WASHINGTON (AP) — Global warming is hitting not just home, but garden. The
color-coded map of planting zones often seen on the back of seed packets is
being updated by the government, illustrating a hotter 21st century.
It’s the first time since 1990 that the U.S. Department of Agriculture has
revised the official guide for the nation’s 80 million gardeners, and much
has changed. Nearly entire states, such as Ohio, Nebraska and Texas, are in
The new guide, unveiled Wednesday at the National Arboretum, arrives just as
many home gardeners are receiving their seed catalogs and dreaming of lush
flower beds in the spring.
It reflects a new reality: The coldest day of the year isn’t as cold as it
used to be, so some plants and trees can now survive farther north.
“People who grow plants are well aware of the fact that temperatures have
gotten more mild throughout the year, particularly in the wintertime,” said
Boston University biology professor Richard Primack. “There’s a lot of
things you can grow now that you couldn’t grow before.”
He stand the giant fig tree in his suburban Boston yard stands as an
example: “People don’t think of figs as a crop you can grow in the Boston
area. You can do it now.”
The new guide also uses better weather data and offers more interactive
technology. For example, gardeners using the online version can enter their
ZIP code and get the exact average coldest temperature.
Also, for the first time, calculations include more detailed factors such as
prevailing winds, the presence of nearby bodies of water, the slope of the
land, and the way cities are hotter than suburbs and rural areas.
The map carves up the U.S. into 26 zones based on five-degree temperature
increments. The old 1990 map mentions 34 U.S. cities in its key. On the 2012
map, 18 of those, including Honolulu, St. Louis, Des Moines, Iowa, St. Paul,
Minn., and even Fairbanks, Alaska, are in newer, warmer zones.
Those differences matter in deciding what to plant.
For example, Des Moines used to be in zone 5a, meaning the lowest
temperature on average was between minus 15 and minus 20 degrees. Now it’s
5b, which has a lowest temperature of 10 to 15 degrees below zero. Jerry
Holub, manager of a Des Moines plant nursery, said folks there might now be
able to safely grow passion flowers.
Griffin, Ga., used to be in zone 7b, where the coldest day would average
between 5 and 10 degrees. But the city is now in zone 8a, averaging a
coldest day of 10 to 15 degrees. So growing bay laurel becomes possible. It
wasn’t recommended on the old map.
“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),” Stanford University biology professor
Terry Root wrote in an email.
The changes come too late to make this year’s seed packets, but they will be
in next year’s, said George Ball, chairman and CEO of the seed company W.
Atlee Burpee, which puts the maps on packages of perennials, not annuals.
But Ball said many of his customers already know what can grow in their own
climate and how it has warmed.
“Climate change, which has been in the air for a long time, is not big news
to gardeners,” he said.
Mark Kaplan, a New York meteorologist who helped create the 1990 map, said
the latest version clearly shows warmer zones migrating north. Other experts
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.
USDA spokeswoman Kim Kaplan, who was part of the map team, repeatedly tried
to distance the new zones on the map from global warming. She said that
while much of the country is in warmer zones, the map “is simply not a good
instrument” to demonstrate climate change because it is based on just the
coldest days of the year.
David W. Wolfe, a professor of plant and soil ecology at Cornell University,
said that the USDA is being too cautious and that the map plainly reflects
The revised map “gives us a clear picture of the ‘new normal’ and will be an
essential tool for gardeners, farmers and natural resource managers as they
begin to cope with rapid climate change,” Wolfe said in an email.
The Arbor Day Foundation issued its own hardiness guide six years ago, and
the new government map is very similar, said Woodrow Nelson, a vice
president at the plant-loving organization.
“We got a lot of comments that the 1990 map wasn’t accurate anymore,” Nelson
said. “I look forward to (the new map). It’s been a long time coming.”
Nelson lives in Lincoln, Neb., where the zone warmed to a 5b. Nelson said he
used to be in a “solid 4,” but now he has Japanese maples and Fraser firs in
his yard — trees that shouldn’t survive in a zone 4.
Vaughn Speer, an 87-year-old master gardener in Ames, Iowa, said he has seen
redbud trees, one of the earliest blooming trees, a little farther north in
“They always said redbuds don’t go beyond U.S. Highway 30,” he said, “but
I’m seeing them near Roland,” 10 miles to the north.