Warmer Temperatures Make New USDA Plant Zone Map Obsolete

New Approach to Mapping Plant Hardiness Zones Accounts for Effects of Climate Change

City College of New York news release

A map of warming across the nation showing how much USDA plant hardiness zones will warm, in degrees Farhenheit. (Credit: Nir Krakauer)
Gardeners and landscapers may want to rethink their fall tree plantings. Warming temperatures have already made the U.S. Department of Agriculture’s new cold-weather planting guidelines obsolete, according to Dr. Nir Krakauer, assistant professor of civil engineering in The City College of New York’s Grove School of Engineering.Professor Krakauer developed a new method to map cold-weather zones in the United States that takes rapidly rising temperatures into account. Analyzing recent weather data, he overhauled the Department of Agriculture’s latest plant zone map released in January. 

The new USDA Plant Hardiness Zone Map, which predicts which trees and perennials can survive the winter in a given region, was a long time coming. Temperature boundaries shown in the latest version have shifted northward since the last one appeared in 1990. But the true zones have moved even further, according to Professor Krakauer’s calculations.

Over one-third of the country has already shifted half-zones compared to the current release, and over one-fifth has shifted full zones,” Professor Krakauer wrote this summer in the journal “Advances in Meteorology.”

This means that fig trees, once challenged by frosty temperatures above North Carolina, are already weathering New York City winters thanks to changing temperatures and the insulating effect of the metropolis. Camellias, once happiest south of Ohio, may now be able to shrug off Detroit winters.

The USDA divides the country into zones based on their annual minimum temperatures – frigid dips that determine which plants perish overnight or live to flower another day. (Each zone has a minimum temperature range of 10 degrees Fahrenheit; half zones have a 5-degree range.)

Professor Krakauer found a weakness in how the agency came up with the zones, however. The USDA averaged annual minimum temperatures over a 30-year span, from 1976 to 2005, but winters have warmed significantly over that period. Zones now average about 2 degrees Fahrenheit warmer than the USDA’s 30-year average.

“What is happening is that the winter is warming faster than the summer. Since [my] hardiness temperatures are based on minimum temperatures each year, they are changing faster than the average temperatures,” Professor Krakauer said. He found that these lowest yearly temperatures warmed roughly two and a half times faster than the average temperatures.

His analysis also showed that the country is changing unevenly; more warming is occurring over the eastern interior and less in the Southwest.

Professor Krakauer’s technique will allow gardeners and farmers to reassess more frequently what will survive the next year’s winter. “The idea is that you could use this method to keep updating the zone map year by year instead of waiting for the official map – just keep adding new data and recalculate.”

He noted that similar analyses could distinguish long-lasting climate trends – in wind or rainfall, for example – from year-to-year weather variations to distinguish between what some are calling the recent “weird weather” and the natural variations in global weather.

Reference: Nir Y. Krakauer. Estimating Climate Trends: Application to United States Plant Hardiness Zones. Advances in Meteorology, Vol. 2012 (2012), Article ID 404876, doi:10.1155/2012/404876

15 Responses to Warmer Temperatures Make New USDA Plant Zone Map Obsolete

  1. Dano says:

    To be clear, this paper is in an open source journal and I’m not sure how many of his peers read it to weigh in.

    There are many places in this country that have ‘zone creep’ and many gardeners are pushing zones. Yet, we still have winters that go according to type and kill your plants that you pushed or didn’t have a microclimate for.

    That is: the maps aren’t obsolete. They are still a good guide. You still need plant knowledge to go with them and very few experienced gardeners just go by the map. You need the heat zone map as well, and for the west, Sunset is still better.



  2. jyyh says:

    Peaches – from Finland
    Granted, the tree was on the warmest corner of the about 3rd warmest of Finnish towns but on the eighties people might have laughed at the idea. No doubt there are similar experiences around the NH.

  3. Peter M says:


    the Map which is revised to 2006 is obsolete. I am growing stuff like windmill palms in my garden in Connecticut (in the ground- not in containers)- that are flourishing. Something is changing rapidly- or my skills as a Gardner are reaching God like proportions.

    These fan palms from Asia

  4. TJinBoulderUT says:

    A problem we have here in Southern UT, at 6500 feet in elevation, is the warm winter temps bringing fruit trees to bloom too early with a late frost killing buds and messing the fruit production. Also, bees come out of their hives before any flowering plants are available for support. Zones may be creeping, but the plants,insects and birds are not necessarily adjusting as quickly. This may become a real challenge.

  5. Joan Savage says:

    A shift in minimum temperatures is a convenient way to show one of the aspects of climate change that affects planting and harvest.

    However, it really doesn’t address three crucial plant growth factors that are evident in climate change: increased maximum temperatures, greater variability in rainfall, and more energy-intense weather.

  6. Rabid Doomsayer says:

    It is difficult. One or two winters does not make a new climate regime. However in an environment of accelerating change, thirty year averaging leaves us lagging in catching up with those changes.

  7. Matthew Kahn says:


    You are persuasive! I’m glad to see a high quality post about climate change adaptation. Professor Krakauer has created a valuable map and people will respond to this new news. This is a nice example of learning and probability updating. Armed with this new information, planters will change their investment behavior. This is the microeconomics of adaptation at work.

    best, Matt Kahn

  8. Joe Romm says:

    I’m a big fan of dealing with the painful reality of climate change, since that is what the powerful few who block action are forcing on countless future generations. My preferred terms are “triage, abandonment, and misery” since that I fear will constitute the bulk of what most people think of as “adaptation” if we keep on our path of 10F warming. As John Holdren, now science advisor, put it “We basically have three choices: mitigation, adaptation and suffering. We’re going to do some of each. The question is what the mix is going to be. The more mitigation we do, the less adaptation will be required and the less suffering there will be.”

  9. Paul Magnus says:

    Its more than the map which is/will obsolete…

  10. Mulga Mumblebrain says:

    It’ll be mangoes soon.

  11. Mulga Mumblebrain says:

    It’s the rapidity of change, isn’t it. It’s hard to get the Dunning-Krugerites to acknowledge that, or the knowing liars to admit it.

  12. Mulga Mumblebrain says:

    One hot, dry day, with a blast furnace wind, coming after weeks without rain, will kill any tender thing, stone dead. I lost half the plants that I had established here during the drought years from 2001 (when we arrived) and 2008. No amount of watering, which just runs away into the dessicated soil, or mulching makes any difference. The trees that survived are the drought hardy ones, and their shade is beginning to produce more benign micro-climates, but I dread the next drought, let alone fires.

  13. John McCormick says:

    Joe, I agree with you and Dr. Holdren while I keep reminding myself: in the long run we cannot adapt to a moving target. Agriculture will eventually collapse.

  14. Dennis Tomlinson says:

    Right you are mulga. PETM was not accompanied by a mass extinction – only regional extinctions due to anoxia from the oxidation of localized methane releases. The climactic changes occurred on timescales measured in millenia. The earth warmed a total of 6C at an average rate of 0.3C/k-yr. There was time for adaptation by both fauna and flora. Crocodiles and palm trees flourished in Alaska. This time it will be different.

  15. Mulga Mumblebrain says:

    I heard some farming Dunning-Krugerites on the radio this morning. They are launching a High Court challenge to the Gummint’s water conservation laws regarding the Murray-Darling, our major river system. Not against the risible amounts to be returned to the system to save wet-lands, riverine forest and biodiversity. No, no-they want NO water returned and EVERY drop available gifted to them. One droog mumbled some enlightening rubbish about putting ‘people’ before ‘frogs and gum-trees’, apparently being one of those mental midgets (we have them in battalions here, particularly amongst the worst of the rural numbskulls)who imagine that humanity can keep on raping the environment and destroying every other species, yet still survive themselves.