These dates are for Wheaton, IL.
Get your own frost data at the Illinois Climatologist Office
Last Frost
Earliest: April 9th
90%: April 20th
50%: May 6th
Latest: June 12th
I personally use April 15th as my date for joy but I live dangerously! May 1 is the traditional first day of planting in this area.
First Frost
Earliest: September 22th
90%: September 24th
50%: October 10th
20%: October 20th
Latest: November 1st
I personally use October 15th as my date for concern
Observed History
| Last Frost | First Frost | |
| 2007 | October 28 | |
| 2008 | Apr 28 | October 28 |
| 2009 | May 17 (barely) | October 11 |
| 2010 | May 11 | October 19 |
| 2011 | May 5 (barely) | October 2 (barely) |
Terms and Definitions
Frost
A term to describe temperatures that drop below 36° F for a short period, typically damaging unprotected vegetation. Frost protection devices such as blankets, cold frames, buckets and other coverings are sufficient to protect most plants by not allowing water to freeze on the plant but on the protection device instead.
Hard Freeze
A term to describe temperatures that drop below 32° F and remain there for several hours, typically killing all vegetation. No amount of protection, other than supplemental heat, will help.