New USDA Plant Hardiness Zone Map - Illinois State Climatologist

Skip to content

The USDA has just released their new Plant Hardiness Zone Map. This is a much-needed update using the 30-year period of 1976-2005 versus the old USDA map which used the period 1974-1986. One of the outstanding features of the new map is the northward shift of the hardiness zones in Illinois. For example, the boundary between zones 5 and 6 have shifted about 60 miles to the north. Zone 4 has left Illinois in the new map. In addition, the new map shows a lot more detail including the warming effect of the Chicago urban area (see map below). In the second figure, the minimum winter temperature for each year is shown for Champaign-Urbana. The  old USDA plant hardiness zone map used an unusually short period during one of the colder periods in the record (1974-1986). The general trend in the data shows an increase in the minimum winter temperature from the late 1800s to about 1950, followed by a cooling trend to the 1980s, and finishing with a warming trend through 2005. Interestingly, the last few years showed a cooling trend – except for this year when our coldest temperature so far is 4°F. The other important feature in the second figure is that even if an area changes Zones, there is still a lot of year to year variability in the minimum temperature for winter. For example, while Champaign-Urbana is nearly classified as Zone 6 in the new map, Champaign-Urbana dipped into Zone 4 a few times (-20°F or less) in the last 30 years.  In fact, as a gardener I would say that the period from the 1930s to the early 1970s was more benign and less challenging than the 1980s and 1990s with respect to winter temperatures. Summer conditions would be another story since the 1930s and 1950s were marred by severe droughts.

6 Replies to “New USDA Plant Hardiness Zone Map”

1. You have provided some interesting insight on this and your perspective as a gardener is also welcome. I am curious if you have any methodology for forecasting future drought? Do you expect that at some point Illinois will return to the drought conditions of the past? I ask because I have have looked at ESRL water vapor data at 1000mb (near surface for casual readers) and there has been an increase into the 21st Century. Can the extra water vapor lower drought risk? Thanks for any insight.

2. Will you address Sundance’s question? I am curious since it has been an extremely hot and dry summer for much of the country.

3. If only we could forecast drought conditions. It always seems obvious in hindsight but I’ve seen several cases over the years where I thought we were in trouble. And then the rains came just in time, but just not this year.

4. It’s too hot in Chicago

5. It’s too cold in Northeastern IL zone 5b.

6. Al Gore wants to know when the Illinois River will boil.

Leave a Reply

Your email address will not be published. Required fields are marked *

Comment *

Name

Email

Website

Δ

Post navigation

Previous PostPrevious Severe Weather in JanuaryNext PostNext Cold In Alaska Search for: Search

  

Subscribe to the Water Survey’s newsletter

Recent Posts

• 2026 Began with a Cold and Dry January
• 2025 Was Warm and Dry in Illinois
• Cool and Dry Start to Winter
• Fall Ended and Winter Really Began in November
• A Warm and Dry October Ushers in Real Fall

Recent Comments

• Brian on Where Is the Snow in Illinois?
• tencars on 90th Anniversary of the Tri-State Tornado: Illinois’ Worst Tornado Disaster
• Anonymous on November in Illinois – Cool and Dry with a Dash of Snow
• Nicki Jenns on Rainfall and Temperatures Across the Midwest in August
• Michael Zvetina on 25th Anniversary of the Great Flood of 1993

Categories

• Agriculture
• Chicago
• Climate Change
• Climate Monitoring
• Cold
• Drought
• El Nino
• Fall
• Flooding
• Frost
• Hazards
• Heat
• Heavy Rains
• Observations
• Seasonal Outlooks
• Severe Weather
• Snow
• Spring
• Tornado
• Updates
• Weather
• Winter

Archives

Archives Select Month February 2026 January 2026 December 2025 November 2025 October 2025 September 2025 August 2025 July 2025 June 2025 May 2025 April 2025 March 2025 February 2025 January 2025 December 2024 November 2024 October 2024 September 2024 August 2024 July 2024 June 2024 May 2024 April 2024 March 2024 February 2024 January 2024 December 2023 November 2023 October 2023 September 2023 August 2023 July 2023 June 2023 May 2023 April 2023 March 2023 February 2023 January 2023 December 2022 November 2022 October 2022 September 2022 August 2022 July 2022 June 2022 May 2022 April 2022 March 2022 February 2022 January 2022 December 2021 November 2021 October 2021 September 2021 August 2021 July 2021 June 2021 May 2021 April 2021 March 2021 February 2021 January 2021 December 2020 November 2020 October 2020 September 2020 August 2020 July 2020 June 2020 May 2020 April 2020 March 2020 February 2020 January 2020 December 2019 November 2019 October 2019 September 2019 August 2019 July 2019 June 2019 May 2019 April 2019 March 2019 February 2019 January 2019 December 2018 November 2018 October 2018 September 2018 August 2018 July 2018 June 2018 May 2018 April 2018 March 2018 February 2018 January 2018 December 2017 November 2017 October 2017 September 2017 August 2017 July 2017 June 2017 May 2017 April 2017 March 2017 February 2017 January 2017 December 2016 November 2016 October 2016 September 2016 August 2016 July 2016 June 2016 May 2016 April 2016 March 2016 February 2016 January 2016 December 2015 November 2015 October 2015 September 2015 August 2015 July 2015 June 2015 May 2015 April 2015 March 2015 February 2015 January 2015 December 2014 November 2014 October 2014 September 2014 August 2014 July 2014 June 2014 May 2014 April 2014 March 2014 February 2014 July 2013 June 2013 May 2013 April 2013 March 2013 February 2013 January 2013 December 2012 November 2012 October 2012 September 2012 August 2012 July 2012 June 2012 May 2012 April 2012 March 2012 February 2012 January 2012 December 2011 November 2011 October 2011 September 2011 August 2011 July 2011 June 2011 May 2011 April 2011 March 2011 February 2011 January 2011 December 2010 November 2010 October 2010 September 2010 August 2010 July 2010 June 2010 May 2010 April 2010 March 2010