Plant Hardiness Map
11:37 am
Mon February 27, 2012

Warming Trend in Illinois

The US Department of Agriculture is confirming what gardeners in Illinois already knew: it has become warmer in the state during recent years.  

The change can be seen in the USDA's plant hardiness map that appears on the back of packages for seeds and plants. 

State climatologist Jim Angel said the previous map was based on a much colder period in Illinois history.

“Since then we've had some milder winters in the 1990s and the early 2000s, and that's reflected in the new map,” Angel said.

Angel thinks the change will open up an opportunity for more southern climate plants to survive in Illinois.

This winter has been quite mild, especially in central and southern Illinois, but Angel said the hardiness map reflects a longer time period.

“This is based on a 30-year average so it's a very long time frame to look at these kinds of numbers,” Angel said.

“The nice thing about taking a 30-year average is it evens out those one or two years that are way off the mark. It kind of gives you an overall picture of how things might shake out.”

He said the frost-free date has been moved up roughly one week in the Spring. It has not changed for Autumn.

Angel also said that while the average temperatures in Illinois are a bit warmer, very cold winters are still possible in the state. He said that's something gardeners should take into consideration when purchasing plants.

Thanks to Illinois Public Radio