant for fall: Jul 23 to Aug 6
Sow outdoors: Apr 1 to Apr 29Plant for fall: Aug 6 to Aug 20
Sow outdoors: Apr 1 to Apr 22
Sow outdoors: Apr 8 to May 6Plant for fall: Aug 6 to Aug 20
Sow outdoors: Apr 8 to Apr 29Plant for fall: Aug 20 to Sep 10
Sow outdoors: Apr 29 to May 20Plant for fall: Jul 30 to Aug 13
Sow outdoors: Apr 29 to May 13
Transplant outside: May 6 to May 27
Plant for fall: Oct 1 to Nov 5
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Monmouth, IL
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Jan 28 – Feb 11 | Mar 25 – Apr 8 | — | — |
| Peppers | Feb 11 – Feb 25 | May 6 – May 20 | — | — |
| Eggplant | Feb 11 – Feb 25 | May 6 – May 20 | — | — |
| Tomatoes | Feb 25 – Mar 11 | Apr 29 – May 13 | — | — |
| Lettuce | Feb 25 – Mar 11 | Apr 1 – Apr 15 | Mar 25 – Apr 29 | Aug 20 – Sep 17 |
| Kale | Feb 25 – Mar 11 | Mar 25 – Apr 8 | Mar 25 – Apr 8 | Aug 6 – Aug 27 |
| Broccoli | Feb 25 – Mar 11 | Apr 8 – Apr 22 | — | Jul 9 – Jul 30 |
| Cabbage | Feb 25 – Mar 11 | Apr 1 – Apr 15 | — | Jul 9 – Jul 30 |
| Cauliflower | Feb 25 – Mar 11 | Apr 8 – Apr 22 | — | Jul 9 – Jul 30 |
| Okra | Mar 11 – Mar 25 | May 13 – May 27 | May 13 – May 27 | — |
| Basil | Mar 11 – Mar 25 | Apr 29 – May 13 | — | — |
| Peas | — | — | Mar 11 – Apr 1 | Jul 23 – Aug 13 |
| Spinach | — | — | Mar 11 – Apr 1 | Aug 20 – Sep 10 |
| Radishes | — | — | Mar 18 – Apr 29 | Sep 3 – Sep 24 |
| Cucumbers | Mar 25 – Apr 1 | May 6 – May 13 | Apr 29 – May 13 | Jul 30 – Aug 13 |
| Zucchini & Summer Squash | Mar 25 – Apr 1 | — | Apr 29 – May 13 | Aug 6 – Aug 20 |
| Winter Squash & Pumpkins | Mar 25 – Apr 1 | — | Apr 29 – May 13 | — |
| Melons & Watermelon | Mar 25 – Apr 1 | May 6 – May 20 | — | — |
| Carrots | — | — | Apr 1 – Apr 29 | Jul 23 – Aug 6 |
| Beets | — | — | Apr 1 – Apr 29 | Aug 6 – Aug 20 |
| Potatoes | — | — | Apr 1 – Apr 22 | — |
| Swiss Chard | — | — | Apr 8 – May 6 | Aug 6 – Aug 20 |
| Cilantro | — | — | Apr 8 – Apr 29 | Aug 20 – Sep 10 |
| Green Beans | — | — | Apr 29 – May 20 | Jul 30 – Aug 13 |
| Sweet Corn | — | — | Apr 29 – May 13 | — |
| Sweet Potatoes | — | May 6 – May 27 | — | — |
| Garlic | — | — | — | Oct 1 – Nov 5 |
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 Monmouth, IL weather station, 4 km away (elevation 722 ft (220 m)).
Frost dates near Monmouth
- Kirkwood Apr 22 · Oct 14
- Gerlaw Apr 22 · Oct 15
- Cameron Apr 20 · Oct 19
- Little York Apr 22 · Oct 14
- Alexis Apr 22 · Oct 15
- Berwick Apr 22 · Oct 19
- Biggsville Apr 8 · Oct 29
- Smithshire Apr 22 · Oct 14
- Roseville Apr 22 · Oct 19
- Galesburg Apr 20 · Oct 19
Frequently asked questions
When is the last frost in Monmouth, IL?
The median last spring frost in Monmouth, IL is April 22. There is still about a 10% chance of frost after May 10, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Monmouth, IL?
The median first fall frost is October 15, with about a 10% chance of frost before September 29.
How long is the growing season in Monmouth, IL?
About 176 days between the median last spring frost and first fall frost.
What planting zone is Monmouth, IL?
Monmouth, IL is in USDA hardiness zone 5b.