Figs In Boston: New Plant Hardiness Zones Reflect Dramatic Global Warming

The Department of Agriculture’s plant hardiness maps are finally reflecting a fact that gardeners have already realized — the United States is changing dramatically with global warming pollution. The USDA released a new plant hardiness zone map to replace the 1990 map, reflecting twenty years of rapid global warming:

The 1990 map was based on temperatures from 1974 to 1986, the new map from 1976 to 2005. The nation’s average temperature from 1976 to 2005 was two-thirds of a degree higher than it was during the old time period, according to the National Climatic Data Center.

The new map is generally one half-zone warmer than the previous map throughout much of the United States. Cities as varied as Boston, Honolulu, St. Louis, Des Moines, Iowa, St. Paul, Minnesota, and Fairbanks, Alaska, are in newer, warmer zones. Almost all of Ohio, Nebraska and Texas are in warmer zones.

The Washington Post quoted several experts who noted the new map, whose changes in hardiness zones are based on rising minimum temperatures across the nation, isn’t news to gardeners.

Boston University biology professor Richard Primack:

People who grow plants are well aware of the fact that temperatures have gotten more mild throughout the year, particularly in the wintertime.

George Ball, chairman and CEO of the seed company W. Atlee Burpee:

Climate change, which has been in the air for a long time, is not big news to gardeners.

Stanford University biology professor Terry Root:

It is great that the federal government is catching up with what the plants themselves have known for years now: The globe is warming and it is greatly influencing plants (and animals).

Vaughn Speer, an 87-year-old master gardener in Ames, Iowa, said he has seen redbud trees, appear ten miles north of their traditional limit in recent years. Our nation’s forests are dying with the changes. Lodgepole pines, aspens, walnut trees, and other dominant species adapted to a climate without greenhouse pollution are already suffering in our hotter planet.


In coming decades, the rate of global warming will increase significantly, a result of the rapid rise in fossil fuel pollution, making it ever more difficult for plants to adapt, and destabilizing all of our nation’s ecosystems.