Big news for the gardening community.
The U.S. Department of Agriculture released a new USDA Plant Hardiness Zone Map and if you didn’t already suspect, Indiana got warmer. The updated map was released November 15, 2023.
The 2023 hardiness map is the analysis of average lowest temperatures for about 30 years – 1991 to 1920. When the 2012 map came out, Indianapolis moved from Zone 5b (-15 to -10 degrees F) to 6a (-10 to -5 degrees F).
The 2023 version has Indy in Zone 6b (0 to -5 degrees F). Northern Indiana is in 6a, with a section of the western edge as 5b. Most of Indiana south of Indianapolis is 6b, with the Ohio River counties at 7a. Yikes…7a is almost tropical. That’s quite a change over 30 years.
Chris Daly, director of the PRISM Climate Group at Oregon State University, told NPR, “the 2023 map is about 2.5 degrees Fahrenheit warmer than the 2012 map across the contiguous U.S. Daly says the new map means about half the country has shifted into a new half zone and half hasn’t. In some locations, people may find they can grow new types of flowers, fruits, vegetables and plants.”
What do updated USDA Zones mean for gardeners?
Theoretically, it means if a plant is labeled hardy to 6a or 6b, it should survive our average lowest temperature. I think that’s probably all right as a guide for perennials, temperennials and maybe even some tropicals (with good mulch).
However, trees, shrubs and woody vines are a different story. Back in 2012 when the USDA changed Indy from 5b to 6a, Purdue University recommended sticking with woody plants rated at least USDA Zone 5a (-20 degrees F to -15 degrees F).
Trees and shrub are more costly than perennials. And woody plants hold a more permanent place and structure in our landscapes. That means the plants may have to survive colder than normal temps on occasion.
With woody plants, the roots may survive colder than normal temperatures, but the branches may not. The last thing you want is to replace your favorite Japanese maple that finally reached maturity because the limbs froze.
What should gardeners do differently?
Probably not much. Go ahead and plant some temperennials and see how they do. Push the envelope with USDA Zone 6b or 7a perennials, or maybe 7b in certain microclimates you may have.
Gardeners may be able to sow seeds or plant transplants of edible plants earlier outdoors. You may be able to experiment with more culturally exotic vegetables and fruits, not to mention flowers.
Most of us probably aren’t surprised by this news. But in some ways, it’s comforting to know that science recognizes what we’ve been experiencing. But it’s also a cautionary tale that tells us the climate is changing.
No surprise Indiana is warmer
As the climate warms, plants may bloom or fruit earlier than the arrival of migrating birds, insects and other wildlife. When wildlife does arrive, the nectar, seeds and fruits are long past. As you know, these kinds of conditions affect our whole environment.
So, while we may relish this “go ahead and give those plants a try” opportunity, we need to keep in mind what’s happening around us and doing our best to be responsible and protect our environment the best we can.
You can check your exact USDA Zone by plugging in your ZIP Code.