WASHINGTON — The government's colorful map of planting zones is being updated for a warmer 21st century.
The official guide for 80 million gardeners and a staple on seed packets reflects a new reality: The coldest day of the year isn't as cold as it used to be. So some plants that once seemed too vulnerable to cold can now survive farther north.
It's the first time since 1990 that the U.S. Department of Agriculture has updated the map and much has changed. Nearly entire states, such as Ohio, Nebraska and Texas, are in warmer zones.
The new guide, unveiled Wednesday at the National Arboretum, also uses better weather data and offers more interactive technology.
"It truly does reflect state of the art," said USDA chief scientist Catherine Woteki.
Gardeners can register their zip code into the online map and their zone will pop up. It shows the exact average coldest temperature for each of the 26 zones, even though zones are based on five degree increments.
For example, Des Moines, Iowa, used to be in zone 5a, meaning the lowest temperature on average was between minus 15 and minus 20 degrees Fahrenheit. Now it's 5b, which has a coldest temperature of 10 to 15 degrees below zero.
"People who grow plants are well aware of the fact that temperatures have gotten more mild throughout the year, particularly in the winter time," said Boston University biology professor Richard Primack. "There's a lot of things you can grow now that you couldn't grow before."
He uses the giant fig tree in his suburban Boston yard as an example.
"People don't think of figs as a crop you can grow in the Boston area. You can do it now," he said.
An earlier effort to update the planting map caused a bit of an uproar when the USDA in 2003 decided not to use a map it commissioned that reflected warmer weather. The Arbor Day Foundation later issued its own hardiness guide that had the toastier climate zones. The new federal map is very similar to the one the private plant group adopted six years ago, said Arbor Day Foundation Vice President Woodrow Nelson.
In Des Moines, Jerry Holub, a manager for the Earl May Nursery chain, doesn't think the warmer zone will have much of an impact on gardeners. But he said this may mean residents can even try passion flowers.
"Now you can put them in safely, when you couldn't before," he said.
AP Writer Michael J. Crumb contributed to this report from Des Moines.
Plant map: http://planthardiness.ars.usda.gov/PHZMWeb/